GROWTH OF INTERIOR SPRUCE AND ATTACK BY THE WHITE PINE WEEVIL,
PISSODESSTROBI (PECK) IN THE SUB BOREAL SPRUCE ZONE OF BRITISH
COLUMBIA: ROLE OF OVERSTOREY SHADE
by
Susan M. Nykoluk
B.Sc. (Biology), University o f Northern British Columbia, 1998

THESIS SUBMITTED IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE
in
THE FACULTY OF NATURAL RESOURCES AND
ENVIRONMENTAL STUDIES

© Susan M. Nykoluk, 2002
THE UNIVERSITY OF NORTHERN BRITISH COLUMBIA
February 2002

All rights reserved. This work may not be
reproduced in whole or in part, by photocopy or
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A PPRO V A L

Name:

Susan M. Nykoluk

Degree:

M aster of Science

Thesis Title:

GROW TH OF IN TERIO R SPRU CE AND ATTA CK BY THE
W HITE PINE W EEVIL, PISSO D ES STR O B l (PECK) IN THE
SUB BO REA L SPRU CE ZO N E OF BRITISH COLUM BIA:
ROLE O F O VERSTO REY SHADE

Exam ining Committee:
Chair: Dr. K arin Beeler
Associate Professor, English Program
UNBC

Supervisor: Dr. Chris H aw kins
Associate Professor & Endow ed Chair, Forestry Program
UNBC

Comm ittee M ember: Dr. Russell Dawson
Assistant Professor, Biology Program
UNBC

Comm ittee M ember: Dr. René I. Alfaro
Senior Scientist
Canadian Forest Service

Comm ittee M ember: Dr. Jian W ang
Assistant Professor, Faculty o f Forestry & the Forest Environm ent
Lakehead U niversity

External Exam iner: Dr. John H. Borden
Professor, D epartm ent o f Biological Sciences
Simon Fraser University

D ate Approved:

ABSTRACT

A portion o f an interior spruce plantation, planted in 1989, in the SBSvkl was aeriallysprayed with the herbicide glyphosate in 1996, while the remaining area was left untreated. The
untreated area has an overstorey of paper birch, Betula papyrifera Marsh.. The plantation, 100 km
east o f Prince George, was surveyed for attack by the white pine weevil, Pissodes strobi (Peck),
and tree growth was measured. Attack rates on spruce were markedly lower in the untreated, or
control, portion o f the plantation compared to the herbicide treated area for 2000 and 2001. Mean
spruce, Picea glauca (Moench) Voss x Picea engelmannii Parry ex Engelm, height was 0.85 m
greater in the control compared to the treated area in 2001. There was no difference in diameter at
breast height. Spruce trees growing with birch had better form than trees growing in the open.
Paper birch at a maximum of 3500 stems per hectare (sph) did not impede the growth o f spruce.
Two experiments were established with interior spruce seedlings, and artificial shade to
determine effects o f light on the behaviour o f weevils. In five open pollinated families of spruce in
2000, weevils oviposited lower on the terminal leader on trees under shade. However, overall
attack success was unrelated to shade treatment or ranking of resistance. During 2001, older
propagules (emblings) produced by somatic embryogenesis (SE) were used. Overall success of
attack was unrelated to shade, and there was no relationship between total number o f oviposition
punctures and shade treatment. Shade level may have affected oviposition behaviour but the
spectral properties o f artificial and natural shade are different and may influence the behaviour of
weevils. Resistance to attack by weevils in unshaded SE clones followed original resistance
rankings o f the parent trees.
Findings suggest that overstorey shade created by birch reduces attack by weevils on
spruce, without reducing the rate of growth or form o f interior spruce. Further studies are needed to
determine whether this relationship is specific to paper birch, or generalized to all broadleaf
species.

Ill

TABLE OF CONTENTS

Abstract...................................................................................................................................... ii
Table of Contents...................................................................................................................... iii
List of Tables.............................................................................................................................. v
List of Figures.......................................................................................................................... vii
Acknowledgements.................................................................................................................viii
Chapter 1. Introduction and Review of the Literature.............................................................. 1
1.1 Introduction..............................................................................
1
1.2 Taxonomy and Life Cycle of Pissodes strobi.....................................................................3
1.3 Distribution of P. strobi and Host Trees................
5
1.4 Control Methods - Past and Present.................................................................................... 7
1.4.1 Mechanical Control................................................................................................ 7
1.4.2 Chemical Control.................................................................................................... 7
1.4.3 Biological Control using Natural Enemies............................................................8
1.4.4 Genetic Resistance.................................................................................................. 9
1.4.5 Silviculture.............................................................................................................11
1.5 Economic Significance.......................................................................................................15
1.6 Study Objectives.................................................................................................................16
Chapter 2. Impacts of Paper Birch Overstorey on the growtii of spruce and attack by
the white pine weevil at Sinclair Mills, BC................................................................17
2.1 Introduction.........................................................................................................................17
2.1.1 Objectives..............................................................................................................18
2.1.2 Stand H istory................ ......................................................................................18
2.2 Methodology.......................................................................................................................19
2.2.1 Sampling and Growth........................................................................................... 19
2.2.2 Data Logger.......................................................................................................... 20
2.2.3 Leader dissections and parasite identification.................................................... 21
2.2.4 Light measurements - Ceptometer.......................................................................22
2.2.5 Light measurements - Plant Canopy analyzer - Leaf Area Index (LAI)..........23
2.2.6 Light measurements - portable spectroradiometer (Li 1800)............................. 23
2.3 Results.................................................................................................................................23
2.4 Discussion...........................................................................................................................34
2.4.1 Growth of Spruce.................................................................................................. 34
2.4.2 Attack on Spruce by Weevils...............................................................................35
2.5 Conclusions........................................................................................................................ 38
Chapter 3. Open pollinated interior spruce families and resistance to white pine weevil
under varying degrees of shade..................................................................................39
3.1 Introduction........................................................................................................................ 39
3.2 Methodology...................................................................................................................... 39

IV

3.2.1 Analyses................................................................................................................ 41
3.3 Results................................................................................................................................ 41
47
3.4 Discussion........................................................................
3.5 Conclusions........................................................................................................................ 49
Chapter 4. Environmental factors affecting behaviour of weevils on interior spruce
clones produced by somatic embryogenesis..............................................................50
4.1 Introduction........................................................................................................................ 50
4.2 Methodology...................................................................................................................... 51
4.2.1 North Willow....................................................................................................... .51
4.2.2 Upper Fraser .................................................................................................... 53
4.2.3 Assessments.......................................................................................................... 53
4.2.4 Upper Fraser - 8 block survey..........................
54
4.2.5 Statistical Analyses............................................................................................... 54
4.3 Results.................................................................................................................................55
4.3.1 North Willow........................................................................................................ 55
4.3.2 Upper Fraser, Weevil-Seeded Blocks..................................................................63
4.3.3 Upper Fraser - 8 block survey.............................................................................68
4.4 Discussion.......................................................................................................................... 70
4.4.1 Growth o f Spruce and incidence o f attack by weevils.................................................. 70
4.4.2 Artificial Shade and Overstorey..................................................................................... 70
4.4.3 Bud development of Spruce........................................................................................... 72
4.5 Conclusions.........................................................................................................................73
Chapter 5. Conclusions and Recommendations......................................................................74
5.1 Summary and integration of major findings.....................................................................74
5.2 Experimental benefits, design and liabilities.....................................................................76
5.2.1 Sinclair Mills......................................................................................................... 77
5.2.2 Pass Lake.............................................................................................................. 77
5.2.3 North Willow........................................................................................................ 78
5.3 Recommendations.............................................................................................................. 78
Literature Cited.........................................................................................................................80
Appendix I. Data Logger Programs........................................................................................90
A. 2 IX Micrologger program for Sinclair Mills 2001 ................................................ 90
B. 21X Micrologger program for Pass Lake 2000...................................................... 93
C. 21X Micrologger Program for North Willow 2001................................................ 96
D. Quantum sensor calibration details..........................................................................98
Appendix II. Equipment details and Considerations............................................................100
A. Li-1800 Portable Spectroradiometer...................................................................... 100
B. Ceptometer...............................................................................................................100
C. LAI-2000 Plant Canopy Analyzer.......................................................................... 101

LIST OF T A B L E S

Table 2.1 Mean (standard error) stems per ha for control and treated areas at Sinclair
Mills in May 2001.........................................................
.25
Table 2.2 Mean dbh cm of spruce in control and treated stands in 1999,2000 and 2001 ....25
Table 2.3 Repeated measures analysis in GLM, results for height, dbh and HDR (height
to diameter ratio) in response to fixed effects sources identified in a) between
subjects and b) within subjects...................................................................................26
Table 2.4 Mean height of spruce m in treated and control stands 1999-2001.......................26
Table 2.5 Mean diameter and height increment of spruce in 2001 for treated and control
stands........................................................................................................................... 27
Table 2.6 M Mean, minimum and maximum height and dbh of birch in 1999,2000 and
2001............................................................................................................................. 28
Table 2.7 Mean yearly rates of attack by weevil on spruce (percent of total sample trees
attacked by weevils, resulting in death o f leader) in control and treated plots
28
Table 2.8. Table 2.8 Trees in control and treated area with good, moderate and poor
form and significant difference between each area by form class based on Chisquare analysis............................................................................................................ 29
Table 2.9 Mean light ratio (tree/open) received at leader level, before* and after
deciduous leaf-out in control plots.............................................................................29
Table 2.10 Comparison o f mean number o f diptera (predators) and parasites dissected
ft"om leaders in control and treated areas in 2001..................................................... 31
Table 2.11 Number of adult weevils emerging from leaders clipped in control and
treated areas during 2001..............................................
32
Table 2.12 Mean number o f live weevils, predators and parasites dissected from leaders
clipped in control plots in 2000; shade, partial shade and open in 2000..................32
Table 3.1 Selected families showing original white pine weevil resistance ranking,
breeding value, and location of original plus-trees and successful weevil attack
in 2000............................................................................... i........................................ 40
Table 3.2 Mean height (cm ±SE) of 30 spruce trees from each of five families at Pass
Lake in 1999,2000 and 2001.....................................................................................42
Table 3.3 Repeated measures analysis of variance results for height in 1999,2000 and
2001, in response to resistance, shade treatment and weevil seeded trees (fixed
effects) sources identified in a) between subjects and b) within subjects................42
Table 3.4 Analysis of variance for girth (leader basal diameter) in 1999 between
Resistance (family), shade treatment and weevil seeded trees and their
interactions.................................................................................................................. 43
Table 3.5 Analysis of variance for leader basal diameter in 2000 between Resistance,
shade treatment and weevil seeded trees and their interactions............................... 43
Table 3.6 Mean leader diameter (mm ±SE) in 1999 and 2000 for 30 spruce trees from
each of the five families sampled at Pass Lake......................................................... 44
Table 3.7 Kruskal-Wallis test statistic and significance for non-parametric tests
between number of successful attacks and resistance, shade and oviposition
pattern (category) and resistance and shade treatment..............................................45
Table 3.8 Number of trees in each shade level per oviposition category, showing
significant effects of shade on oviposition................................................................46

VI

Table 4.1 Growth and resistance ranking (Hawkins 1998) for SE clones from original
173 parents’ ranked.....................................................................................................51
Table 4.2 Repeated measures analysis of variance results for height in 2000 and 2001,
for clone, shade treatment and weevil seeded trees and their interactions at
North Willow, sources identified in a) between subjects and b) within subjects. ...55
Table 4.3 Mean height (cm) for clones 1-1026 and 107-1930 at North Willow; mean
overall, mean of successfully attacked trees in 2001 and unsuccessfully
attacked trees in 2001 for 2000 and 2001.................................................................. 56
Table 4.4 Height increment' (cm) for clones 1-1026 and 107-1930 at North Willow.......... 56
Table 4.5 Analysis of variance results for leader basal diameter (2000 leader) in May
2001 at North Willow................................................................................................. 57
Table 4.6 Analysis of variance results for leader basal diameter (2001 leader) in August
2001 at North Willow................................................................................................ 57
Table 4.7 Kruskal-Wallis test for significance results between shade treatments for
distance between the tip of the terminal and the lowest oviposition puncture for
each sampling date for clones 1-1026 and 107-1930 at North Willow a)between
three shade treatments and b)-d) Mann Whitney tests between each shade
treatment..................................................................................................................... 59
Table 4.8 Mann-Whitney results showing differences between clones 1-1026 and 1071930 at North Willow, for bud development; leaders (LD) and first whorl
lateral (LAT)............................................................................................................... 62
Table 4.9 Table 4.9 Repeated measures analysis o f variance results for height in 2000
and 2001, for clone and weevil seeded trees and their interactions at Upper
Fraser, a) between subjects and b) within subjects............................
64
Table 4.10 Mean height (cm) for trees of clones U284 and J974 in 2000 and 2001 at
Upper Fraser
;..................................................................................................... 64
Table 4.11 Height increment (cm) for SE clones U284 and J974 in 2000 and 2001 at
Upper Fraser................................................................................................................64
Table 4.12 Analysis o f variances results for leader basal diameter (2000 leader) in May
2001 and leader basal diameter in August 2001 (2001) leader at the Upper
Fraser.......................................................................................
65
Table 4.13 Table 4.13 Mean number of oviposition punctures for clones U284 and
6J974 at Upper Fraser.................................................................................................65
Table 4.14 Mean number o f predators and parasites and weevils emerged from U284 at
Upper Fraser................................................................................................................66
Table 4.15 Differences between clones J974 and U284 for bud development, leaders
(LD) and first whorl lateral (LAT) using Mann-Whitney non-parametric
analysis........................................................................................................................ 67
Table 4.16 Height (cm ±SE) in 2000 and 2001, height increment (cm ±SE) 2001 and
percentage of trees attacked by weevils historically, in 2000 and in 2001 for
Upper Fraser blocks; Feltons Nursery (PL) and Green Timbers Nursery (GT)
using clone U 185 and seedlot 6864....................................................................
68
Table 4.17 Repeated measures analysis of variance results for height in 2000 and 2001,
for nursery, percent clone o f U185 and their interactions at Upper Fraser, a)
between subjects and b) within subjects.................................................................... 68

vil

LIST OF FIG URES

Figure 2.1 Sinclair Mills block layout and sample plot locations.......................................... 19
Figure 2.2 Number of spruce and birch stems per ha in control (un-treated) and number
of individual attacks by weevils in 2000 and 2001 in sample plots 1-17. Trees
attacked by weevils were classified as either successful or unsuccessful................24
Figure 2.3 Mean number of spruce and birch stems per ha in treated and number of
individual attacks by weevils in 2000 and 2001 in sample plots 1-15. Trees
attacked by weevils were classified as either successful or unsuccessful................24
Figure 2.4 Leaf area index (LAI) for control plots 1-6 and 9-12 taken on June 12 and
13,2001.......................................................................
30
Figure 2.5 Photosynthetically active radiation (PAR) received in 2001 from May 10Septermber 10 (JD 125- 253)..................................................................................... 31
Figure 2.6 Figure 2.7 Light transmission in W/m^’ by wavelength in plot 4, for trees in
the open (a) and in shade (b) on June 1 ,2000; between 0956-1030........................33
Figure 3.1 Mean light intensity (PAR) for each shade treatment (light and heavy) and in
the open at Pass Lake for the May-July 2000 period............................................... 44
Figure 3.2 Energy of light by wavelength for three light treatments, June 1,2000 11:00
at Pass Lake....................................................................................... ;....................... 45
Figure 4.1 Mean oviposition punctures recorded on each sampling date for clones I1026 and 107-1930, and accumulating degree-days above 5°C by sampling
date at North Willow. May 17-July 17,2001 (JDI37-198)......................................58
Figure 4.2 Mean oviposition punctures recorded on trees of clone 1-1026 by sampling
date for each shade treatment (Open, Light, Heavy) at North Willow. May 17July 17,2001 (JD137-I98)...........
58
Figure 4.3 Mean oviposition punctures recorded for trees o f clone 107-1930 by
sampling date for each shade treatment (Open, Light, Heavy) at North Willow.
May 17-July 17,2001 (JD137-198)...........................................................................59
Figure 4.4 Mean Bud-flush classes of leaders (LD) and laterals (LAT) for clones 11026 and 107-1930 at North Willow over 8 weeks: May 17-July 3 2001...............62
Figure 4.5 Mean daily light intensity (PAR) under shade treatments and in the open at
North Willow site, 2001............................................................................................. 63
Figure 4.6 Mean oviposition punctures by sampling date for Clones U284 and J974 at
Upper Fraser, calculated by mean difference in weekly oviposition markings
per sampling date. May 24-July 3,2001 (JD144-198)...............
66
Figure 4.7. Mean Bud-flush classes o f leaders (LD) and laterals (LAT) for clones U284
and J974 at North Willow over 8 weeks: May 24-July 17 2001............................ ..67

vin

ACKNOWLEDGEMENTS

I wish to thank my supervisor, Dr. Chris Hawkins, for financial support during my degree,
as well as for his many comments regarding the experimental design, analysis and writing o f this
thesis. I would also like to recognize all members of my committee for their time assistance with
this project. I wish to acknowledge Dr. Rene Alfaro for his advice on the weevil-seeding
experiments and for suggestions regarding this document. Thanks also go out to Dr. Jian Wang for
his suggestions on the Sinclair Mills study as well as recommendations for this document, and Dr.
Russ Dawson, for his helpful comments in editing this thesis.
A very special thank you must go to the summer field assistants who worked during some
point on one or several of the studies. Without their help much would not have been accomplished,
and I would like to mention the following for their assistance: Jennifer Lange, Tracy Murray, Anne
Cole, Marcin Partyka, Patience Byman and Kirstin Cam pbell. I wish to also thank Nicole Wilder
for scheduling the field staff and performing many other administrative duties.
Recognition must be given to Tony Letchford, Ministry o f Forests British Columbia, for
his invaluable service with field equipment, and to Bob Richards, Forest Service - Prince George
District, for providing information and maps for the Sinclair Mills sites.
I would like to thank my parents for their understanding and support throughout the course
of my degree. Finally, I would like to thank the many graduate students who helped with collecting
weevils and various other tasks, and who were a source of companionship during my studies at
UNBC.

CHAPTER 1

Introduction and Review o f the Literature

1.1 Introduction
The white pine weevil, Pissodes strobi (Peck) (Coleoptera: Curculionidae), is a serious
pest o f many young spruce plantations in the British Columbia because it destroys the terminal
shoot o f young spruce trees causing stem defects and reducing height growth (Silver 1968; Alfaro
1982). The Sub Boreal Spruce (SBS) and Interior Cedar Hemlock (ICH) Bigeoclimatic zones
(Meidinger et al. 1991) are considered to be high hazard zones for weevil infestation with an
estimated 400,000 ha at risk in the central British Columbia interior based on degree-day
requirements for larval development (Spittlehouse etal. 1994). The SBS and ICH are characterized
by long cold winters and relatively warm moist, but short summers (Meidinger et al. 1991; Coates
et al. 1994). The weevil is thought to be the most destructive pest o f second-growth spruce in
British Columbia (Alfaro and Borden 1985). At present, after regeneration, licensees have the legal
obligation o f ensuring their plantations reach a free-growing status within an allotted time period
(BC Ministry o f Forests 2000). These recommendations may however, have negative effects
regarding rates o f weevil-infestation and recovery o f spruce after attack. Species o f deciduous­
brush are removed from plantations to allow crop trees to grow without competition. In doing so,
favourable conditions are created for weevil infestations due to increased light and temperature
(Lanier 1983; Alfaro etal. 1994; Alfaro 1998).
Historically, weevil infestations have been o f concern mainly in coastal British Columbia
on Sitka spruce, Picea sitchensis (Bong) Carr.* This is largely due to the activity o f reforestation
occurring in this region. However, recent evidence has shown that white pine weevil may become

' All tree names and authorities taken from: Farrar, J.L. 1995. Trees in Canada. Fitzhenry & Whiteside Ltd.
and the Canadian Forest Service. 501pp.

just as damaging in the interior o f BC as much o f the region has been replanted over the past 20
years (Alfaro 1998). It is difficult to determine the total area at risk to weevil infestation.
Previously, estimates o f 34,000 ha were said to be at risk in the Prince George Forest District in
1994, with an additional 100,000 hectares reaching susceptible levels within the following decade
(Hall 1994). Hazard levels are based upon biogeoclimatic subzones and elevations, which allow for
the required degree-days needed for insect development from larva to adult (Spittlehouse et al.
1994; Taylor 1997). Temperatures relating to these subzones are generally recorded from airport
weather stations and are somewhat limited in their scope in that they cannot accurately represent
the variety of microclimatic conditions that occur in a forest or stand (McIntosh 1997).
Previous studies (Cozens 1983; McLean 1994; Taylor etal. 1996) have shown that a
deciduous overstorey reduces attack by weevil on spruce. In addition, shade from deciduous
overstorey may positively affect the post-attack recovery o f interior spruce trees by allowing the
terminal shoot or a lateral to take over and resume a normal growth pattern and apical dominance
much sooner than in the open. Return to a normal pattern o f development allows trees to resume
growth at more predictable rates, reducing losses in height. This ultimately translates into greater
gains in volume and wood quality than would be the case with slow recovery in the open. There
has been much evidence showing that conifers grown with deciduous species show greater
resistance to attack by weevil (Stiell and Berry 1985; McLean 1994; Taylor and Cozens 1994).
Past research focused on the role of physical factors such as temperature (Sullivan 1959;
Sullivan 1960; McMullen 1976), and light (Sullivan 1961; VanderSar and Borden 1977) to explain
why overstorey mitigates attack by weevil. These and many other factors, may interact to reduce
attack by weevils under shaded conditions. This thesis investigates some o f these factors to help
determine the mechanism by which attacks by the white pine weevil, at both the tree- and standlevel on interior spruce, Picea glauca (Moench) Voss x Picea engelmannii Parry ex Engelm., are
reduced under shade.

1.2 Taxonomy and Life Cycle of Pissodes strobi
The white pine weevil was first recognized as a destructive pest of the dominant shoot of
the Weymouth pine (eastern white pine), Pinus strobus L. in 1817 by W.D. Peck, Professor of
Natural History and Botany at Harvard University (Belyea and Sullivan 1956). Hopkins (1907,
1911), who first described a detailed life history of this insect, originally recognized 30 North
American species in the genus Pissodes. The genus Pissodes (Langor 1998) now contains 29
described species in North and Central America, all o f which are associated with conifers. P. strobi
is considered to be the most damaging o f the genus Pissodes, but other insects within it include: P.
terminalis Hopping, the lodgepole pine terminal weevil, P. nemorensis germar, P. schwarzi
Hopkins, which attack the boles o f weak and dead trees and P.fasciatus LeConte which has been
suspected in the spread o f fungal diseases o f conifers (Langor 1998).
Classification o f Pissodes strobi was originally based upon insect morphology and the
association with host-trees. In British Columbia, species were previously called Pissodes sitchensis
Hopkins, Pissodes engelmcmii Hopkins, and Pissodes strobi (Peck) in accordance with the insect’s
locale and host tree (Hopkins 1911; Manna and Smith 1959). Later this evidence was refuted
through breeding experiments (Manna and Smith 1959; Smith 1962; Smith and Sudgen 1969),
physiological evidence (VanderSar et al. 1977) and protein electrophoresis (Phillips and Lanier
1985). Thus, all three populations were considered to be o f the same species. More recently,
randomly amplified polymorphic DNA (RAPD) marker studies have indicated three separate
genetic subspecies of P. strobi in British Columbia and one subspecies east o f the Rocky
Mountains (Lewis 1995; Lewis et al. 2000). Although evolutionary divergence has occurred
between populations, all subspecies are currently known by the binomial, Pissodes strobi (Peck).
Pissodes strobi produces one generation per year and has a maximum life span of four
years (McMullen and Condrashoff 1973; Kline and Mitchell 1979; Wood and McMullen 1983).
Adults emerge from hibernation in the spring when snow has melted fi’om the base o f trees, and the
forest floor where they overwinter has warmed to 6°C or greater (Sullivan 1959). Adults then move

up the stem o f the host tree to begin feeding on shoots (Sullivan 1960). Stevenson (1967) observed
that feeding by weevils occurred on the uppermost portions of stems on the north side o f dominant
leaders. Weevils are diecious and mating generally occurs on the tree's terminal shoot (Hopkins
1911). It is possible that pheromones play a role in attracting weevils during breeding; however, no
pheromone has been definitively identified (Booth and Lanier 1974; Phillips and Lanier 1986). Egg
laying, or oviposition, by females occurs under or in the bud o f the terminal branch from the
previous year. Frequency and distribution of eggs has been shown to be affected by shade for
insects feeding on white pine (Sullivan 1961). Eggs are laid in feeding punctures, occasionally in
groups of two or three (Gara et al. 1971) but are usually single. As many as five eggs have been
reported in a single puncture (McMullen and Condrashoff 1973). In a single leader, as many as 200
eggs may be laid (Wallace and Sullivan 1985) although a mean o f 64 eggs are laid in Sitka spruce
(Silver 1968). Females tend to lay all their eggs in a single leader (Stevenson 1967; Silver 1968).
The fecundity o f weevils remains constant throughout their life span (Stevenson 1967; Gara et al.
1971; McMullen and Condrashoff 1973). This was confirmed by Trudel and Lavallée (2001) who
showed that two-year old females produced as many eggs and oviposited at the same rate, on white
pine, as did one-year old weevils. Eggs o f P. strobi are oval, white-opalescent and measure 1.0 mm
by 0.5 mm (Wood and McMullen 1983; Tumquist and Alfaro 1996). After the eggs are laid, they
are covered with a dark-coloured fecal plug. Gara et al. (1980) hypothesized that the fecal plug
served the purposes o f identification o f an egg-containing cavity to other weevils and protection
against egg predation by other species.
Larvae begin feeding as soon as they hatch, which occurs approximately two weeks after
the eggs are laid (Belyea and Sullivan 1956). They feed in a ring and move downwards as a group
while feeding on the phloem tissue. Larvae feed for about five to six weeks, by which time infested
leaders are killed (Belyea and Sullivan 1956). The new terminal shoot o f the tree eventually turns a
yellow-redish colour and starts to droop because the downward feeding of the larvae on the phloem
gradually severs the xylem tissue (Mitchel etal. 1990). The tree’s needles turn red in late summer

or early fall and eventually fall off in subsequent years. The larvae go through four instars, which
are identified by the size o f the head capsule (Silver 1968). Development for an individual larva to
the pupal stage takes about 34 days, although there is much variation in dates between oviposition
and hatching for individual larvae (Stevenson 1967). In mid-summer, larvae form pupal chambers
or chip-cocoons out o f xylem fibres. In stems less than 1.9 cm in diameter the larvae almost always
pupate in the pith without chip-cocoons (Stevenson 1967). Pupation takes approximately two
weeks after which the new adults emerge or stay within the stem for another two weeks
(MacAloney 1930). Adults emerge in late summer or early fall after chewing holes through the
bark (Stevenson 1967). There is generally one emergence hole per weevil (Nealis 1998). Adult
weevils are approximately 0.5 cm long with a long curved snout and cylindrical body. The elytra
contain patches of light brown or grey scales (Belyea and Sullivan 1956).
Weevils emerging in the fall tend not to fly due to flight muscles being undeveloped
compared to spring adults (Stevenson 1967). Stevenson (1967) showed this using 136 newly
emerged fall adults. After subjecting half to a cold treatment o f 2.22°C (36“F) and the other half to
warmer temperatures (I8.33°C-22.22°C, 65-72°F) for 48 days he tested their flight response. Only
weevils that had been subjected to cold temperatures were capable of flight. Dissections revealed
undeveloped flight muscles in individuals that had not been subjected to cold treatment (Stevenson
1967). Belyea and Sullivan (1956) noted that adult weevils emerging in the fall do not mate and
oviposit at this time but are limited to feeding on branches. When temperatures drop below 5°C
weevils move to the duff layer of the forest floor, usually under the tree from which they emerged,
and find hibernation sites (Sullivan 1959). In the Prince George region, this usually occurs in late
September or early October (Cozens 1983).

1.3 Distribution o f P. strobi and H ost Trees
Pissodes strobi is native to North America and ranges from the Pacific to Atlantic coast, as
far north as 60“N in the Yukon and Great Slave Lake in the Northwest Territories (Brown et al.

1960), and as far south as central Colorado in the west and northern Georgia in the east (Hopkins
1911; Humble et al. 1994; Langor and Sperling 1995). In the east, P. strobi has mainly been found
in the Southern boreal forest o f Ontario, Quebec and the Maritime provinces o f New Brunswick,
Nova Scotia and Prince Edward Island (Humble et al. 1994). VanderSar et al. (1977) showed that
P. strobi from the Pacific Coast fed on white pine as readily, as on spruce, but P. Strobi from the
East did not feed on spruce from the west. From this he concluded that P. strobi probably
originated in the East (VanderSar et al. 1977).
In eastern Canada, the weevil is a pest primarily to eastern white pine, Pinus strobus L. and
the exotic Norway spruce, Picea abies (L.) Karst., while in the west it primarily attacks Sitka,
Picea sitchensis (Bong) Carr., white, Picea glauca (Moench) Voss, Engelmann Spruce, Picea
engelmanii Parry, and interior spruce, Picea glauca (Moench) Voss x Picea engelmannii Parry ex
Engelm (Belyea and Sullivan 1956). Pines are the primary hosts in the Maritime Provinces. There
are several other North American trees that are also attacked by P. strobi but usually not at
epidemic levels (Humble et al. 1994). The following species o f spruce have also been shown to
host the weevil: black spruce, Picea mariana (Mill.) B.S.P., Parry, red spruce, P. rubens Sarg, and
Colorado spruce, P. pungens Engelm. (Humble et al. 1994). Other pines which have been shown to
host the weevil include jack pine, Pinus banksiana Lamb., lodgepole pine, Pinus contorta Dougl.
Ex Loud. var. latifolia Engelm., red pine, P. resinosa Ait., Austrian pine, P. nigra Am., and two
exotic pine species: Mugho pine, P. mugo Turra, and Scots pine, P. sylvestris L. (Humble et al.
1994).
Epidemic levels, greater than 20% of trees attacked by weevils in a single year, on Sitka
spmce in some coastal regions has led to shifting planting preferences to entirely different species
(Wallace and Sullivan 1985). The only coastal region o f British Columbia that has been unaffected
by the weevil so far, is the Queen Charlotte Islands, where the insect has never been reported
(Humble et al. 1994; Tumquist and Alfaro 1996).

1.4 Control Methods - Past and Present
Many methods have been used in an attempt to control the weevil and lessen the damage
and financial losses incurred by P. strobi. Some of these methods were costly, while others were
potentially detrimental to the environment. A brief summary o f these methods follows.

1.4.1 Mechanical Control
Mechanical control of weevils by clipping attacked leaders before adult emergence has
been tried but has largely proven to be costly and ineffective in BC. Peck first recommended this
mode of control in 1817 (Belyea and Sullivan 1956). Before chemical insecticides were used,
leaders were clipped and burned (de Groot and Kelson 1994). Heppner (1989) conducted a clipping
trial on Sitka spruce, which was partly successful. McLean (1989) found high numbers o f predators
in leaders and noted that leader clipping removes the beneficial insects, which overwinter in the
leaders. Rankin and Lewis (1994) calculated that the mean cost for clipping was $250/ha. They
placed infested leaders in screened pails to allow for the escape o f predators and parasites but to
keep adult weevils inside. Although leader-clipping proved to be successful in reducing damage it
is not economically feasible on a large operational scale.

1.4.2 Chemical Control
A complete historical description on the use of chemical control to fight weevil outbreaks
since 1886 is given by de Groot and Kelson (1994). At the turn o f the century, copper acetoarsenite wash, known as “Paris Green” was applied to susceptible trees. Since then, other chemicals
including soap mixed with Paris Green, lime sulphur, shale oil soap, sulphur, lead arsenate and
kerosene have been tried. During the 1920’s and 1930’s silvicultural practices began to
overshadow chemical control but by the 1950’s, after successful field trials o f DDT,
dichlorodiphenyltrichloroethane, it was thought that a solution to weevil outbreaks had been found.
Aerial control trials with DDT were first undertaken in Ontario 1957 and again from 1961 to 1973.

8

Use of insecticides peaked from the mid-1960’s to early 1970’s. Some o f these included
malathion, carbaryl, Zectran, Bidrin, heptachlor, dimethoate, Metasystox-R, Guthion, endosulfan,
and dieldrin (de Groot and Helson 1994). In the early 1970’s, concern for the impact o f insecticides
on the environment became more prominent. Many of the above-listed chemicals have since been
banned for use in North America. Systemic spray applications have also been tested in ground
spraying trials as well as soil applications aimed at overwintering populations (de Groot and
Helson 1994). Bradbury (1986) also applied Metasystox-R to determine if it had any effect on
larvae inside the leader. He found that four applications at 10-day intervals offered complete
protection of the leader. Fraser and Heppner (1993) also reported that stem implants with acephate
were effective in controlling weevils on Sitka spruce.
Due to the many constraints o f using insecticides it was concluded that chemical
application was best used in high-value plantations where other management practices are
impractical or inadequate. Currently, insecticides for controlling attacks by weevil are considered
inappropriate in moderate to large plantations due to potential damaging environmental effects (de
Groot and Helson 1994).

1.4.3 Biological Control, using Natural Enemies
Although there have been relatively few studies on biological control o f weevils, previous
studies (Stevenson 1967; Hulme et al. 1987; Hulme and Harris 1988) have shown that many
parasites and predators associated with Pissodes strobi may be effective for population control.
Nealis (1998) stated that the relationship among predators and parasitoids, may be as much of a
factor in rates o f attack as physical and biotic changes associated with the growth o f host trees.
Most natural enemies are either dipteran predators, or hymenopteran parasitoids. In a study of
weevil populations in jack pine in Ontario, there was a strong negative relationship with the
dipteran parasite Lonchaea corticis Taylor and weevil emergence (Nealis 1998). Without natural
enemies, weevil populations could be as much as three times greater (Nealis 1998). Stevenson

(1967) found that L. corticis destroyed about 20% o f the larvae and pupae in his study. Predation
by birds may contribute to reducing populations o f weevils (Taylor 1929; Bellocq and Smith 1994),
although rates o f predation may vary depending on the overstorey species (Taylor 1997) and the
abundance o f weevils (Nealis 1998).
Hulme (1994) thought that the braconid wasp, Allodorus crassigaster Provancher, was a
potential insect to use for biological control o f the weevil because of its ability to kill a large
proportion o f the brood o f weevil larvae. Female wasps lay their eggs in the eggs o f weevils by
inserting their oviopositor through the fecal cap left after egg laying by the weevil. The larvae of
the wasp then develop to the first instar inside the weevil egg capsule. When the weevil-larva
begins to pupate the larva o f the wasp molts to the second instar and begins to feed on the weevil
larva from the inside (Hulme 1994). At this time, biological control o f the weevil is not used as a
management practice.

1.4.4 Genetic Resistance
Genetic resistance o f a tree to attack by white pine weevil is varied as it often involves the
combination o f several traits. Because the genetics o f P. strobi vary by population and by region,
what may act as a resistance mechanism in one genotype o f spruce may not act as a resistance
mechanism in another. Combined with the interactions of differences in site, changing climate, and
fluctuating populations, determining genetic resistance o f a species of tree is sometimes difficult.
The processes that lie beneath particular defence mechanisms may not be active all the time, but
may be triggered in the spring by environmental factors (Alfaro 1997). The favoured host
individuals of P. strobi are the most rapidly growing sapling and pole-sized trees o f either spruce or
pine in the stand (Lanier 1983). King et al. (1997) showed that weevils preferred fast growing
interior spruce trees as hosts, but also showed that fast growing families had high levels o f genetic
resistance to attack. Hulme (1995) observed that the least-damaged trees in a Sitka spruce
provenance started development o f apical buds earlier than did susceptible clones. He also showed

10

that when the phenology of the clones was delayed, weevils would attack the resistant genotypes.
Subsequently, Alfaro et al. (2000) showed that early development o f buds in Sitka spruce is
sometimes weakly correlated with resistance to weevils.
Genetic variation among families o f spruce with regard to rate of attack and damage has
been found in interior and Sitka spruce (Alfaro 1997). Trees have been regarded as tolerant to
attack if they have the ability to recover from weevil damage (Alfaro and Ying 1990), but are
regarded as resistant to attack if they have the ability to avoid, or fend off, attacks (Mitchel et al.
1990; Kiss and Yanchuk 1991). Variation in genetic resistance has been shown within families of
spruce (Alfaro et al. l996a). In white spruce, the resistant families are typically the fastest growing
trees (Alfaro et al. 1996a; King et al. 1997). Ying (1990) found resistance in at least three
provenances o f Sitka spruce in coastal British Columbia. Within these families he found 15 times
less attack on the resistant families compared to the most susceptible families (Ying 1990).
Resistance to weevil may be due to a combination o f mechanisms. For example, Tomlin
and Borden (1997a) and Tomlin et al. (1996) showed resin ducts, which contain terpenes and high
amounts o f cortical resin acid are important in resistance to weevil. Resin is considered to be a
defensive mechanism o f conifers that deters attack, prevents fungal growth and drowns eggs and
larvae (Berryman 1972). Tomlin et al. (1996) found Sitka spruce trees with very high levels o f acid
in the resin may have a greater capacity to deter feeding or produce resin which is toxic to eggs and
larvae. In addition, foliar terpenes have also been shown as a mechanism o f resistance to weevils in
Sitka spruce (Tomlin et al. 1997). Nault et al. (1999) found that levels o f terpenes or other volatiles
in the leaf or bark o f white and Engelmann spruce were highly correlated within ramets of highly
variable progeny and concluded that the level o f terpenes is not a useful tool for selecting resistant
genotypes.
Alfaro (1995) showed that an induced defence reaction occurred in Sitka spruce after
weevils began feeding and laying eggs. The reaction consisted o f the cambium cells switching from
producing normal tracheids and parenchyma cells, to producing traumatic resin canals that killed

11

eggs and larvae (Alfaro 1995). Tomlin and Borden (1998) found Sitka spruce trees from families
with know resistance responded with faster and with greater intensity than trees from susceptible
families in producing traumatic resin canals. Sahota et al. (1994) proposed that chemicals in the
bark o f resistant spruce could hamper reproduction in female weevils by causing ovarian regression
or inhibition of development.
Although genetic resistance found in host species shows promise, resistance as a control
mechanism may be impeded by the insect’s ability to adapt. Alfaro (1996) found that females
confined to resistant trees oviposited lower in the stem, below the leader, where resin canal density
was reduced due to increased stem diameter, thereby preventing the brood from being drowned.
Use o f resistant stock, such as that produced by somatic embryogenesis technology, promises to be
a valuable tool for pest management but will need to be used with other control methods, such as
silviculture, to minimize the effects o f adaptation by the weevil. Alfaro et al. (1995) suggested a
system of integrated pest management, which incorporates hazard assessment with the planting of
genetically resistant stock.

1.4.5 Silviculture
Using silvicultural methods to mitigate the effects o f weevils essentially involves utilizing
shade to mimic the mitigating effects o f natural forest processes. Infestations o f white pine weevil
are known to have occurred after natural disturbance events such as wildfires (Kimoto et al. 2000).
Silvicultural methods recommend providing overstorey or side shade and using mixtures o f tree
species. Several researchers (Graham 1918; MacAloney 1930) have observed that conifers growing
under deciduous overstorey were subject to lower rates o f attack by weevils compared to their
counterparts growing in the open. Graham (1926) recommended silvicultural systems that provided
shade for young eastern white pines after noting that those growing in the shade, or in high
densities, were attacked less by the white pine weevil than trees o f the same age growing in full
sunlight. MacAloney (1930) concluded that the easiest and most cost-effective way to protect white

12

pine from the weevil was to grow it in a mixture o f tree species that would add value to the final
crop. He also noted that successive thinning treatments would be necessary so that pines would not
be crowded out (MacAloney 1930). Conversely, Pubanz et al. (1999) questioned the use of
overstorey for reducing the damaging effects o f the weevil. Their study o f well-stocked stands on
the Menominee Forest in Wisconsin showed that 87.3% o f eastern white pines in their samples had
an identifiable weevil injuiy (Pubanz et a l 1999). They concluded that volume losses due to attack
by weevil have been overestimated. However, Brace (1972) previously estimated o f weevil-control
could raise the value o f white pine by 25%.
Several studies have shown that trees growing in shaded conditions have lower rates of
attack by weevils than trees growing in the open (Katovich and Morse 1992; McLean 1994; Taylor
and Cozens 1994; Taylor et al. 1996). McLean (1989) studied the effects o f naturally regenerated
red alder, Alnus rubra Bong, in 0.14 ha, on growth and attack by weevils on Sitka spruce. Half of
the site was cleared o f all species and the other half was strip-cleared leaving rows o f alder running
in a north-south direction. Two stock-types o f Sitka spruce were planted in each treatment. The
results after eight years showed that one o f the stock-types maintained similar height growth in
both the open and understory treatment; however, trees growing under red alder had suppressed
diameter growth. The trees growing in the open also had more attacks by weevil. McLean (1989)
also found that there were higher levels o f the dipteran predator Lonchaea corticis Taylor in leaders
infested with weevils growing in the open compared to those growing in the shade. This was
probably due to the fact more food, in the form o f weevil larvae, was available to the predators in
the open compared to the shade. In a follow up study, McLean (1994) showed rates of attack by
weevils to be similar in both understory and open treatments. This was attributed to the clipping of
leaders, which reduced the emerging weevil population and to a treatment o f sewage sludge, which
may have affected their overwintering sites. In a similar study by Taylor and Cozens (1994), side
shade from aspen reduced attack by weevils as much as overstorey shade when the strip cuts ran in
a east to west direction. Their results indicated that up to 6% reductions in levels o f attack by

13

weevils could be expected five years after the strip cut treatment. Attack levels were 21.3% in the
completely brushed area, 14.8% in the side shade treatment and 15.1% in the overstorey shade
(Taylor and Cozens 1994).
Researchers have long sought to determine the role o f shade and its effects on success of
weevils. McMullen (1976) showed that the development of weevils from egg to adult required 785
degree-days above 7.2°C in order for weevils to complete their biological cycle in white spruce
leaders under laboratory conditions. The accuracy o f this estimate was later tested and confirmed
by McIntosh (1997) using internal temperatures o f white spruce leaders. Elevation, through its
effects on temperature, affects the rate o f infestation by weevils (Spittlehouse et al. 1994; Taylor
1997). Therefore the presence o f overstorey that shades the tree’s terminal leader can reduce the
degree-days available for brood development.
Sullivan (1961) also showed that reduced temperature under shade resulted in less
aggregated feeding on white pine. Alternatively, VanderSar and Borden (1977) showed that
weevils have a visual response to Sitka spruce leaders and hypothesized that overstorey trees
disturb this silhouette making it difficult for the weevil to locate suitable host-trees. They also
demonstrated that weevils have a strong physiological response to light, which makes them climb
to the top o f leaders after emerging in the spring. VanderSar (1977) also showed that weevils
emerging in the spring have a strong phototaxis and negative geotaxis. From his laboratory
experiments on excised leaders, he showed that the response to light was the mechanism that
primarily governs female oviposition in the spring after overwintering. Shade, created from
deciduous overstorey has been shown to reduce overwintering success (Harman and Kulman
1969). Shade may also alter the chemical properties o f the leader making them an undesirable host
to weevils (Harman and Kulman 1967). Shade also affects the girth o f a tree making the diameter
o f the leader smaller and less likely to be attacked (Sullivan 1961). In addition, shade may delay
budburst, causing weevils to seek out trees that are further developed, or which are in synchrony
with their spring emergence from overwintering (Hulme 1995, Alfaro et al. 2000). A deciduous

14

canopy also affects the quality o f light by disrupting ultraviolet light, which may be an important
requirement for weevils when responding to light (Droska et al. 1983).
Spacing o f trees may also contribute to reduced attack by weevils. Alfaro and Omule
(1990) found that increased density, or decreased spacing of young trees, reduced attacks by
weevils in Sitka spruce. Their management plan recommended initial spacing o f 2.74 m, which
should then be thinned at 25 years. Reduced attack by weevils as a result o f closer spacing is
thought to be due to reductions in temperature, or possibly side shade (Taylor and Cozens 1994).
Stiell and Beny (1985) showed that side shade from birch reduced the incidence o f attack by
weevil on eastern white pine. They found that strip cuts in a white pine plantation permitted
between 50-70% o f full light, and allowed trees to grow adequately with diminished growth in
height, but remained relatively free from weevil damage (Stiell and B eny 1985). Conversely,
Hawkins (Pers. Comm. 2000) observed that attacks by weevil increased with the percentage of
available stems at narrow spacing in 30-year-old interior spruce plantations growing in the wet cool
(w kl) of the Sub Boreal Spruce Biogeoclimatic zone (SBS).
The availability o f light potentially can affect 1) the growth and phenology o f the tree
(Logan 1962,1969); 2) the insects’ ability to perceive the host (VanderSar and Borden 1977); and
3) the temperature required for mating and brood development (McMullen 1976). Light also affects
secondary factors, which in turn may impact success o f weevils, such as insect predators and
parasites that are influenced by temperature. Juvenile spruce are shade tolerant (Logan 1962).
Logan (1969) showed that 50% reduction o f light did not impede height growth o f white spruce by
did inhibit diameter growth. VanderSar and Borden (1977) demonstrated that weevils preferred
thicker over thinner leaders o f Sitka spruce, which may result from growing under reduced light
conditions. Messier et al. (1999) showed that planting eastern white pine under a hardwood forest
reduced competition and protected the trees against damage from weevils. They demonstrated that
levels between 10 and 66% full sunlight did not impede growth in the first six years but that total

15

height and diameter after six years tended to deeline sharply when there was 30% or more
reduetion o f full sunlight (Messier et al. 1999).

1.5 Economic Significance
Generally, a minimum o f two years growth is lost with each successful attack by weevil
because the current and previous year’s leaders are killed. Cozens (1987) found a 19.5 % re­
attack rate on previously attacked trees in interior spruee plantations. Interior spruce is one of the
two major commercial species for the central interior, especially in the Prince George Forest
District. Since 1984 more than one billion interior spruce seedlings have been planted (Taylor
1997). Most attacks occur in interior spruce stands when they are open grown, between 10-30
years o f age and between 2-20 meters tall (Alfaro 1998). However, in high hazard areas, attacks
can occur as early as three years at heights o f less than 1 m (Hawkins Pers. Comm. 2000).
McMullen et al. (1987) developed a model to simulate population dynamics o f the weevil on
Sitka spruce which predicted a 30% reduction in gross volume with severe attack-rates. Alfaro et
al. (1996b) developed a model to predict volume losses due to attack by weevil called Spruce
Attack by weevil (SWAT) which included reductions in net merchantable volume due to defect
formation, a factor lacking in the earlier model. The SWAT model works with the TASS, Tree
and Stand Simulator, growth and yield model developed by the BC Ministry o f Forests to
forecast growth. SWAT is used to simulate the damage to trees from attack by weevil (Alfaro et
al. 1996b). This model has predicted growth losses between 8-65% in the Prince George Forest
District, depending on the intensity and duration of attack (Taylor et al. 1996).
Large investments have been made in plantations that include planting and vegetation
management activities such as brushing or herbicide application. Current legislation in BC
restricts the amount o f broadleaf species in planted stands to minimum levels. Species such as
paper birch, Betula papyifera Marsh., are considered weed species and are either treated with
herbicide, cut, or girdled to release conifers from competition to meet free-growing requirements

16

(BC Ministry of Forests 2000). For these investments to be gainfully returned, operational
practices for managing attack by weevils need to be incorporated into the free-growing
recommendations. Even if spruce trees appear to fully recover from attack, damage incurred at an
early age has often already resulted in losses in growth, yield and wood quality. Therefore, the
main economic losses incurred from attack by white pine weevil are not realized until time of
rotation, due to delay in the harvest.

1.6 Study Objectives
My main objective was to determine if reduced light levels, or shade, created artificially or
naturally, lowered success by P. strobi on interior spruce trees.
The objective was approached by evaluating the:

1. effects o f deciduous overstorey on attack-rate in a young plantation, containing a large endemic
population o f white pine weevil, and by
2. determining the effects o f artificial shade on attack by weevils on planted seedlings.

17

CHAPTER 2

Impacts of Paper Birch Overstorey on the growth o f spruce and attack by the white pine weevil at
Sinclair Mills, BC

2.1 Introduction
In central British Columbia, susceptibility of interior spruce stands to infestation by white
pine weevil may be increased by current silvicultural practices. These practices are firstly, the
planting o f a single species in large open clear-cuts, and secondly the management practice of
brushing and treating competing vegetation with herbicide to meet Forest Practices Code
guidelines (BC Ministry o f Forests 2000). Clear-cuts may resemble burned areas which occur in
the natural forest (Kimoto et al. 2000). Such areas create conditions that allow weevil-populations
to flourish because they have easy access to a large number o f host terminals, and temperatures are
also elevated for brood development to levels which meet the required 785 degree-days above
7.2°C (McMullen 1976). Spittlehouse et al. (1994) found that daily average temperatures inside the
leader are greater than air temperatures on sunny days and are approximately I°C on average above
air temperatures during the summer months in the interior o f British Columbia. Sieben et al. (1997)
has since revised McMullen’s (1976) formula for calculating temperature in the interior o f British
Columbia by adding 1°C.
It has been hypothesized that removal o f broadleaf competitors to enhance growth of
conifers may result in increased rates o f attack by white pine weevils (Lanier 1983; Alfaro et al.
1994; Alfaro 1998). Changes to the BC Forest Act in 1987 promoted the planting o f large spruce
stands, which must reach a free-growing status 9-15 years after planting (BC Ministry o f Forests
2000). Competition from deciduous overstorey, often compromises diameter growth in conifers
(Gordon and Larson 1968, page 76), as maximum diameter growth occurs in ftill sunlight (Lieffers
and Stadt, 1994; Wright et al. 1998). Therefore, when overtopping brush is removed favourable

18

habitat is created for the weevil. In addition, ground temperature is increased, allowing for snow to
melt earlier and overwintering sites o f weevils to be warmed sooner than sites located under
deciduous cover.

2.1.1 Objectives
My main objectives o f were 1) to compare attack levels o f weevil in control and treated
stands of interior spruce four years after vegetation removal with glyphosate in the treated stand
and 2) to follow weevil-attack rates in both stands over 2 years. In doing so, it would be determined
whether removal of mainly paper birch has an impact on rates o f attack by weevil and growth
variables of interior spruce. Secondary objectives were to quantify differences in light and
temperature between open and shaded spruce trees.

2.1.2 Stand History
The study plantation is located approximately 100 km north east o f Prince George
(Latitude: 54°01' N, Longitude: 121°41' W) at 700 m elevation. It was harvested in the winter of
1987-1988 and broadcast burned in June 1988. The plantation is in the Sub-Boreal spruce very wet
and cool (SBSvk 01) subzone (Meidinger and Pojar 1991). The mean annual temperature ranges
fi-om 1.3 to 4°C. Annual precipitation ranges from 990 to 1635 mm with only a third falling during
the growing season. White pine weevil can have a severe impact on spruce plantations in the
SBSvk. In 1989, 77.7 ha o f the area was planted with interior spruce (2+1 PBR) seedlot 29164 at
2.5 m spacing, and 14.3 ha was planted with lodgepole pine (1+0 PSB) seedlot 14901 at similar
spacing. The plantation was grazed with sheep, for brush control, in the summer o f 1992. In July
1996,24.1 ha o f the plantation were treated with the herbicide glyphosate by aerial application to
remove competing paper birch, Betula papyrifera Marsh. The remaining portion of the block was
not treated as competing vegetation was not considered to be a threat to the spruce at that time.

19

2.2 Methodology
2.2.1 Sampling and Growth
Fifteen, 3.99 m radius plots were systematically selected on 3 transect lines at 25 m
intervals in the herbicide treated area o f the block (Figure 2.1). Seventeen 5.64 m radius plots were
selectively sampled in two regions in control area (Figure 2.1). Larger plots were used in the
control area, because the birch was not uniformly dispersed, and therefore larger plots were
required to include spruce trees that received different light intensities at the leader within the same
area. When the time plots were installed, psuedoreplication was not considered to be an issue as
growing environments were similar in both areas (Hawkins and Draper 1991; and Hawkins et al.
1996).

'Treated

oooo

OOOO0

Control

Legend
" 3.99 m plots
* 5.64 m plots
400

400

800
Meters

Figure 2.1 Sinclair Mills block layout and sample plot locations.

20

All naturally regenerated spruce, five in total, and all located in the control area, were removed
from the data set. In total there were 193 planted spruce in the control area and 101 in the treated
area that were measured for 1) height using a height pole, 2) diameter at breast height (dbh, 1.3m)
using a diameter tape, 3) successful attack by weevil (yes or no), defined as leaders killed from
attack by weevil in which broods developed (exhibited by shepherds crook or wilted and dying
leader), and form. Form was quantified as O=good, form that would produce a quality butt saw-log;
l=minor defect, such as multiple leaders (but not stag-heads) above the first 2 m o f the tree but no
visible fork or crook in the stem; or 2 =major defect, such as a fork, major crook or stag-head,
above 30 cm and below 2 m from the base o f the main stem that is seriously impeding growth.
Form data were analyzed using Chi-square analysis. All deciduous species in the control plots were
measured for height and diameter at breast height. Measurements were repeated in 1999, 2000 and
2001 in the control area and in 2000 and 2001 in the treated area. Data were analysed for
differences in height, diameter and diameter increment, between the control and treated areas using
Analysis o f Variance in GLM, using SYSTAT Version 10 (SPSS, Inc. 2000). In all cases a=0.05

2.2.2 Data Logger
A Campbell (Logan, UT) 2 IX micrologger was set up in plot 3 o f the control stand on
May 4, 2001, Julian Day (JD) 124 to monitor 8 temperature sensors. Temperature sensors 1-6 were
placed on three separate spruce trees on each tree’s terminal leader next to the stem on the north
side. Sensors 1 and 2 were placed on the leader o f a tree 29736 with shade from surrounding birch
trees. Sensor 3 and 4 were placed on a tree 29793 in the open receiving no shade at any time of the
day. Sensors 5 and 6 were placed on tree 29738 receiving shade at some parts of the day. Sensor 7
was placed 1.3 m above ground on the north side o f the stem o f the open tree 29793. Temperature
sensor 8 was placed at 1.3 m above ground on the north side o f the stem o f shaded tree 29736. The
data logger was programmed to record temperatures at 1 min intervals and to take the mean
temperature for each hour (Appendix 1 - Data logger programs). It also recorded the maximum and

21

minimum temperatures during each hour. Three quantum, LI90SB, light sensors (Campbell
Scientific, Inc. Edmonton, AB) placed on extension poles in close proximity to the three leaders
with temperature sensors, measured continuous light intensity as photosynthetically active radiation
(PAR) from which an hourly mean was taken. Quantum sensors were calibrated prior to
implementation in the field by Ministry o f Forests Research Branch in Victoria (Appendix I). Light
readings were taken at the same intervals as temperature readings. The micrologger collected data
continuously between May 5-September 10,2001 (JD 125-253).
Between June 2-7 (JD 153-158) data were lost due to equipment failure. The missing
temperature data was interpolated from data on the same days collected with the same model
logger at North Willow located approximately 50 km SW o f Sinclair Mills, at 650 m elevation. The
data for light were estimated based upon data for light collected for each sensor prior to and after
the equipment failure. Degree-days were calculated using data collected for temperature between
May 5- Sept 10 (JD 125-253); prior to oviposition and up to emergence o f adult weevils. The base
temperature used was 7.2 C as per the requirements originally described by McMullen (1976).
Based on findings from Sieben ei al. (1997), the formula to calculate degree-days was modified by
adding 1°C: E(((Tmax+Tmin)/2 + l)-7.2)/24. If a value <0 was obtained, it was set to zero before
summing each day in the month. Data for light were calculated as a mean for each day.

2.2.3 Leader dissections and parasite identification
In the summer o f 2000,37 attacked leaders, from outside the sample plots in the control
area, were clipped below the 1999 terminal and labelled according to whether the leader was from
a tree growing in the open, or in full or partial shade. In late August 2000, leaders were placed in
individual poly vinyl chloride (PVC) tubes for 1 month. After the adult weevils emerging from
each leader were counted, the leaders were dissected and counts were made o f un-emerged and

22

immature adults, as well as larvae of natural enemies, identified as either the predator L. cortics, or
as unknown hymenoptera parasitoids.
Spruce leaders were also clipped from outside the sample plots in both the treated and
control area before emergence o f weevils on August 17, 2001. At this time, 20 and 21 successfully
attacked leaders, 20 and 21 from the control and treated area respectively and 15 leaders from each
area with no visible sign o f weevil damage were excised. Adult weevil emergence was quantified
by the presence o f exit holes, assuming that one exit hole corresponded to one insect. Leaders from
both treatment areas were dissected and the number o f predators and parasites was counted and
identified as above.
Analyses o f variance for emergence o f adult weevils and number o f predators and parasites
were made to test for differences between the means for three levels o f shade in 2000 and between
sites in 2001 using a general linear model (GLM) in SYSTAT Version 10 (SPSS, Inc. 2000). In all
cases a=0.05.

2.2.4 Light measurements using Ceptometer
Using 2 AccuPAR (Decagon, Pullman WA) ceptometers, all spruce trees were sampled for
light received near the leader-tip o f each tree in 2001. Photsynthetically active radiation (PAR)
samples were taken, using manual and full-sensor mode to include sensors along the full length of
the probe (Anonymous 2001), between 1000 and 1400 on all sampling days. Two samples were
collected for each tree, on the south side at approximately mid-length of the terminal leader.
Samples were simultaneously taken using a second Ceptometer located in the open. Terminal
branches were reached using a 4.8 m orchard ladder. Samples for trees that were above 5.4 m and
could not be reached were taken at the maximum height possible. The first samples were taken on
9 and 10 May, 2001 before deciduous bud-break and the second set of samples were taken on 6 and
7 June, 2001 after all surrounding birch had completed bud-flush. The ratio o f light received by
each tree before and after bud-flush was calculated according to the open light sample taken. Hence

23

a tree that was in direct light without shade received a ratio o f 1, and shaded trees received a value
between 0 and 1 (Appendix II).

2.2.5 Light measurements using Plant Canopy analyzer - Leaf Area Index (LAI)
Light transmission was estimated using the plant canopy analyzer 2000 (LI-COR, Inc.
Lincoln, NB). Four samples, were taken in a selection o f the 5.64 m control plots on June 12 and
13,2001, and the mean o f all samples was taken. Above-canopy readings were made using a 4.8 m
orchard ladder. Below-canopy readings were made at 1.3 m. Readings were made in one sensor
operating mode, using one above canopy reading and four below canopy readings (Anonymous
1992). Samples were taken from a variety o f gaps and levels o f shade within each plot. Output is
given as a dimensionless figure, ratio m^ foilage/m^ground area (Appendix H).

2.2.6 Light measurements using portable spectroradiometer (Li 1800)
Sample measurements under varying canopy conditions were made in plot 2 and in the
open on June 4, 2000 using a portable spectroradiometer Li-1800 (LI-COR, Inc. Lincoln, NB) to
determine differences in light quality in different parts o f the stand. Measurements were made by
placing the equipment on a 1 m stand (Appendix II).

2.3 Results
Spruce stocking ranged from 1000 to 1600 sph, with a mean o f 1346 sph (± 49.6 SE) in the
treated area and from 800 to 1600 sph with a mean o f 1135 sph (±56.8 SE) in the control area
(Figures 2.2 & 2.3, Table 2.1).

24

I Birch ■ Spruce a Attacks 2000 □ Attacks 2001
3500

& 2500

# 2000
V 1500
i 1000

w

10

11

12

13

14

15

16

Figure 2.2 Number o f spruce and birch stems per ha in control (un-treated) and number of
individual attacks by weevils in 2000 and 2001 in sample plots 1-17. Trees attacked by weevils
were classified as either successful or unsuccessful.

I Birch ■ Spruce e Attacks 2000 □ Attacks 2001
3500
3000

»
ra 2000
®
1500
CL
V)

S 1000

w

500

10

11

12

13

14

15

Figure 2.3 Mean number of spruce and birch stems per ha in treated and number o f individual
attacks by weevils in 2000 and 2001 in sample plots 1-15. Trees attacked by weevils were
classified as either successful or unsuccessfiil.

25

Table 2.1 Mean (standard error) stems per ha for control and treated areas at

Control
Treated

Total

Paper birch

3465 (237.8)
1527(121.3)

2055(181.9)
180(1.6)

Interior
Spruce
1135 (56.8)
1346.6 (49.6)

Other^
276 (77.4)
NA

total of 47 stems, other than paper birch, were found in the control area
which included, in descending order o f total stems; Willow, Salix spp. (19),
black cottonwood, Populus balsamifera spp. trichocarpa (Torr. & A. Gray)
Brayshaw (16), Sitka alder, Alnus viridis spp. sinuata (Regal) Â. Love & D,
Love (7), trembling aspen, Populus tremuloides Michx., (3) and Douglas maple,
Acer glabrum Torr. var. douglasii (Hook.) Dippel (2).

There were few birch stems in the treated stand, which ranged from 0 to 1400 sph and a
mean of 180 (± 1.6 SE) sph in the control area (Figures 2.2 & 2.3, Table 2.1). Spruce diameters
increased significantly between years but were not significantly different between treatments
(Tables 2.2 & 2.3).

Table 2.2 Mean dbh cm o f spruce in control and treated stands in 1999,2000 and 2001
Treated

Control
1999

2000

2001

2000

2001

n

193

193

193

101

101

Mean

5.57

6.32

7.36

6.11

6.92

SE

0.15

0.14

0.16

0.22

0.26

26

Table 2.3 Repeated measures analysis in GLM, results for height, dbh and HDR (height to diameter
ratio) in response to fixed effects sources identified in a) between subjects and b) within subjects.
Source

df

M SHeight

p-value
Height

M Sdbh

p-value
dbh

M SHDR

p-value
HDR

Site

1

38.799

0.000

0.785

0.769

5584.367

0.000

Attack 2000

1

29.521

0.000

24.220

0.104

1249.225

0.077

Attack 2001

1

26.610

0.000

0.006

0.980

6261.157

0.000

Site * Attack 2000

1

0.881

0.458

16.355

0.181

559.112

0.236

Site * Attack 2001

1

8.990

0.018

2.770

0.581

1008.801

0.112

Error

282

1.592

396.834

9.093

b) Within subjects
df

MS
(Height)

p-value
(Height)

MS
(dbh)

p-value
(dbh)

MS
(HDR)

p-value
(HDR)

Time

1

35.794

0.000

60.407

0.000

254.674

0.005

Time * Site

1

0.010

0.748

0.483

0.075

131.018

0.046

Time* Attack 2000

1

.553

0.015

0.274

0.180

192.761

0.015

Time * Attack 2001

1

1.048

0.001

0.038

0.617

105.292

0.073

Time * Site* Attack 2000

1

.027

0.590

0.099

0.419

1.113

0.853

Time* Site* A ttack2001

1

0.202

0.139

0.295

0.164

95.476

0.088

Error

282

.092

Source

0.151

32.486

Heights were significantly greater in the control than in the treated area, and attacked
spruce trees were shorter than un-attacked spruce trees. In terms o f the model for height, everything
but site by attack in 2000 was significant (Table 2.3a & 2.4).

Table 2.4 Mean height o f spruce m in treated and control stanc s 1999-2001.
Treated
Control
2000
1999
2000
2001
n
193
193
193
101
Mean
3.42
3.96
4.57
3.13
SE
0.06
0.07
0.08
0.07

2001
101
3.72
0.09

27

There was an interaction between site and attack for the dependent variable (height) in
2001 (Table 2.3a). This occurred because attack rates in 2001 were much lower than in 2000.
When time is incorporated into the height model, to examine changes between years, height with
time was significant, because trees grew in height between measurement periods, but differences
between the control and treated stands were maintained between the years. There also was an
interaction between time and attack in 2000 and 2001 (Table 2.3b). This occurred because attack
rates differed between the two years at each site and trees that were attacked in 2000 were shorter
in 2001 .
Diameter, dbh, was not significantly different between sites. The only significant effect
occurred when time was incorporated into the model, because the trees grew in diameter between
the two years.
Height to diameter ratio (HDR) was significantly different between the control and treated
areas. HDR also differed significantly in trees attacked by weevils in 2001, with the control area
having a greater HDR than the treated (Table 2.3a). HDR changed with time and there were
interactions between time and site, and time and attack in 2000 (Table 2.3b). These interactions
appeared because the mean diameter was larger in the control than in the treated area. There was
little difference in diameter and height increments between treatments (Table 2.5).

Table 2.5 Mean diameter and height increment o f spruce in 2001 for treated and control stands
Diameter Increment (cm)

Height Increment (m)

Treated

Control

Treated

Control

n

101

193

101

193

Mean

0.93

1.02

0.63

0.60

SE

0.07

0.03

0.04

0.03

28

Birch (Table 2.6) were about 1.4 m taller and 2.5 cm smaller in diameter than spruce
(Tables 2.2, 2.4) in the control area. Other species did not contribute significantly to vertical
structure o f the stand and were not included.

Table 2.6 Mean, minimum and maximum height and dbh olr birch in 1999,2000 and 2001.
Height (m)

dbh (cm)

1999

2000

2001

1999

2000

2001

n

340

349

349

340

349

349

Min

1.50

2.00

2.80

1.00

1.20

1.50

Max

8.00

8.50

8.90

7.80

10.30

11.80

Mean

4.48

4.95

6.09

3.94

4.35

4.92

SE

0.05

0.05

0.05

0.07

0.07

0.08

Attack rates varied by treatment (Table 2.7) but did not vary by plot with each treatment
over the two-year study period (Figures 2.2 and 2.3).

Table 2.7. Mean yearly rates o f attack by weevil on spruce (percent o f total sample trees attacked
Control

Treated

1999

2000

2001

2000

2001

Percent Attack

16%

23%

9%

36%

27%

SE

0.27%

0.36%

0.26%

0.42%

0.34%

Over the 2-year study period levels of attack were a mean 16.1% in the control mid 31.1%
in the treated plots (Table 2.7). Rates o f attack for 1999 are only given for the control area as these
plots were measured early in the spring o f 2000 , before attack, or tree-growth had occurred while
plots in the treated area were not measured until later in the season.
Based upon Chi-square analysis percentage o f trees with poor and good form classes varied
significantly (Table 2.8) between each treatment area.

29

Table 2.8 Trees in control and treated area with good, moderate and poor form and
significant difference between each area by form class based on Chi-square
Form
Classes
Good (0)
Moderate (1)
P o o r(2)

% Trees
Treated
25
35
40

%
Trees Control
55
35
10

Chi-square

df

p-value

16.6
0.24
17.52

1
1
1

0.0002
0.9900
0.0002

Percentage of major defects was greater in the treated area compared to the control. Major defects
accounted for 10% of trees sampled in the control versus 41% o f trees in the treated area. Trees
with good form made up 55% o f trees sampled in the control area versus 25% o f trees in the treated
area. Moderate defects, damage caused by weevils on spruce above 2 m in height, were not
different between the two sites, with approximately 35% moderate defects for trees sampled in
each area.
From measurements taken using the ceptometer, there was a mean 23% reduction in light
intensity for the control stand after bud-break (Table 2.9).

Table 2.9 Mean light ratio (tree/open) received at leader level.

"

May 2001

June 2001

Mean o f 193 samples

0.94'

0.71

SE

0.01

0.02

____

because stems and branches caused shade

Mean leaf area index (LAI) for the control plots was 2.19, indicating a medium amount of
foliage coverage overall. The variation in measurements ranged from 0.8, little or no cover to 4.75,
indicating high levels o f deciduous cover at the location where the reading was taken (Figure 2.4).

30

C
45'
4■
35 ■
3.
<25-

2■
15
.

05-

1

It
1

1
1 ,1

il

1

rt -

*>

^

^

^

^

plot

Figure 2.4 Leaf area index (LAI) for control plots 1-6 and 9-12 taken on June 12 and 13, 2001.

In the open there were 697.6 degrees o f temperature accumulated, above the threshold
7.2°C during the sampling period. There were 657.9 and 654.0 degree-days accumulated above
7.2°C between May 5-September 20 (JD 125-263), on leaders o f the partially shaded and mostly
shaded trees respectively. Mean intensity of light at the leader decreased from the open-tree to the
mostly shaded tree and there was a greater difference between partial and mostly shaded trees in
contrast to degree-days. (Figure 2.5)

31

-shade

■open ■- » - -partial shade

S) 600

I 400
5 300

I I I I I U

I I I'T'I M

I n

I I! I

I

Julian Day

Figure 2.5 Photosynthetically active radiation (PAR) received in 2001 from May 10-Septermber 10
(JD 125- 253).

From the 41 successfully attacked leaders dissected in 2001, there was no significant
difference between sites for the number o f dipteran (predator) larvae or parasite larvae (Table
2 . 10 ).

Table 2.10 Comparison o f mean number o f diptera (predators) and

n
Mean
SE

Control
Diptera
20
23.7
6.7

Other
20
2.7
0.7

Treated
Diptera
21
21.8
5.4

Other
21
0.3
0.1

Mean number o f adult weevils emerging from the leader was greater in control compared to the
treated areas in 2001 (Table 2.11). There was no significant difference among the open, partially
shaded and fully shaded trees for weevil emergence or parasite number in 2000 (Table 2.12).

32

Table 2.11 Number o f adult weevils emerging from
Control
20
0.0
8.0
2.1
0.6

n
Min
Max
Mean
SE

Treated
21
0.0
9.0
0.9
0.5

Table 2.12 Mean number of live weevils, predators and parasites dissected from leaders
clipped in control plots in 2000 ; shade. partial shade and open in 2000 .
Shade

Partial Shade

Open (no shade)

Parasites
Adult
&
Weevils
Predators

Adult
Weevils

Parasites &
Predators

Adult
Weevils

n

12

12

12

12

13

13

Mean

4.4

11.9

5.47

9.5

7.2

12.1

SE

1.5

3.9

1.4

3.3

1.5

3.1

Parasites &
Predators

Spectral light quality changed under the canopy in comparison to the open, particularly in
the far-red and blue region (Figure 2.6).

33

-Openi ■■D--0pen2
1.00E+06
9.00E+05
8.00E+05
7.00E+05
6.00E+05
E 5.00E+05
* 4.00E+05
3.00E+05
2.00E+05
1.00E+05
O.OOE+00

o o o o o o o o o o o o o o o o o

o e o c D O i C M i n c o ^ ^ h - o c o o o c M i o c o
< 0 O ( 0 P 5 ^ ^ ^ l 0 l 0 l 0 < 0 < 0 < 0 t 0 h ' N ' f ^

Wavelength

a) Open
-Shade!

-Shade2

1.00E+05
9.00E+04
8.00E+04
7.00E+04

?■

6.00E+04

E 5.00E+04

^ 4.00E+04
3.00E+04
2.00E+04
1.00E+04
O.OOE+00
o
O

o o o o o o o o o o o o o o o o

CO

CD O)

CM

LO 00

^^r^oeo<oo)Csjmoo

o o o o o o o o o o
■«“

^ h - O C O < D O ) C M L O C O

Wavelength (nm)

(b) Shade
Figure 2.6 Light transm ission in W/m^’ by w avelength in plot 4, for trees in the open (a) and in
shade (b) on June 1, 2000; betw een 0956-1030.

34

2.4 Discussion
2.4.1 Growth of Spruce
In contrast to the contention that an overstorey of angiosperm trees reduces growth in both
height and diameter o f conifers (Logan, 1969; Stewart et al. 1984; Leiffers and Stadt 1994; Oliver
and Larson 1996 page 75; Wright et al. 1998), the presence o f an average 2055 sph of birch, up to a
maximum 3500 sph, in the control area at Sinclair Mills did not appear to reduce growth of spruce
in either height or diameter. Taylor et al. (1996) noted a trade off between overstorey shade in a
primarily aspen, Populus tremuloides Michx., canopy and height growth o f interior spruce. The
mean diameter increment o f the spruce was not different between the control and herbicide-treated
stands (Table 2.2), and the lower height o f spruce in the treated areas (Table 2.4) was likely due to
attacks by weevils, because height increment did not vary between areas.
Shade generally causes an etiolated effect in trees (Logan 1969). They grow taller with a
decreased diameter because carbon is first allocated to height growth and then to diameter growth
in limiting situations (Gordon and Larson 1968; Rangnekar and Forward 1973). In my study, the
23% lower light level in the control than in the treated area, may not be enough to etiolate 10-12
year-old interior spruces. Logan (1969), Leiffers and Stadt (1994) and Wright et al. (1998), found
that white spruce seedlings growing under 50% and full sunlight achieved similar height growth. It
is generally accepted that the best diameter growth in spruce occurs in full sunlight (Leiffers and
Stadt 1994; Wright et al. 1998). However, Eis (1967) suggests a diameter growth threshold o f 60%
full sunlight for white spruce. The hypotheses that growth o f white spruce >10 years old is optimal
under full sunlight (Logan 1969; Eis 1970) is supported by smaller height and diameter of white
spruce growing under a trembling aspen canopy than in the open (Johnson 1986; Yang 1989).
My results suggest that the growth o f interior spruce under a paper birch canopy is very
different from that under a trembling aspen canopy. This difference may be due to a variety of
factors. Silhouettes o f aspen and birch are different, with aspen having a greater crown area than
birch (Farrar 1995). The estimated site index, SI50 28m (estimated height o f trees, 28 m at 50

35

years), using the spruce site index equation (Nigh and Love 2000) is high compared to a lower site
indices in found in studies with an aspen canopy (Taylor and Cozens 1994). Benefits from the
presence o f birch may also be derived from ectomycorrhizal fungi that serve as a nutrient gathering
interface in the soil (Smith and Read 1997). Comeau (1996) reported increases in yield o f mixed
stands with a birch component compared to yields in pure conifer stands. Simard et al. (1997)
showed a mutualistic association with mycorrhizae, between paper birch and Douglas-fir. Simard
and Hannam (2000) reported that growth o f 8-year-old interior spruce in the Interior Cedar
Hemlock (ICH) subzone, was not constrained by competition with paper birch <4000 sph. Because
paper birch, at its present density on the Sinclair Mills site, appears to significantly aid spruce
growth and development and increase total site yields, treatment with herbicide for conifer-release
at this site does not appear to be justified.

2.4.2 Attack on Spruce by Weevils
The most reasonable explanation for lower attack by weevils in the treated than the control
area (Table 2.7) is that population o f weevils in the control area is lower in comparison to the
treated area. Although no difference was found in adult insects emerging from individual leaders,
there were many more spruce trees attacked by weevils in both 2000 and 2001 in the treated site
than in the control. However, taking into account 1135 sph at 16.1% attack rate per year and 2.1
weevils emerged per leader in the control area, and 1346 sph, at 31.1% attack rate and 0.91
emergent weevils per leader in the treated area (Table 2.1, 2.7, 2.11), there would be 384 and 380
emergent weevils/ha/yr in control and treated areas respectively. The question that must therefore
be asked is what determines the difference in attack success between the two areas?
The sample tree that was directly in the open received 697.6 degree-days above 7.2“C, or
89% of the required 785 degree-days (McMullen 1976; McIntosh 1997) between May 5Septermber 10 (JD 125-253). The shaded trees received approximately 41 degree-days less than the
open tree, or about 83% o f the degree-day threshold for life cycle completion, than the open tree.

36

The temperature requirements were not met at Sinclair Mills, even though the revised formula by
Sieben et al. (1997) was used. Insect emergence was still observed in both the control and the
treated areas, but may have been higher if degree-day temperatures were greater. Error in field
equipment and sensor-placement would have factored into the final heat-sums. Elements such as
wind velocity and humidity, which were not measured, may have also affected the readings of the
temperature sensors. However, temperature, may have played a part in reducing brood
development in 2001 as the rates of attack were significantly lower in the control (9%), compared
to the treated area (27%). Rates o f attack in the treated area were very high which leads to
speculation that physical factors, other than temperature, need to be considered in the role of
weevils attacking spruce.
It was observed that weevils continued to feed, mate and oviposit well after deciduous leaf
development had occurred in the control area. It was also observed, in both years, that weevils
emerged and started feeding and mating sooner in the treated than in the control area. These
differences may have more to do with the soil temperature than a direct result o f differences in light
because exposed soil tends to warm sooner than shaded soil (Stathers and Spittlehouse 1990). Sites
where weevils overwinter would therefore warm earlier in open compared to sites located in the
shaded stands. The exposure to the open areas also allows for earlier snow melt, thus making water
available to the trees sooner, thereby allowing for earlier development. In this study, spruce trees in
the treated area started bud-break one to two weeks before those in the control area. According to
Hulme (1995) spruce that flush later are more susceptible to attacks by weevil than those that flush
earlier, which may explain the greater emergence o f weevils from attacks that did occur in the
control area.
The quality o f light was different when weevils were still feeding and laying eggs (Figure
2.6). Portions o f the spectrum diminished under shade o f the birch, may affect the ability o f weevils
see the terminal, particularly because the near infrared spectrum became one of the more prominent
wavelengths under the birch canopy.

37

The lack of any difference in number o f parasites and predators dissected from the clipped
leaders between the shaded and open leaders was unexpected. McLean (1989) found more parasites
in the open than on Sitka spruce growing under red alder. Previous studies (Stevenson 1967; Nealis
1998) have speculated that predators and parasites may be a significant factor in controlling weevil
populations. My results support this hypothesis in part because numbers o f emerged weevils were
lower (Table 2.11). The greater number o f parasites and predators in the 2000 leaders than in the
2001 leaders may be due to temperature variation between 2000 and 2001 .

The greater percentage o f trees with very poor form in the treated than control stands can
be attributed to the many years of successive attack by weevils. Although the estimates o f historical
attack, 75% and 80% for control and treated stands respectively, do not vary greatly between sites
the exact number o f times a tree has been attacked cannot be assessed without destructive
sampling. Trees with minor damage did not vary significantly between stands. Because both the
control and treated areas were relatively similar before the 1996 treatment with herbicide,
apparently it took only 4-5 years for impact levels o f attack in the treated and control areas to
diverge.
Tree vigour, or growth appeared to have an impact on levels o f attack only in 2001 (Table
2.3) as HDR did not significantly affect levels of attack in 2000. Diameter increment was not
significantly different between the control and treated areas. Therefore, the effects o f growth rate
on attack, are only speculative. King et al. (1997) noted that the fastest growing trees o f interior
spruce were attacked more frequently than slow growing trees. However, faster growth has also
been linked with greater resistance to attack by white pine weevil (Kiss and Yanchuck 1991). At
Sinclair Mills, attack may be affected by rate of spruce-growth. The reason that HDR was only
significantly related to attack in 2001 is unknown. Timing o f spruce bud-break, or some other
factor, may also be key in determining whether weevils successfully attack the spruce. Because the
spruce trees appear to break bud later in the control than in the treated area, yet manage to have an
equal growth increment, may mean that the spruce in the control are growing at a faster rate

38

through the season. The less likely alternative is that spruce in the control plots maintain their
growth later into the season than the spruce in the treated area. This latter explanation is unlikely as
conifers are cued by photoperiod to complete growth (Dormling 1989) and the spruce seed source
was the same for both the control and treated areas. The former explanation could only hold if the
growth environments were significantly different, which they were with respect to light and
temperature.

2.5 Conclusions
Interior spruce tree form and mean tree height were significantly better and rates o f attack
by weevils were significantly less in the control area. Birch densities in the control ranged from
700 to 3500 sph and mean total densities o f spruce and birch were 3465 sph. These findings have
important ramifications for forest policy in British Columbia. The control area does not meet freegrowing criteria for competition o f deciduous species and the treated area was not free-growing
due to levels o f attack by weevil. Interspecific competition at the observed densities did not reduce
crop tree growth at 13 years, but appears to have a negative impact on attack by white pine weevil.
Further studies are necessary to determine the specific mechanisms which result in reduced attack
by weevil under paper birch or other species that form deciduous canopies. Studies like this will
need to be followed in the long-term to determine the if there will be an impact on volume of
spruce at the time of harvest. More importantly, replicated experiments need to be installed, or
replicates already established need to be measured.

39

CHAPTER 3

Open pollinated interior spruce families and resistance to white pine weevil under varying degrees
of shade

3.1 Introduction
The Prince George Forest Region has approximately 300,000 hectares o f interior spruce,
plantations, >34,000 ha o f which are at risk to attack by the white pine weevil (Taylor et al. 1996).
Employing a combination o f silvicultural tactics, which include the planting o f spruce stock with
known resistance traits, should mitigate damage caused by the weevil (Alfaro et al. 1995).
The objectives o f this investigation were to determine 1) if resistance to white pine weevil
could be shown at a young age in progeny trees in families with known weevil resistance, 2 ) if
varying light levels affected feeding and oviposition behaviour o f white pine weevils and if light
levels affected growth o f spruce, and 3) if there were interactions among spruce family, light level,
and attack by weevil. I hypothesized that trees subjected to artificial shade would be attacked less
than open-grown trees, and eggs would be deposited in a more dispersed manner along the
terminal. It was also believed that trees from families with a high resistance-ranking would be
attacked less by weevils, regardless o f shade or light treatment.

3.2 Methodology
Seeds from trees o f 40 open pollinated families o f interior spruce, Vernon Seed Orchard
#214, were collected by family in 1996. All o f the families were ranked according to growth and
resistance to P. strobi. Seeds were sown and grown in 1997 at the JD Little Forestry Centre, near
Prince George. Seedlings were spring planted, from 41 SB 1+0 stock, in two trials near Prince
George in 1998. At Pass Lake, 90 Km northeast o f Prince George (Latitude: 54° 15' N, Longitude:
121°42' W -1000 m in elevation) in the SBSvk 01, the layout included 160 squares with 25

40

seedlings each planted 2.5m apart. Each family was replicated four times. Five o f the 40 families
planted at this location were selected for testing in 1998, based upon their ranking for weevil
resistance by the Ministry o f Forests (Table 3.1).

Table 3.1 Selected families showing original white pine weevil resistance ranking, breeding value.

Family

Weevil
Resistance
Ranking'

Breeding
Value^

Elevation
(m)

Latitude

Longitude

16
21
27
139
140

4 (high)
6 (high)
38 (low)
2 (high)
31 (low)

18.7
19.8
16.1
25.4
23.9

685
732
763
899
777

53“ 56'
53“ 54'
53“ 53'
53“ 47'
52“ 47'

122“ 06'
122“ 02 '

1 T,

122“ 18'

122“ 25'
122“ 01 '

No. trees successfully
Attacked in 2000
5
3
5
6
4

_

^ Expected percentage increase in volume at rotation

Two shade treatment levels (65 and 28% full light, 1 and 2 layers o f shade cloth,
corresponding to light and heavy shade respectively) were set up over the 20 randomly selected
seedlings (10 per treatment) in each family and another 10 seedlings per family were randomly
selected as open-grown controls exposed to full light. Light and heavy shade treatments were set up
using neutral density greenhouse shade cloth, set at 45“ to the south, over posts set to the east and
west o f each tree. East and west aspects were also appropriately shaded. Heights and leader
diameters o f all seedlings were taken for 1999 growth on May 12,2000. Trees were again
measured for height and diameter at the end o f August 2000, and only for height in August 2001.
Five weevils collected from a nearby naturally infested stand were placed on 15 (5 per light
treatment) o f the 30 randomly selected spruce-seedlings in each family, on May 17, 2000, before
they broke bud. Oviposition punctures, determined by the black fecal plugs, was categorized as;
absent, dispersed along the stem of last year’s terminal growth or aggregated within 3 cm of the

41

terminal bud o f the 1999 leader. Punctures were counted weekly for four weeks and final
categories were assigned on June 19,2000.
Temperature was averaged hourly using a Campbell (Logan, UT) 21X micrologger, and
the daily treatment mean temperature above 7.2°C was determined from May 15-September 5 (JD
135-248) using the formula: Z(((Tmax+Tmin)/2 + l)-7.2)/24. Light quality was sampled under
each light regime on June 4,2000 using a portable spectroradiometer Li-1800 (LI-COR, Inc.
Lincoln, NB). Successful attack, denoted when a tree’s terminal leader was girdled and dead or
dying from attack by weevil, was determined in late August 2000.

3.2.1 Analyses
Factorial repeated measures ANOVAs using SYSTAT Version 10 (SPSS, Inc. 2000) were
done on leader growth and diameter. The independent variables were family, shade treatment,
weevil seeding and their interactions. Kruskal-Wallis analyses were also done for attack success
and oviposition density, on trees that had been seeded with weevils. Chi-square analyses were used
to determine difference in dispersal of oviposition punctures for each level of shade. In all cases
a=0.05.

3.3 Results
There was no significant difference in height or height growth among the five families (Tables
3.2, 3.3a).

42

Table 3.2 Mean height (cm ±SE) of 30 spruce trees from each o f five families at Pass Lake in
1999,2000 and 2001.
Mean Height (cm ±SE) by year
Family and Resistance Level
2000
Treatment
1999
2001
Control
45.5(1.5)
57.9 (2.3)
70.1 (3.4)
16 (high)
Weevil'
56.7 (3.4)
45.3 (1.9)
64.9 (5.6)
Control
44.1 (0.9)
58.7(1.0)
70.1 (2.1)
21 (high)
Weevil'
45.4(1.6)
59.5(1.6)
68.0 (3.4)
27 (low)
Control
44.2(1.0)
56.3(1.6)
68.1 (2 .8 )
Weevil'
45.0(1.5)
52.8 (2.3)
58.0 (2.8)
139 (high)
Control
43.1 (1.2)
56.6(1.7)
66.6 (3.2)
Weevil'
43.2(1.6)
55.4 (2.7)
59.6 (5.6)
43.9(1.2)
55.9(1.8)
140 (low)
Control
68.5 (2.9)
Weevil'
42.6 (2.0)
54.3 (2.4)
61.8 (3.1)
Trees in weevil treatment seeded with weevils before bud-flush in 2000.

Table 3.3. Repeated measures analysis o f variance results for height in 1999, 2000 and 2001, in
response to resistance, shade treatment and weevil seeded trees (fixed effects) sources identified
in a) between subjects and b) within subjects.
Source
Resistance
Shade
Weevil
Resistance*Shade
Resistance*Weevil
Shade*Weevil
Resistance*Shade*Weevil
Error

SS
260.88
87.90
1885.88
2349.79
662.75
158.88
2646.74
21199.29

b) Within Subjects
Source
SS
Time
40700.56
194.61
Time*Resistance
Time*Shade
154.41
Time*Weevil
2252.29
Time*Resistance*Shade
1644.38
635.71
Time*Resistance*Weevil
Time*Shade*Weevil
46.09
Time*Resistance*Shade*Weevil 1175.51
Error
13354.66

df
4
2
1
8
4
2
8
109

MS
65.22
43.95
1885.88
293.72
165.69
79.44
330.84
194.49

F
0.335
0.226
9.697
1.510
0.852
0.408
1.701

p-value
0.854
0.798
0.002
0.162
0.495
0.666
0.106

df
2
8
4
2
16
8
4
16
218

MS
20350.28
24.336
38.60
1126.15
102.77
79.46
11.52
73.47
61.26

F
332.196
0.397
0.630
18.383
1.678
1.297
0.188
1.199

p-value
0.000
0.921
0.641
0.000
0.052
0.246
0.944
0.270

43

Weevil-seeded trees were significantly shorter than control trees (Table 3.3a). Withinsubject tests for height, using repeated measurements in ANOVA, show a significant difference
with time, because trees grew between measurement periods (Table 3.3b). Repeated measurements
also revealed that there was an interaction between time and trees that had been weevil-seeded in
between subject tests (Table 3.3b). This occurred because the trees that were attacked in 2000 were
shorter, resulting in the interaction between time and seeding with weevils.
There was a significant difference in leader basal diameter among families, in both 1999
and 2000 (Table 3.4 and 3.5).

Table 3.4 Analysis o f variance for girth (leader basal diameter) in 1999 between Resistance
Source
Resistance
Shade
Weevil
Resistance*Shade
Resistance*Weevil
Shade*Weevil
Resistance *Shade*Weevil
Error

Sum-ofSquares
9.387
1.002
0.068
3.217
1.728
0.677
1.687
92.419

df

Mean-Square

F-ratio

p-value

4
2
1
8
4
2
8
120

2.347
0.501
0.068
0.402
0.432
0.338
0.211
0.770

3.047
0.651
0.088
0.522
0.561
0.439
0.274

0.020
0.523
0.767
0.838
0.691
0.645
0.973

3.5 Analysis of variance for leader basal diameter in 2000 between Resistance, shade treatment
and weevil seeded trees and their interactions.

Resistance
Shade
Weevil
Resistance *Shade
Resistance *Weevil
Shade*Weevil
Resistance *Shade* Weevil
Error

Sum-of-Squares

df

Mean-Square

F-ratio

p-value

10.492
1.837
2.481
5.703
4.879
0.729
2.503
75.718

4
2
1
8
4
2
8
105

2.623
0.918
2.481
0.713
1.220
0.365
0.313
0.721

3.637
1.274
3.440
0.988
1.691
0.506
0.434

0.008
0.284
0.066
0.449
0.157
0.605
0.898

44

All other variables were not significant and there were no interactions between them.
Repeated measures were not used for girth as measurements were taken at different points o f the
leader in each year. Family 139 had the greatest leader diameter in 1999 and 2000 (Table 3.6).

Table 3.6 Mean leader diameter (mm ±SE) in 1999 and 2000 for 30 spruce trees from each
Family and Resistance
16 (high)
21 (high)

27 (low)
139 (high)
140 (low)

Mean Leader Basal diameter (mm ±SE)
1999
2000
4.0 (0.1)
3.0 (0.1)
4.3 (0.1)
2.6 ( 0 . 1)
4.5 (0.2)
3.0 (0.2)
4.7 (0.2)
3.3 (0.2)
4.6 (0.2)
3.2 (0.2)

There were 832.0, degree-days above 7.2°C for the open grown trees, and 789.1 and 707.0
degree-days under light and heavy shade respectively, approximately 94.8% and 84.9% o f the heat
received in the open. Differences in light intensity under each treatment, throughout the season are
seen in Figure 3.1.

-o p en

O

"light ■

-h eav y |

Julian Day

Figure 3.1 Mean light intensity (PAR) for each shade treatment (light and heavy) and in the open at
Pass Lake for the May-July 2000 period.

45

Light quality was not changed under each shade treatment indicating that the shade cloth
was neutral density (Figure 3.2).
Op 0 n • • ♦ ■ • Light — A— Heavy

7.00E+06
6.00E+05
J

5.00E+05

3.00E+05

f
Figure 3.2 Energy o f light by wavelength in the open and under light and heavy shad, June 1,
2000,11:00 at Pass Lake.

In 2000, 23 successful attacks were distributed almost uniformly among the five families
(Table 3.1). There were no differences in the number o f successful attacks in the heavy shade
compared to the light shade or open treatments: 6 versm 9 and 8 attacks respectively. There was a
significant difference am ong the three light treatm ents for oviposition category (Table 3.7).

Table 3.7 Kruskal-Wallis test statistic and significance for non-parametric tests between
number o f successful attacks and resistance, shade and oviposition pattern (category) and
resistance and shade treatment.
Kruskal-Wallis Test
Grouping Variable
Dependent Variable
p-value
statistic
Attack Success
Resistance
1.103
0.894
Attack Success
Shade
0.865
0.649
Oviposition category
Resistance
3.482
0.481
Oviposition category
Shade
6.173
0.046

46

Trees under heavy shade had the largest number of trees with no oviposition and the lowest
level of aggregated oviposition punctures. In contrast, the greatest number of trees with aggregated
oviposition punctures were growing in the open (Table 3.8).

Table 3.8 Number o f trees in each shade level per oviposition category, showing significant
Number of trees per Shade Level
Oviposition
Category

Open

Light

Heavy

ChiSquare

df

Pvalue

Absent

12

9

18

12.880

2

0.002

Dispersed

4

12

5

5.199

2

0.055

Aggregated

9

4

2

7.119

2

0.037

47

3.4 Discussion
Early performance results from this trial were not consistent with the original breeding
value and weevil rankings. Family 27, which had the lowest resistance-ranking and breeding value,
had relatively large diameter-growth. Family 16, which was ranked high ranking for resistance to
weevils had the lowest overall leader-growth. These findings may be due to several factors. All
families were originally tested under well-maintained research conditions unlike the operational
conditions at Pass Lake. All families except 139 were from low and mid elevation sites and
movement to an elevation o f 1000m at Pass Lake exceeded the 200 m maximum change
recommended for interior spruce (Anonymous 1995). A nursery-effect, influencing the health and
vigour of the seedlings after leaving the nursery, may have been present in the field, three years
after planting, resulting in trees in families with low breeding values to perform better than
expected.
Resistance by plants to insect attack can result from a combination o f many traits. Some of
the factors that influence these traits are related to growth rate (Kiss et al. 1994; King et al. 1997).
The trees in this study may not be old, or large, enough to yet exhibit some o f these resistance
traits. Previous rankings for resistance were based on older trees performing well in areas where
attack by weevils occurred endemically. Presence o f white pine weevils reduced leader basal
diameter and leader growth in some families even though the insect did not cause visible damage
(Table 3.4 & 3.5). However, this effect was not significant in all families. Reduction in girth may
be due to adult insects feeding on the stem or by larvae, having fed inside the stem but not
developing fully after oviposition. Predators such wasps and flies, are known to kill weevil-larvae
(Hulme and Harris, 1988) and may have contributed to the lack of successful attack by weevils.
Past studies have shown that shade reduces the diameter growth o f the leader making it an
unfavourable host for the weevil (Sullivan 1961). Diameter growth in this study was not
significantly affected by light level but instead by family. The trees from this study may have been
too small to have an effect on whether or not weevils choose them as hosts. However, in a study by

48

Kiss et al. (1994), it was shown that weevils attacked interior spruce regardless of leader length or
diameter, and genetic resistance was the greatest determinant of attacked seedlings. In my study,
weevil feeding was observed on most of the weevil-seeded trees even when no oviposition
punctures were observed.
Density o f oviposition punctures differed significantly by light treatment levels, although
attack success did not. Successful attack is ultimately the most important criterion in determining
the effectiveness o f shade as a control measure. However, this still may have implications for
planting spruce under deciduous cover, if future studies show that natural shade reduces success of
attack and growth of spruce is not reduced.
The level o f shade did not affect the growth o f spruce. This is not surprising as previous
results (Logan 1969) have shown that white spruce planted under 50% light intensity can reach
optimal height-growth. The trees growing in the open, or full light condition, had the largest
number of trees with aggregated oviposition. This is significant because the insect must lay eggs
that are dense enough for hatching larvae to find one another to form a communal feeding ring
(Silver 1968). If eggs are laid dispersed along the stem, the larvae become drowned in the trees'
resin and the leader continues to grow (Silver 1968). Therefore, the light shade treatment (65% full
light) should not reduce spruce height growth but significantly reduce aggregated weevil
oviposition, while the heavy shade treatment (28% full light) will meet reduced attack by weevil
objectives but reduce spruce growth based upon Logan's (1969) observations.
McMullen (1976) found that 785 growing degree-days above 7.2°C were needed in order
for weevils to develop in the leaders of white spruce. Temperature data collected for the 2000
season revealed that there was sufficient heat accumulation during the season, under the open and
light shade conditions but not under heavy shade. Successful attacks were observed on 23 of the
weevil-seeded trees, which is considered to be a high level of attack (Wallace and Sullivan 1985).

49

The trees in this study may be too young to determine whether resistance to weevil is
significantly different among the families selected for this study. The trees and families may begin
to exhibit more resistance traits as they grow older and become acclimatized to the Pass Lake site.

3.5 Conclusions
The shade treatments caused the weevils to oviposit in a more dispersed pattern. However,
this result did not appear to affect overall development o f weevils in the light shade treatment,
which had the greatest number o f successful attacks. Lowered light intensity, or greater shade level
also did not reduce growth o f the selected spruce families. Further studies need to be undertaken to
determine the role o f light on oviposition behaviour o f the white pine weevil, growth o f spruce, and
forest management implications.

50

CHAPTER 4

Environmental factors affecting behaviour o f weevils on interior spruce clones produced by
somatic embryogenesis

4.1 Introduction
Open stands o f conifers are more vulnerable to attack by white pine weevil because light
and temperature are increased in the open, which affects behaviour of adult insects (Sullivan 1959,
1960) and development o f the brood (McMullen 1976). Previous studies (Cozens 1983; McLean
1994; Taylor et al. 1996) have shown that a deciduous overstorey and side-shade reduces attack by
weevils on spruce. Sullivan (1961) noted that in open growing stands o f white pine, weevils
confined their attack to the leader and moved down the stem during the season until the distribution
of punctures was relatively even throughout the length o f the leader. The tendency was towards a
greater proportion o f oviposition punctures near the tip o f the leader. However, on trees that were
shaded, the distribution and frequency o f oviposition punctures differed (Sullivan 1961). This is
important because a dispersed pattern o f oviposition lessens the chances o f brood success as the
likelihood o f individual larvae surviving to adulthood is lessened.
This study follows from investigations undertaken in the summer o f 2000 on open
pollinated spruce seedlings (Chapter 3), in which it was observed that oviposition punctures made
by weevils placed on interior spruce under artificial shade were lower, and less aggregated on the
stem than those on open-grown trees. Using clones produced by Somatic embryogenesis (SE)
(Webster et al. 1990) allows an investigator to eliminate population genetic variance in
experimental procedures. By utilizing many trees o f one clone, differences in weevil behaviour can
be attributed to environmental effects such as overstorey shade.
The objectives o f this study were to determine 1) if reduced light has an effect on
behaviour o f weevils, 2) if clones from parents previously ranked for resistance to weevils sustain

51

levels of attack that reflect fheir ranking, and 3) if bud development within clones is related to
resistance to weevils. Based on the results in Chapter 3 ,1 hypothesized that weevils placed on trees
under shade would lay eggs in a dispersed pattern further down the stem than on trees in full light.
Because o f the more dispersed and less aggregated pattern o f oviposition, weevil-larva might not
be able to form feeding rings, thus fewer leaders would be killed and there would be fewer adult
weevils emerging from each infested terminal.

4.2 Methodology
4.2.1 North Willow
Two SE clones o f interior spruce were observed for resistance to attack by P. strobi. The
selected clones were located in two o f several trials planted in 1996 in the Sub Boreal Spruce
(SBS) mkl 03, 05, 07 (moist cool, subhygric), located at North Willow, approximately 50 km east
o f Prince George (Latitude: 53°57' N, Longitude: 122° 10' W). The trees were planted in at 2.4 m
spacing in blocks of 0.20 ha (clone 1-1026) and 0.15 ha (clone 107-1930). The source o f clone 1071930 originated from parents o f high growth and weevil resistance rankings, while clone 1-1026
originated from parents o f moderate growth and weevil resistance rankings (Hawkins 1998) (Table
4.1).

Table 4.1 Growth and resistance ranking (Hawkins 1998) for SE clones from original 173 parents'
ranked.
Mother - Weevil
Father - Weevil
Mother - Growth Father - Growth
SE Clone
Resistance
Resistance
1-1026

4

78

20

97

107-1930

1

5

10

2

U284

60

36

83

15

J974

4

102

20

130

U185

60

36

83

15

-1..— -'"T " "!" ;" :

52

In 2001, 30 vigorous and healthy trees were randomly selected from each clonal block and
measured for height and leader basal diameter and grouped into triplets based upon total tree height
and 2000 leader growth. Each seedling in a triplet, was then randomly assigned one o f three light
treatments; no shade, light shade or heavy shade. Shade treatments were applied between April 30
and May 3, 2001 using 2.4 m lengths of neutral density greenhouse shade cloth (65% o f light
transmittance). Two, 2.4 m x 0.05 m x 0.05 m posts were driven 0.16 m into the ground 0.75 m to
the east and west o f each seedling. The cloth was affixed on both posts with staples, and secured to
the ground with wire and metal stakes, so that 1 m o f the cloth was directed to the north o f the
seedling and 1.4m was directed to the south o f the seedling in a 45° angle. One or two layers of
cloth was used to create either light shade (65% full sunlight) or heavy shade (28% full sunlight).
The cloth was porous enough to allow moisture and wind through. Weevils were collected in a
heavily infested stand approximately 100 km North east o f Prince George on May 14 and 15th,
2001.Trees in half o f the triplets in each clone and shade treatment were seeded with five weevils
per tree on 15 May 2001.
Between May 12-August 29,2001 (JD 132-241) a Campbell (Logan, Utah, U.S.A.) 21X
data logger with three quantum sensors (Campbell Scientific, Inc. Edmonton, AB) and eight
temperature sensors recorded light and temperature continuously on trees in the block containing
SE clone 107-1930. A quantum sensor was placed at leader height affixed on a separate post beside
the seedlings for each o f the three light treatments. Two copper-constantin thermocouple sensors
were placed on the north side o f the leader just under the leader bud produced in 2000. One
thermocouple was placed in the soil and the final sensor was placed in the open on the leader o f a
tree away from the bark, to measure air temperature. Daily treatment mean temperature above
7.2°C was determined using the formula; Z(((Tmax+Tmin)/2 + l)-7.2)/24. Between July 18-August
3 data lost due to equipment malfunction were interpolated based upon data from the same model
data logger placed at Sinclair Mills. Lost light data were interpolated based upon data collected
before and after the equipment failure (see Appendix 1).

53

4.2.2 U pper F raser
The second study site was located at Upper Fraser, approximately 80 km North East of
Prince George (Latitude: 54°03' N, Longitude: 121°42' W) in the Sub Boreal Spruce Zone, wet,
cool subvariant (SBSwkl 01). Trees at this location were planted at 2.4 m spacing in 1995 in 0.11
ha blocks. Twenty healthy and vigorous trees from each o f clone U284 and J974 were randomly
selected and measured for height and leader basal diameter. Clone U-284 originated from parents
o f moderate growth and resistance to weevils, and clone J974 originated from parents o f moderate
growth and low resistance ranking (Table 4.1). Trees within each clone were paired according to
similar height and 2000 leader growth. Trees in half o f the pairs were seeded in 2001 on 17 May,
2001 with weevils collected as above. No shade treatment was applied.

4.2.3 Assessments
The following data were collected weekly between May 14 and July 17 between 1000 and 1400 at
both sites:
1. weevil behaviour: absent, feeding, mating or egg laying (oviposition sites present),
2. number o f oviposition punctures on each leader as described by Wallace and Sullivan (1985),
3. distance o f the furthest oviposition puncture from the top o f the apical bud,
4. phenology o f spruce bud burst o f the leader and one lateral on the first whorl, using the
classiAcation adapted from Alfaro et al. (2000): (1) shiny conical - buds slightly conical with
scales; (2) shiny/swollen - buds similar to the first stage but more swollen; (3) light brown/swollen
- buds considerably swollen and lighter in colour than second stage; (4) columnar - shoots starting
to elongate and bud scales are opaque so that green needles are visible; (5) split - shoot elongating
and bud cap split; (6) brush - bud cap usually no longer present, needles appear to originate from
one point; (7) feather - needle bases separate (8) growing shoot - needles widely separated out
from expanding shoot.

54

All trees were measured for height and basal leader diameter on August 27, 2001. At this
time, trees were classified as successfully attacked, based on leader-death, or not successfully
attacked if the 2001 leader survived the weevil- seeding treatment. Leaders from weevil-seeded
trees were removed from the tree beyond the point o f initial 1999-year growth on August 29, 2001.
Emergence holes were counted and each leader was dissected. Predators, parasitoids and weevil
pupae were counted.

4.2.4 Upper Fraser 8 - block survey
At Upper Fraser, another clone, U185, with the same growth and weevil ranking as U284
(Table 4.1) was observed for growth and resistance to weevil. These trees were planted in eight
blocks in 1995 along with seed orchard seed lot 6863 (Central Plateau) in the ratios U185:6838,
100:0, 67:33, 33:67 and 0:100, with four blocks using Peltons Nurseiy (PL) and four using stock
form Green Timbers Nursery (GT). In early May 2001, 50 trees in each were systematically
selected and tagged, and then measured for height, history o f attack by weevil and attack in 2000.
The blocks were re-visited in August 2001 to measure height and count current attack by weevils.

4.2.5 Statistical Analyses
All growth data were analyzed using analysis o f variance, ANOVA, in SYSTAT Version
10 (SPSS, Inc. 2000). Categorical data were analyzed using Kruskal-Wallis nonparametric analysis
to determine differences in shade treatments. The Kruskal-Wallis test automatically converts to the
Mann-Whitney test, the non-parametric equivalent o f the two-sample t-test (SPSS, Inc., 2000),
when only two categories are present and was therefore used to determine differences between two
shade levels or differences between clones in bud-flush. In all cases a=0.05.

55

4.3 Results
4.3.1 North Willow
There was no significant difference in height between clones and no interactions for all
trees, but a significant difference in height between clones occurred for trees that had not been
successfully attacked by the white pine weevil (Table 4.2a).

Table 4.2 Repeated measures analysis o f variance results for height in 2000 and 2001, for clone,
shade treatment and weevil seeded trees and their interactions at North Willow, sources identified
in a) between subjects and b) within subjects.
df

p-value
All
trees
0.092
0.444
0.304

df

Clone
Shade
Weevil

1
2
1

M Sheight All
Trees
837.766
233.593
304.552

Clone*Shade
Clone* Weevil
Shade* Weevil
Clone*Shade* Weevil
Error

2
1
2
2
48

10.679
40.745
186.332
785.951
282.512

0.963
0.706
0.522
0.072

2
1
2
2
41

0.219
51.621
127.949
226.732
254.688

0.999
0.655
0.609
0.418

b) Within Subjects
Source

df

1
1
2
1
2
1
2
2
48

p-value
All
trees
0.000
0.504
0.485
0.440
0.864
0.538
0.508
0.798

df

Time
Time * Clone
Time* Shade
Time*Weevil
Time*Clone* Shade
Time *Clone * Weevil
Time* Shade * Weevil
Time*Clone *Shade * Weevil
Error

M Sheight All
Trees
15646.552
21.526
34.949
28.808
6.974
18.281
32.658
10.787
47.512

MS - height
Un-Attacked
Trees
13915.713
1.459
70.144
19.009
4.000
18.654
13.764
2.472
45.445

p-value
Un-attacked
trees
0.000
0.859
0.226
0.521
0.916
0.525
0.740
0.947

Source

1
2
1

MS - height
Un-Attacked
Trees
1453.192
172.177
203.551

p-value
Un-attacked
trees
0.022
0.514
0.377

1
1
2
1
2
1
2
2
41

Time was the only significant variable for within subject testing as the trees grew in height
over the summer, but time by clone was not significant, and there were no interactions (Table
4.2b). Clone 1-1026 was taller than 107-1930 in 2000 and 2001, but only among trees that were not
successfully attacked by the weevils (Table 4.3).

56

Table 4.3 Mean height (cm) for clones 1-1026 and 107-1930 at North Willow; mean overall,
mean o f successfully attacked trees in 2001 and unsuccessfully attacked trees in 2001 for
2000 and 2001.
107-1930
1-1026
2001
2001
2000
2000
2001
2001
2000
2000
1-1026
Not
Not
Mean'
Mean'
Mean
attacked^
Mean'
attacked^ attacked^
attacked^
23
7
n
30
7
30
23
30
30
86.0
86.0
80.0
95.0
102.0
78.0
93.0
Min
77.0
116.0
119.0
148.0
129.0
148.0
117.0
Max
119.0
146.0
102.3
123.2
117.2
126.7
94.4
Mean
101.0
100.2
118.2
4.7
2.4
2.7
5.9
2.4
1.8
SE
2.2
2.5
Mean height o f all trees in sample
^ Mean height o f trees with leaders were killed from weevils
^ Mean height o f trees with leaders that were not killed from weevils

Mean height-increment, for clone 1-1026 in 2000 was 31.6 cm, compared to 24.9 cm for
clone 107-1930 (Table 4.4). In 2001, clone 1-1026 had the same growth increment as 107-1930
when comparing all trees.

Table 4.4 Height increment' (cm) for clones 1-1026 and 107-1930 at Nort 1 Willow.
1071-1026
1930
2000
2001
2000
2001
2001
2000
2001
not
not
attacked^
Mean'
attacked^
Mean'
Mean'
attacked^
attacked^
30
7
30
n
23
7
23
30
30
Min
21.0
21.0
23.0
3.0
3.0
3.0
15.0
0.0
Max
47.0
35.0
47.0
44.0
26.0
44.0
34.0
36.0
Mean 31.6
30.0
32.0
22.2
13.9
24.7
24.9
23.8
SE
1.1
2.0
1.3
1.8
2.7
2.0
1.0
1.5
Mean growth increment o f all trees in sample
^ Mean growth increment o f trees with leaders were killed from weevils in 2000
^ Mean height o f trees with leaders that were not killed from weevils in 2000

Basal diameter was not significantly different between clones in 2000, but was
significantly different for measurements taken on the 2001 leader (Tables 4.5 & 4.6). Shade and
weevil seeding did not affect 2001 leader basal diameter and there were no interactions (Table 4.6).

57

Table 4.5 Analysis o f variance results for leader basal diameter (2000 leader) in
Source

SS

df

MS

F

Clone
Error

0.096
1.456

1
58

0.096
0.025

3.824

Pvalue
0.055

Table 4.6 Analysis o f variance results for leader basal diameter (2001 leader) in
August 2001 at North Willow
Source
SS
df
MS
F
Pvalue
0.164
1
0.164
7.345
0.009
Clone
0.121
2
0.061
2.718
0.076
Shade
0.006
1
0.006
0.290
0.593
Weevil
Clone*Shade
Clone* Weevil
Shade* Weevil
Clone* Shade* Weevil
Error

0.004
0.003
0.047
0.006
1.072

2
1
2
2
48

0.002
0.003
0.024
0.003
0.022

0.079
0.137
1.057
0.138

0.924
0.713
0.355
0.872

None o f the trees o f clone 107-1930 seeded with weevils was attacked successfully, and no
other trees within the block area, exhibited any signs o f attack by weevil. There were five
successful attacks on clone 1-1026 o f the 15 weevil-seeded trees and one o f the non-seeded trees
was attacked by weevils in 2001. In addition, 14 other trees from clone 1-1026 that were not part of
the selected sample but were within the block boundary, were also attacked by weevils, from the
surrounding area or weevils that had escaped from the experiment.
No relationship was found between level o f shade and number o f successful attacks.
However, significant relationships were found between shade and number o f oviposition punctures
for both clones from the fourth sampling day until the last sampling day, June 5-July 17,2001(JD
156-198) in trees o f clone 1-1026 (Figure 4.1,4.2 & 4.3).

58

-107-1930 -#-11026

Degree-days
500.0
4496450.0
400.0
350.0 U

I

300.0 I
250.0 “

j

200.0 £

150.0 E
100.0

50.0
0.0
137

142

149

156

163

170

177

184

198

May-17

May-22

May-29

Jun-05

Jun-12
Date

Jun-19

Jun-26

Jul-03

Jul-17

Figure 4.1 Mean oviposition punctures recorded on each sampling date for clones 1-1026 and 1071930, and accumulating degree-days above 5°C by sampling date at North Willow. May 17-July
17,2001 (JD137-198).

■Open -B-Light

Heavy

14
12

I
I

10

8
6

4
2
0

137

142

149

156

163

170

177

184

198

May-17

May-22

May-29

Jun-05

Jun-12
Date

Jun-19

Jun-26

Jul-03

Jul-17

Figure 4.2 Mean oviposition punctures recorded on trees o f clone 1-1026 by sampling date for each
shade treatment (Open, Light, Heavy) at North Willow. May 17-July 17, 2001 (JD137-198).

59

■Open - B - Light

Heavy

4.5
3.5

2.5
.Û-

0.5
137

May-17

142

149

156

163

170

177

184

198

May-22

May-29

Jun-05

Jun-12
Date

Jun-19

Jun-26

Jul-03

Jul-17

Figure 4.3. Mean oviposition punctures recorded for trees o f clone 107-1930 by sampling date for
each shade treatment (Open, Light, Heavy) at North Willow. May 17-July 17, 2001 (JD 13 7-198).

A significant relationship was also found for distance o f oviposition between the tip of the
terminal and the lowest oviposition puncture and shade treatment, from the second sampling day
May 22 (JD 142) to the last sampling day July 17 (JD 198) in clone 107-1930 (Table 4.7a).

Table 4.7 Kruskal-Wallis test for significance results between shade treatments
for distance between the tip o f the terminal and the lowest oviposition puncture
for each sampling date for clones 1-1026 and 107-1930 at North Willow
a)between three shade treatments and b)-d) Mann Whitney tests between each
shade treatment:
a) between three shade treatments; open, light and heavy
1-1026
107-1930
Kruskal-Wallis
Kruskal-Wallis
Test statistic p-value Test statistic p-value
Sampling date (JD)
df
0.000
1.000
2
0.000
1.00
May 17 (137)
0.041
May 22 (142)
2
2.293
0.318
0.980
5.790
8.314
0.016
May 29 (149)
0.055
. 2
2
6.520
0.038
9.871
0.007
June 5(156)
9.114
2
6.982
0.03
0.010
June 12 (163)
2
6.656
0.036
9.114
0.010
June 19(170)
0.036
9.114
6.656
0.010
June 26 (177)
2
0.036
9.114
July 3 (184)
2
6.656
0.010
2
6.656
0.036
9.097
0.011
July 17(198)

60

b) Mann-Whitney test for difference in distance of oviposition punctures for open and heavy
shade treatments.
1-1026
107-1930
Sampling date
Mann-Whitney ChiMann-Whitney Chi(JD)
df U test statistic square p-value U test statistic square p-value
May 17 (137) 1
12.5
0.000 1.000
12.5
0.000
1.000
May 22 (142) 1
5.5
0.022
2.291 0.130
12.0
0.881
May 29 (149) 1
5.0
2.470 0.116
0.00
6.902
0.009
June 5(156)
1
2.5
4.444 0.035
0.00
6.902
0.009
0.0
June 12 (163) 1
6.902 0.009
0.00
6.902
0.009
June 19 (170) 1
0.0
6.902 0.009
6.902
0.00
0.009
0.0
June 26 (177) 1
6.902 0.009
0.00
6.902
0.009
July 3 (184)
1
0.0
6.902 0.009
0.00
6.902
0.009
0.0
July 17(198) 1
6.902 0.009
0.00
6.860
0.009

c) Mann-Whitney test for differences in distance o f oviposition punctures for open and light
shade treatments.
1-1026
107-1930
Sampling date
Mann-Whitney ChiMann-Whitney Chi(JD)
df U test statistic square p-value U test statistic square p-value
May 17 (137) 1
12.5
0.000
1.000
12.5
0.000 1.000
0.637
May 22 (142) 1
10.5
0.223
12.0
0.881 0.881
3.0
3.938
May 29 (149) 1
0.047
10.0
0.287 0.592
June 5(156)
1
3.0
3.938
0.047
5.5
2.205 0.138
June 12 (163) 1
3.578
3.5
0.059
4.5
2.827 0.093
June 19(170) 1
4.5
2.880
0.090
4.5
2.827 0.093
June 26 (177) 1
4.5
2.880
0.090
4.5
2.827 0.093
July 3 (184)
1
2.880
4.5
0.090
4.5
2.827 0.093
July 17(198) 1
4.5
2.880
0.090
4.5
2.810 0.094

d) Mann-Whitney test for differences in distance o f oviposition punctures for light and heavy
shade treatment.
1-1026
107-1930
Sampling date
Mann-Whitney ChiMann-Whitney Chi(JD)
df U test statistic square p-value U test statistic square p-value
0.000
May 17 (137) 1
12.5
1.000
12.5
0.000 1.000
May 22 (142) 1
8.5
0.743
0.389
0.022 0.881
13.0
May 29 (149) 1
20.0
2.470
0.116
4.870 0.027
2.0
June 5(156) 1
19.0
1.855
0.173
1.0
5.806 0.016
15.0
0.274
June 12 (163) 1
0.600
3.0
3.962 0.047
11.0
June 19(170) 1
0.099
0.753
3.0
3.962 0.047
11.0
0.753
3.962 0.047
June 26 (177) 1
0.099
3.0
July 3 (184) 1
11.0
0.753
3.962 0.047
0.099
3.0
July 17(198) 1
11.0
0.099
0.753
3.0
3.962 0.047

61

The test between open and heavy shade treatment showed the greatest level o f significance
in oviposition distance for all sampling dates (Table 4.7b). The effects between open and light
shade treatment were only different in the third and fourth weeks (May 29 and June 5) o f sampling
for 1-1026 but showed no difference in any dates in 107-1930 (Table 4.7c). The effects between
light and heavy shade treatment were not different in any of the weeks for 1-1026 but were different
in all but the first weeks for 107-1930 (Table 4.7d).
The total number o f oviposition punctures did not vary significantly by shade but did vary
significantly by clone. Rate appeared to peak between 29 May and 12 June, 2001 when degreedays above 5°C were between 112.0 and 202.1°C. The rate o f oviposition appeared different by
shade treatment in clone 1-1026 but not in 107-1930 (Figures 4.2 & 4.3). Rates in 1-1026 appeared
to be greatest for the heavy shade treatment on June 5 and June 12 (JD 156 and 163). The open
treatment appeared to have the lowest overall oviposition rate for 1-1026 (Figure 4.2).
There was no difference in the total number o f predators and parasites found within the
shade treatments in either clone. Because no leaders were killed from attacks by weevil in clone
107-1930, no adult weevils emerged from trees o f this clone. Mean number o f adult weevils that
emerged from each leader did not vary by shade in 1-1026.
Bud-development o f spruce in clone 1-1026 progressed faster than clone 107-1930 at North
Willow (Figure 4.4).

62

0107-1930 LD □ 107-1930 LAT 01-1026 LD 01-1026 LAT

142

149

May-22

May-29

156

163

170

177

Jun-05
Jun-12
Sampling Date

Jun-19

Jun-26

Figure 4.4 Mean Bud-flush classes o f leaders (LD) and laterals (LAT) for clones 1-1026 and 1071930 at North Willow over 8 weeks: May 17-July 3 2001. Bud-flush class: (1) shiny conical (2)
shiny/swollen (3) light brown/swollen (4) columnar (5) split (6) brush (7) feather (8) growing
shoot. Detailed description of bud-flush classes are given in methodology section 4.3.

Lateral and terminal leader development within each clone was similar. However, bud
development of the leaders was significantly different between clones in all but the third and fourth
weeks of sampling (Table 4.8).

Table 4.8 Mann-Whitney results showing differences between clones 1-1026 and
107-1930 at North Willow, for bud development; leaders (LD) and first whorl
lateral (LAT).
Leaders (LD)
Laterals (LAT)
Sampling Date (JD) Chi-Square
p-value
Chi-Squiare
p-value
May 17(137)
7.552
0.006
4.214
0.040
May 22 (142)
15.233
0.000
5.659
0.017
May 29 (149)
0.094
0.759
5.671
0.017
June 5(156)
0.439
0.508
3.687
0.055
June 12 (163)
6.017
0.014
8.866
0.003
June 19 (170)
14.450
0.000
8.536
0.003
June 26(177)
11.800
0.001
1.000
0.317
July 3 (184)
0.000
1.000
0.000
1.000

63

Lateral development was significantly different from the first to third weeks, May 17-29
(JD 137-149) as well as the fifth and sixth weeks June 12-19, 2001 (JD 163-170).
Between May 12-August 29, 2001 (JD 132-241) there were 769.3, 711.0 and 675.5
degree-days above a threshold 7°C in the open, light and heavy shade treatments respectively.
Average light intensity (PAR) recorded for each day under different shade treatments is seen in
Figure 4.5.

-Open•-o -■
LightShade

-HeavyShade

850
750
650
<
_ 550
E 450
DC

< 350

JulianDay

Figure 4.5 Mean daily light intensity (PAR) under shade treatments and in the open at North
Willow site, 2001.

4.3.2 - U pper F raser, Weevil-Seeded Blocks
Height differed significantly by clone at this site (Table 4.9a). Within-subject tests, with
time incorporated into the model, revealed that clone was a significant factor over time (Table
4.9b).

64

Table 4.9 Repeated measures analysis o f variance results for height in 2000 and
2001, for clone and weevil seeded trees and their interactions at Upper Fraser, a)
between subjects and b) within subjects.
a) Between Subjects
df
F
p-value
Source
SS
MS
43421.880
1
Clone
43421.880
42.213
0.000
55.444
1
55.444
0.054
Weevil
0.818
1
Clone*Weevil
173.461
173.461
0.169
0.684
37030.922
36
1028.637
Error
b) Within Subjects
Source
Time
Time * Clone
Time*Weevil
Time*Clone* Weevil
Error

SS
26245.012
308.113
2.112
112.813
1792.450

df
1
1
1
1
36

MS
26245.012
308.113
2.112
112.813
49.790

F
527.111
6.188
0.042
2.266

p-value
0.000
0.018
0.838
0.141

There were no interactions between other independent variables. On average clone, U284
performed better in terms o f height (Tables 4.10 & 4.11).
Table 4.10 Mean height (cm) for clones U284 and J974 in 2000 and 2001 at Upper Fraser.
U284
J974
2000
2001
2001
2000
2001
2001 (notMean*
(not-attacked)^ Mean*
Mean*
Mean*
attacked)^
20
n
20
10
20
20
18
132.9
181.4
Min
163.6
93.4
116.7
116.7
Max
205.4
242.5
214.0
214.0
243.3
168.0
Mean
162.1
202.2
203.3
119.4
151.7
152.0
5.1
5.4
6.1
SE
19.5
23.8
25.1
' Mean height o f all trees sampled
^ Mean height o f trees with leaders that were not killed from weevils

Table 4.11 Height increment (cm) for clones U284 and J974 in 2000 and 2001 at Upper Fraser
U284
J974
2001
2000
2001
2000
2001
2001 (notMean*
Mean*
(not-attacked)^ Mean*
Mean*
attacked)^
10
n
20
20
20
20
18
26.0
15.0
29.0
21.1
19.0
19.0
Min
64.2
56.0
56.0
46.0
46.0
Max
47.0
46.4
43.3
40.2
32.4
32.3
32.6
Mean
0.5
0.6
1.0
1.4
1.7
1.8
SE
Mean height increment o f all trees sampled
^ Mean height increment o f trees with leaders that were not killed from weevils

65

Leader basal diameter did not vary significantly between clones for the 2000 leadergrowth. There was, however, a significant difference between basal diameters in 2001 (Table 4.12).
The weevil-seeding treatment did not affect diameter growth, nor was there an interaction between
weevil-seeding and clone. This indicated that differences in the basal-girth o f the 2001 leader
between clone, were present due to selection o f the trees, or some other extraneous variable, and
not due to weevil-seeding.

Table 4.12 Analysis of variances results for leader basal diameter (2000 leader) in May 2001

2000 Leader

2001 Leader

Source
Clone
Weevil
Clone* Weevil
Error
Clone
Weevil
Clone* Weevil
Error

SS
0.014
0.003
0.020
0.089
0.001
0.056
0.601

df
1
1
1
36
1
1
1
36

MS
0.014
0.003
0.020
0.014
0.089
0.001
0.056
0.017

F
1.052
0.211
1.476

p-value
0.312
0.649
0.232

5.352
0.066
3.326

0.0270
0.799
0.076

Clone U284 sustained more successful attacks than J974; with 7 attacks on U284 and 3 on
J974 respectively. Three un-seeded control trees were also attacked successfully in U284. Five
additional trees, not within the selected sample were also attacked successfully within the block of
clone U284 and three additional trees not within the selected sample were attacked in the J974
block. Mean number o f oviposition punctures also differed between each clone (Table 4.13).

Table 4.13 Mean number o f oviposition punctures for

n
Min
Max
Mean
SE

U284
10
1.0
107.0
52.8
12.9

J974
10
0.0
30.0
5.6
3.6

66

The rate o f oviposition between the two clones at this site appeared different (Figure 4.7).
■U284

J974

170

177

184

198

Jun-19

Jun-26

Jul-03

Jul17

14
12

£

i 8

I

6
4
2

0
144

151

156

163

May-24

May-31

Jun-05

Jun-12
Date

Figure 4.6 Mean oviposition punctures by sampling date for Clones U284 and J974 at Upper
Fraser, calculated by mean difference in weekly oviposition punctures per sampling date, May 24July3,2001 (JD144-198).

Total number of parasites and predators differed significantly by clone (Table 4.14).

Table 4.14 Mean number o f predators and parasites and weevils emerged from U284 at Upper
Fraser.
U 284
J974
Predators &
Weevils
Predators &
Weevils
Parasites
Emerged
Parasites
Emerged
n
10
10
10
10
Min
0.0
0.0
0.0
0.0
Max
32.0
6.0
5.0
0.0
Mean
3.4
1.9
1.0
0.0
0.61
SE
2.53
5.88
0.00

No adult weevils emerged from clone J974 even though attack by weevils resulted in three
dead leaders in this clone.
Bud-development between clone differed significantly between the first and fourth week of
sampling (Table 4.15), but lateral bud development did not differ significantly between clones on

67

any o f the sampling dates. For most sampling dates, leader and lateral development within each
clone was similar (Figure 4.7).

Table 4.15 Differences between clones J974 and U284 for bud development, leaders (LD) and
Sampling Date
(JD)
Week
1
2
3
4
5
6
7
8

Leaders (LD)
Chi-Square
14.832
0.219
3.016
4.016
2.773
1.000
0.000
0.000

May 24 (144)
May 31 (151)
June 5(156)
June 12 (163)
June 19(170)
June 26 (177)
July 3 (184)
July 17(198)

Lateral (LAT)

p-value
0.000
0.639
0.082
0.045
0.096
0.317
1.000
1.000

Chi-Square
0.223
0.205
0.193
1.013
1.334
1.000
0.000
0.000

p-value
0.637
0.651
0.661
0.314
0.248
0.317
1.000
1.000

IU284 LD OU284 LAT ■ J974 LD ■ J974 LAT

S% 5
Ü

I
1 -4

0

-

144

151

156

163

170

177

184

198

May-24

May-31

Jun-05

Jun-12
Jun-19
Bud-Flush Class

Jun-26

Jul-03

Jul-17

Figure 4.7. Mean Bud-flush classes o f leaders (LD) and laterals (LAT) for clones U284 and J974
at North Willow over 8 weeks: May 24-July 17 2001. Bud-flush class: (1) shiny conical (2)
shiny/swollen (3) light brown/swollen (4) columnar (5) split (6) brush (7) feather (8) growing
shoot. Detailed description o f bud-flush classes are given in methodology section 4.3.

68

4.3.3 Results -Upper Fraser, 8-block survey
Height differed significantly in 2000 and 2001 by nursery and for all mixes o f clone and
seedlot sampled (Tables 4.16 & 4.17).

Table 4.16 Height (cm ±SE) in 2000 and 2001, height increment (cm ±SE) 2001 and percentage
of trees attacked by weevils historically, in 2000 and in 2001 for Upper Fraser blocks; Feltons
Height
% Attack % Attack % Attack
Increment
Nursery (Percent
2000
2001
History
2000
2001
2001
o f clone U 185)'
25.8(1.6)
8
2
2
71.0(3.2) 97.3 (3.8)
GT-1 ( 100%)
25.7 (2.6)
16
8
10
85.4(4.0) 112.0 (5.1)
G T-2(67% )
30.3 (1.9)
16
96.6 (3.6) 126.9 (4.5)
8
8
GT-3 ( 33%)
135.2
(5.2)
30.0
(3.2)
20
105.3
(4.3)
8
4
GT-4 ( 0%)
33.2 (2.9)
2
2
86.5 (3.5) 120.2 (5.0)
4
PL-1 (100%)
32.0 (3.0)
12
4
89.5 (3.4) 121.5(4.3)
8
PL-2 (67%)
24
43.8 (6.9)
8
4
101.3 (5.4) 147.7 (9.2)
PL-3 (33%)
35.6 (4.0)
4
PL-4 (0%)
123.1 (3.3) 158.7 (3.1)
40
38
’ Blocks were planted by percent of clone U 185 in 100, 67, 33 and 0 % clone with remaining
portion planted with trees from seedlot 6864. Clones and seedlings from seed-lot stock were
inter-mixed in blocks that were not 0 or 100%.

Table 4.17. Repeated measures analysis o f variance results for height in 2000 and 2001, for
nursery, percent clone o f U 185 and their interactions at Upper Fraser, a) between subjects and b)
within subjects.
a) Between subjects

Nurseiy
% Clone
Nursery * % Clone
Error

Sum-ofSquares
44631.491
158696.744
6219.461
711609.235

df

Mean-Square

F-ratio

p-value

1
3
3
38
5

44631.491
52898.915
2073.154
1848.336

24.147
28.620
1.122

0.000
0.000
0.340

df

Mean-Square

F-ratio

p-value

1
1
3
3
385

201697.716
3296.964
683.873
156.498
290.668

693.911
11.343
2.353
0.538

0.000
0.001
0.072
0.656

b) Within subjects

Time
Time* Nursery
Time* % Clone
Time* Nursery * % Clone
Error

Sum-ofSquares
201697.716
3296.964
2051.620
469.494
111907.169

69

There was a significant difference in height-growth between the two nurseries (Table
4.17a) with Peltons having a greater height increment (Table 4.16). Within-subject testing revealed
only nursery to be significantly different over time, while percent clone was not (Table 4.17b).
However, height increment did not vary significantly between the clone and seedlot plmiting
mixtures. Rates o f attack differed significantly by percentage o f clone in blocks planted with trees
from Peltons but not in the Green Timbers blocks in 2000 (Table 4.17). Evidence o f attack-history
differed between the percentage of clone with the greatest and least rates o f attack in the 0% and
100% clonal blocks respectively.

70

4.4 Discussion
4.4.1 Growth of Spruce and Incidence of A ttack by Weevils
Clone 1-1026 had a larger height increment than 107-1930, which was not expected
according to prior rankings for growth (Table 4.1). At Upper Fraser, clone U284 had a larger height
increment than J974 even though both clones were ranked similarly for growth. The clones that
grew fastest at both sites had the highest levels o f weevil-attack. Clone 1-1026 was ranked lower in
terms o f weevil resistance than 107-1930, and appeared to perform accordingly, as no trees from
clone 107-1930 were attacked. However, within the entire breeding population (173) both clones
chosen at North Willow were ranked relatively high for weevil resistance (Table 4.1).
The ability o f clone 107-1930 to resist attack by weevil may override its open-growing
locale. The lowest ranked clones in this study, U185 and U284 performed poorly in terms of
resistance to weevils. Clone U284 at Upper Fraser sustained the greatest number o f attacks on trees
that had been weevil-seeded. However, 1-1026, at North Willow, had the greatest number o f attacks
by weevils on trees that were not seeded. This could be due to the adjacent spruce progeny-trial,
which appeared to have a high rate o f attack within the block. Clone J974, which had a relatively
low paternal ranking for resistance to weevils, did not have a high rate o f attack.
The 8-block trial at Upper Fraser, with varying mixtures o f seedlot trees and cloned trees,
were significantly different in height and growth. Clone U185 performed poorly, in terms of
growth, in comparison to the seedlot stock. This was surprising as U284, which had the same
resistance-ranking as U 185, grew faster than J974, even though both trials were located within 150
m. However, differences in site-series may have been present between the two trials.

4.4.2 Artificial Shade and Overstorey
No significant relationship was found between leaders killed by weevils and shade
treatments at North Willow. Several reasons may account for this finding. Sullivan (1961) noted
that one of the main differences between shaded and open stems was that shaded stems were

71

thinner. In my experiment at North Willows, the trees had been growing in the open since planting
and had not developed thinner leaders on which the weevils were placed. Any altered properties of
the leader, either physical or chemical, resulting from the shade treatments would not be seen until
at least the following season. The weevils would therefore not respond to the leader in the same
manner as if it had been growing in reduced light conditions over several years.
At North Willow, a significant relationship was found with the distance o f oviposition and
shade treatment, the greatest dispersal o f oviposition punctures were on trees under shade
treatments compared to the open. This is commensurate with findings in the Pass Lake study
(Chapter 3). This evidence appears to support findings by Sullivan (1961). However, successful
attack was not related to shade treatment. This was shown by examining the differences in
oviposition punctures by sampling date under each shade treatment. The number o f oviposition
punctures was not reduced by the shade treatments. In addition, the number o f adult weevils
emerging by shade treatment did not vary, which would be expected if shade treatment had an
effect on brood development. Sullivan (1961) also observed that the weevils under shade fed and
oviposited beyond the terminal leader, but in my experiments weevils did not oviposit beyond the
leader.
The variable findings for the shade experiments may be a result o f many factors within the
experimental design itself. As in Sullivan’s (1961) study, the weevils were placed on the leaders
and did not choose the host themselves. However, the neutral density shade cloth does not have the
same physical properties as a deciduous canopy which would alter the spectral properties beneath
it. The shade cloth merely reduces the intensity o f light, whereas a deciduous canopy alters both
intensity and quality o f light. I hypothesize that if the experiment were to be modified using either
a natural canopy o f deciduous trees, or material with similar spectral properties, more varied and
conclusive results regarding oviposition behaviour o f weevils would be found.
Another source o f the conflicting results may be that the weevils were not caged, as in
Sullivan’s (1961) trials, and therefore were free to leave undesirable trees, be preyed on, or blown

72

away in extremely windy conditions. It is debatable if Sullivan’s (1961) weevils would have stayed
on the trees and fed in this manner if they were not caged on the tree itself. Other sources
confounding the results may arise from the physical properties o f the shade cloth. Even though the
cloth was porous, temperatures were not greatly reduced under the shade treatments, as would be
the effect under some types o f natural canopy. During the early oviposition period in May, average
daily temperature was sometimes greater under the shade. This could be due to the insulating effect
of the dark shade cloth which kept temperatures warmer during the night, resulting in a higher
average over the 24-hour period.

4.4.3 Bud-development of Spruce
Hulme (1995) noticed that in Sitka spruce clones, generally the least damaged trees, by P.
strobi, initiated apical bud development earlier in the season relative to susceptible clones. Alfaro
et al. (2000) found that budburst development was under strong genetic control and that on average
spruce families with resistance to attack by weevil initiated and maintained a faster rate o f bud
development than families from susceptible parents. However, there was considerable overlap
between resistant and non-resistant families (Alfaro et al. 2000). At North Willow, trees from clone
1-1026, which had the lower maternal and paternal rankings for resistance to weevils, developed
sooner than trees from clone 107-1930, but had a higher incidence of attack from weevils. This
supports the general findings o f Hulme ( 1995) and Alfaro et al. (2000) that phenology and
resistance o f spruce are not always related. There may be species differences between Sitka and
interior spruce, as differences were seen between lag-time between leader and lateral bud-break.
Alfaro et al. (2000) found that lateral buds in Sitka spruce develop sooner than leaders. At North
Willow, lateral bud-development in interior spruce clones lagged behind leader bud-development
for the first few weeks (Figure 4.4) and then caught up to leader phenology. However, this may be
due the effects o f water availability, or lower spring temperatures, rather than a specific species
difference between the spruces.

73

At Upper Fraser, the leaders and lateral from J974 developed sooner, and had fewer
successful attack by weevils than U284. These clones both had moderate resistance rankings and it
is therefore difficult to delineate whether or not the more resistant clone developed sooner. The
reason for the difference between 1-1026 and 107-1930 may be a consequence o f the unknown
basis for the original ranking of resistance to weevils. Resistance, is based upon many traits and
different mechanisms, which may or may not be related to bud phenology (Kiss and Yanchuk
1991 ; Alfaro et al. 2000). Planting location may also play a role, as the site at Upper Fraser
appeared to be richer and more productive, while the site at North Willow appeared less
productive. Budburst phenology is also influenced by heat, both air and soil, and water availability
(Dormling ef a/. 1968).
Although bud-burst phenology did not correlate with resistance, the rankings for resistance
did follow closely with their original status; U284, was the clone with the most numerous leaders
killed due to attack by weevils followed by 1-1026 and then J974. Clone 107-1930 had no
incidence o f attack by weevils in the study as well as no incidence of attack outside of the
randomly selected trees.

4.5 Conclusions
There appeared to be a strong genetic component for resistance to weevil in clone 1071930, but not in the other clones. It is unknown what the trait, or traits, of resistance were
functional in clone 107-1930. Bud-development did not appear to relate to any resistance
mechanism in the clones studied. Further studies, utilizing a larger number o f clones, need to be
done to determine if mechanisms relating to bud-flush, are shown in interior spruce that influence
resistance to weevils. Shade may play a role in behaviour of weevils, but the results from this study
are inconclusive. Further studies using shade, which simulate changes in light quality, need to be
done on interior spruce in order to determine what role light plays in influencing the ovipositionbehaviour o f Pissodes strobi.

74

CHAPTER 5

Conclusions and Recommendations

5.1 Summary and integration of major findings
The overall objective o f this study was to determine if shade, or lowered light levels,
created by natural or artificial treatments, reduced rates o f attack by the white pine weevil on
interior spruce trees. Data collected at Sinclair Mills, where natural overstorey created by paper
birch lowered rates o f attack by the weevil in a 13-year old spruce plantation, supported previous
studies regarding such mitigating effects. However, this was not found in the studies using artificial
treatments to create shade over young spruce seedlings. The latter were used in the spruce-family
trial at Pass Lake in the summer o f 2000 and the spruce clonal studies at North Willow in 2001.
The main difference, between the artificial and natural shade, was the effect on the quality o f light
transmitted. The spectral distribution was altered under natural conditions, but remained unchanged
under artificial conditions. Near infrared wavelengths became more prominent under birch trees,
while shorter wavelengths were reduced.
At Sinclair Mills, the primary objectives were to 1) quantify growth o f spruce and rates of
attack by weevils in the control and open stands four years after vegetation removal with
glyphosate, and 2) follow attack-rates by weevils over the two-year study period. Percentage of
attack by weevils was significantly less on interior spruce and height-growth o f spruce was
significantly better in the control area compared to the open area, previously treated with herbicide.
Secondary objectives at Sinclair Mills were to quantify the effects o f birch overstorey on
open and shaded spruce trees as differences in light and temperature. The shape o f the crown in
paper birch allowed substantial amounts o f light through the canopy. Light was reduced on average
23% in the control area after completion of deciduous bud-break. However, because paper birch
within the plantation was not uniformly dispersed, percentage o f full light varied greatly. Light

75

quality was also different under the birch canopy compared to the open. Temperature was different
between open and shaded trees but average daily air temperature at the leader did not differ greatly
between shaded and open trees. This however, may be a limitation of the experimental design and
placement o f the temperature sensors. Birch densities in the control ranged from 700 to 3500 sph
and maximum total (spruce plus birch) densities were 3465 sph.
Stands in the control area would not meet current free-growing definitions due to
competition and the treated area would not be classed as free- growing due to attack by weevil.
Competition at the observed densities did not reduce growth o f spruce and the overstorey appeared
to reduce levels o f attack by white pine weevil. Others, (Simard and Hannam 2000) have found that
paper birch self-thins rapidly when growing in mixed stands. Initial densities o f paper birch o f up
to 60,000 sph were reduced to an average of 6000 sph by age 10, and 1500 sph by 15 yrs in the
ICH Biogeoclimatic zone (Simard and Vyse 1994). Upper and lower bounds o f birch stocking for
enhancing spruce growth in the SBS have yet to be delineated. The growing environment for
spruce, created by the paper birch overstorey probably played a role in reducing incidence of attack
by weevils in the control area. However, further studies are necessaiy to determine specific
mechanisms which result in reduced incidence o f attack on spruce under a birch canopy.
The study at Sinclair Mills confirms previous hypotheses that predict the removal of
broadleaf competition, to enhance conifer growth, may result in increased rates o f attack by
weevils (Lanier 1983; Alfaro et al. 1994). When the deciduous competitor species were removed,
incidence o f attack by weevils was much higher in the open, treated area. It is hypothesized that the
re-growth o f paper birch into the plantation, after sheep grazing to remove vegetation, had a
negative effect on the already present population o f weevils. Because glyphosate targets the
shikimic acid pathway in plants (Stasiak et al. 1992) it is highly unlikely that the herbicide directly
affected weevil physiology, and the influence on population-growth was likely due to abundance of
food, breeding sites, and microclimate.

76

Both treated and untreated stands had substantial evidence of previous attack, yet
populations o f weevils in each area must have diverged after treatment. The primary variable
affecting this change was the presence o f birch which created overstorey shade. The lack of birch,
or other deciduous species, in the treated area created favourable habitat for the weevils in several
ways. Snow in the treated area melted sooner than in the control area, allowing ground
temperatures to warm the sites where weevils overwinter. The absence o f birch in the area treated
with herbicide would have allowed weevils a clear view o f the leader. Shaded spruce leaders under
the birch canopy may have had thinner bark or increased resin canal density, a primary defence in
spruce against weevil (Tomlin and Borden 1997b).
The main objectives for the studies at Pass Lake and North Willow, were to determine the
effects of artificial shade on initial attack by weevils placed on planted spruce seedlings at the tree,
family and clone level. It was thought that weevils under shade, without having to find a host tree,
would oviposit at a normal rate and pattern unimpeded by reduced light intensity. However, the
shade treatments at Pass Lake and North Willow caused the weevils to oviposit in a dispersed
pattern. This result did not appear to affect overall development o f insects in the light shade
treatment under which the greatest number o f successful attacks occurred. Lowered light intensity,
or greater shade level also did not reduce growth o f the selected families of spruce, which is
consistent with findings from Logan (1969).
A detailed data collection at North Willow revealed that although the shade treatment
caused a change in the dispersion o f oviposition punctures there was no impact on the number per
tree.

5.2 Experimental benefits, design and liabilities
Temperature is inextricably linked to the intensity o f light in field situations, and therefore
cannot be isolated except under laboratory or greenhouse conditions. This was the case for all
studies undertaken within this thesis. Shade created by natural or artificial means ultimately

77

reduces overall temperature accumulation. Therefore, only inferences are made regarding the affect
o f light in a natural setting to the effects o f successful attack by the white pine weevil. Mean daily
temperature, taken at the leader, did not differ greatly between open and shaded trees in Sinclair
Mills. Light samples taken at the leader continuously over the season were much different under
shaded versus open trees. This suggests that light and temperature may be linked more loosely in a
natural setting, compared to laboratory conditions.

5.2.1 Sinclair Mills
Estimates of tree-form between trees from the treated and control areas at Sinclair Mills
were markedly different. These estimates o f damage range from severe to moderate attack, may
however be conservative. Estimates of minor damage were based upon defects occurring above 2
m. Damage such as a fork or severe crook, below 2 m was given the categorical ranking of severe
damage. However, an improvement to this ranking system should incorporate a larger length of
clear bole and implement damage rankings above and below 2.54 or 5.08 m (first two logs), as it
more closely represents the length o f saw timber used in this area. A larger sample size of leaders
may have been more useful to examine parasite populations, as no significance was found when
comparing weevil-infested leaders from open and shaded trees. A data logger set up in the open,
treated area would have been useful to account for temperature differences between the two sites.
In addition, this un-replicated study is limited as plot-replicates controlled for variation in sampling
but not the effects o f treatment.

5.2.2 Pass Lake
Using artificial shade allowed the level, or intensity o f light to be controlled and replicated
many times. Use o f pedigreed families introduced known levels o f resistance. Weevils were not
sexed before seeding which may have caused variation in success of attack, but the probability of
having all males or females on a single tree is only 0.03125, as the sex ratio o f P. -strobi is

78

approximately 50:50. Shade treatments that altered the quality of light as well as the intensity
would aid in determining how light affects oviposition behaviour of weevils on interior spruce. A
follow up study over several years would be useful to determine if traits within families for growth
and resistance are expressed when trees are older.

5.2.3 North Willow
Using SE clones o f spruce at North Willow resulted in no variance in genetic make-up
between individual trees o f the same clone. Therefore, all responses by weevils on the trees should
be attributable to environment. However, the choice o f SE clones was limited because only clones
produced in large numbers were available for deployment (Hawkins, Pers. Comm. 2000). The
design was limited because only two clones were tested with the shade treatments and only one
clone, 1-1026, was attacked successfully by weevils. In addition weevils from the endemic
population attacked trees not seeded in the experiment. The design of the shade structures may
have hindered movement o f the insects by trapping them on the trees under the shade structures.
This study would be o f more relevance if conducted over several seasons. Shade would need to be
installed at least 2 years before the experiment so that trees could adopt characteristics o f sprucetrees growing under natural overstorey. Traits, associated with resistance not expressed during the
trial could be expressed at an older age, and therefore a follow up study o f this site is justified.

5.3 Recommendations
In areas where attack by weevil rates are high, care should be taken when implementing
vegetation management procedures. Birch at levels equal to or less than that found in Sinclair
Mills, at a maximum o f 3500 sph (spruce and birch), should probably be left until trees are of
substantial height to ensure clear, straight saw quality timber in the SBS vk. This would need to be
defined for other subzones in the SBS that are have a high hazard rating for white pine weevil.
Free-growing regulations may need to be revised, as limits for deciduous species may be too low

79

for spruce plantations at risk o f attack by weevils. A results-based Forest Practices Code would be
useful for managing stands with high levels o f attack. Studies also need to be done on the
relationship between light and aspen, as this is a more prominent deciduous species in the Sub
Boreal Spruce Zone (Peterson and Peterson 1995). In addition, aspen has a different crown
structure and area than paper birch. Aspen, present at approximately 1000 sph creates 50% full
light (Comeau 2001) while the study at Sinclair Mills showed that twice as many sph o f birch
resulted in 77% full light.
The use o f families, or clones, known to show resistance to attack by white pine weevil
may be beneficial for deployment in high hazard areas o f the SBS. The families o f spruce at Pass
Lake should be revisited in a follow up study to determine if resistance in spruce, to attack by
weevils, is expressed as trees age. Clones o f spruce may also prove to be useful in an operational
setting. Clone 107-1930, would be of interest for further testing as no individual trees at the site
were attacked by either seeded or endemic weevils. Deployment o f clonal mixtures, rather than
monoclonal blocks, within a plantation may reduce selective pressure on populations o f weevil.
The complexity, dynamics and economic importance o f spruce, and the white pine weevil
and deciduous angiosperm trees in the SBS warrants further study if these stands are to be managed
as a sustainable resource. In the future, commercial productivity may be maximized when, broad­
leaf vegetation is incorporated and managed as a main component within the stand.

80

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Droska, J.S., F.B. Knight and M.W. Houseweart. 1983. Phototactic responses o f the white pine
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Dormling, I., A. Gustafsson and D. von Wettstein. 1968. The experimental control o f the life cycle
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Dormling, I. 1989. The role o f photoperiod and temperature in the induction and release of
dormancy in Pinm sylvestris L. seedlings. Ann. Sol For. 46(Suppl.): 228-232.
Bis, S. 1967. Establishment and early development o f white spruce wildlings and coastal nurseiy
seedlings in the interior of British Columbia. For. Chron. 42:346-349.
Eis, S. 1970. Root-growth relationships o f juvenile white spruce, alpine fir, and lodgepole pine on
three soils in the interior of British Columbia. Environ. Can., Can. For. Serv., Victoria, B.c.,
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Fraser, R.G. and D.G. Heppner 1993. Control of white pine weevil, Pissodes strobi, on Sitka
spruce using implants containing systemic insecticides. For. Chron. 69:600-603.
Farrar, J.L. 1995. Trees in Canada. Fitzheniy & Whiteside Ltd. And the Canadian Forest Service.
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16:192-202.
Graham, S. 1926. The biology and control o f the white pine weevil, Pissodes strobi Peck. Cornell
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Gara, R.I., R.L. Carlson and B.F. Hrutfiord. 1971. Influence o f some physical and host factors on
the behavior o f the Sitka spruce weevil, Pissodes sitchensis, in southwestern Washington. Ann:
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Gara, R.I., Mehary, T. and C. Oliver. 1980. Integrated pest management o f the Sitka-spruce weevil.
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Gordon, J.C. and P R. Larson. 1968. Seasonal course o f photosynthesis, respiration, and
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83

by: R.I. Alfaro, G. Kiss, and R.G. Fraser. Proceedings o f a symposium held January 19-21,
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Prince George B.C. V2N 4Z9.email: hawkinsc@unbc.ca
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84

Hulme, M.A. and J.W.E. Harris. 1988. How Lonchaea corticis Taylor may impact broods of
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British Columbia, Vancouver.

85

Lewis, K, El-Kassaby, Y., Alfaro, R.I., and S. Bames. 2000. Population structure o f the white pine
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90

APPENDIX I
Campbell 21X Micrologger programs

A. 21x Micrologger program for Sinclair
Mills 2001

1:5019 F
2: 13
Z Loc [ LoglD

]

;{21X)

*Table 1 Program
01; 10
Execution Interval (seconds) ;
1: Internal Temperature (P I7)
1:12
L oc[T C _ref ]
2: Thermocouple Temp (SE) (P I3)
Reps
1: 8
15 mV Slow Range
2:2
3: 1
SE Channel
4: 1
Type T (Copper-Constantan)
5: 12
Ref Temp (Deg. C) Loc [ TC_ref

]
6: 1
7: 1.0
8: 0.0

Loc [ Temp 1
Mult
Offset

]

3: Volt(Diff) (P2)
1; 1
Reps
2: 2
15 mV Slow Range
3: 5
DIFF Channel
4 :9
Loc[Q 10183 ]
5: 255.75 Mult
6:0.0
Offset
4: V olt(D iff)(P2)
1: 1
Reps
2: 2
15 mV Slow Range
3: 6
DIFF Channel
4: 10
Loc [ Q10534 ]
5:303.95 Mult
6:0.0
Offset
5: Volt (Diff) (P2)
1: 1
Reps
2: 2
15 mV Slow Range
3 :7
DIFF Channel
4:11
Loc[Q 16883 ]
5:344.83 Mult
6:0.0
Offset
6: Z=F(P30)

7: Batt Voltage (PIO)
1:14
Loc [ Battery ]
8: If time is (P92)
1: 0
Minutes into a
2: 60
Minute Interval
3:10
Set Output Flag High
9: Real Time (P77)
1:1220 Year,Day,Hour/Minute (midnight
= 2400)
10: Sample (P70)
1:1
Reps
2: 13 Loc [ LoglD
11: Average (P71)
1: 11
Reps
2: 1
Loc [ Temp_l

]

]

12: Maximum (P73)
8
Reps
10
Value with Hr-Min
1
Loc [ Temp_l ]
13: Minimum (P74)
8
Reps
10
Value with Hr-Min
1
Loc [ Temp i ]
14: Serial Out (P96)
1:30
SM192/SM716/CSM1
*Table 2 Program
02: 0.0000 Execution Interval (seconds)
*Table 3 Subroutines
End Program
-Input Locations1 Temp_l 1 3 1
2 Temp_2 13 1

91

3 Temp_3

13 1
93 1
5 Temp_5 9 3 1
6 Temp_6 9 3 1
7 Temp_7 9 3 1
8 Temp 8 17 3 1
9Q10183 5 1 1
10Q10534 1 1 1
11 Q 16883 1 1 1
12 TC_ref 1 1 1
13 LogID 1 1 1
14 Battery 10 1
15 _______ _ 0 0 0
16 ________ _ 0 0 0
17 _______ _ 0 0 0
18 ________ _ 0 0 0
19 _______ _ 0 0 0
20 _______ _ 0 0 0
2 1 _______ _ 0 0 0
2 2 _______ _ 0 0 0
23 _______ _ 0 0 0
24 _______ _ 0 0 0
2 5 _______ _ 0 0 0
26 _______ _ 0 0 0
2 7 _______ _ 0 0 0
000
28
-Program Security?
0
0000
0000
4 Tem p_4

Final Storage Label File for: SINCLROl .CSI
Date: 4/23/2001
Time: 10:56:16
108 Output Table 60.00 Min
1 108 L
2 Year_RTM L
3 Day RTM L
4 Hour_Minute_RTM L
5 LogID L
6 Temp l AVG L
7 Temp_2_AVG L
8 Temp_3_AVG L
9 Temp 4 AVG L
10 Temp_5_AVG L
11 Temp_6_AVG L
12 Temp_7_AVG L
13 Temp_8_AVG L
14Q10183_AVG L
15 Q10534_AVG L

16Q16883. AVG L
17 T e m p i .MAX L
18 Temp_l Hr_Min_ MAX L
19 Temp 2 ^MAX L
20 Temp_2 Hr_Min MAX L
21 Temp 3 'MAX L
22 Temp_3 Hr_Min MAX L
23 Temp_4 ^MAX L
24 Temp_4 H r M i n MAX L
25 Temp_5 'm a x L
26 Terap_5 H r M i n MAX L
27 Temp_6 ^MAX L
28 Temp_6 H r M i n MAX L
29 Temp_7 MAX L
30 Temp_7 Hr_Min MAX L
31 Temp_8 MAX L
32 Temp_8_ H r M i n MAX L
33 Temp_l .MIN L
34 Temp_l H r M i n MIN L
35 Temp_2 MIN L~
36 Temp_2 Hr_Min MIN L
37 Temp_3 .MIN L
38 Temp_3 H r M i n MIN L
39 Temp_4 ^MIN L~
40 Temp_4 H r M i n MIN L
41 Temp_5 MIN L
42 Temp_5 Hr_Min_ MIN L
43 Temp_6_ .MIN L
44 Temp 6 H r M i n MIN L
45 Temp_7 ^MIN L “
46 Temp_7 H r M i n MIN L
47 Temp_8_ 'MIN L '
48 Temp_8 Hr Min MIN L

Estimated Total Final Storage Locations used
per day 1152.0
Program Trace Information File for:
SINCLROl.CSI
Date: 4/23/2001
Time: 10:56:16
T = Program Table Number
N = Sequential Program Instruction Location
Number
Instruction = Instruction Number and Name
Inst ExTm = Individual Instruction Execution
Time

92

Block ExTm = Cumulative Execution Time
for program block,
i.e., subroutine
Prog ExTm = Cumulative Total Program
Execution Time
Output
Flag High

Program Table 1 Execution Interval 10.000
Seconds
Table 1 Estimated Total Program Execution
Time in msec 510.9 w/Output 559.8
Table 1 Estimated Total Final Storage
Locations used per day 1152.0

Inst Block Prog
Inst Block Prog
ExTm ExTm ExTm
ExTm ExTm ExTm
T|N|Instruction
(msec) (msec)
(msec) (msec) (msec) (msec)

Ijljl? Internal Temperature
14.0 14.0
14.0 14.0 14.0 14.0
112| 13 Thermocouple Temp (SE) 226.4
240.4 240.4 226.4 240.4 240.4
l|3|2Volt(Difif)
74.9 315.3 315.3
74.9 315.3 315.3
1|4|2 Volt(Diff)
74.9 390.2 390.2
74.9 390.2 390.2
1|5|2 Volt(Diff)
74.9 465.1 465.1
74.9 465.1 465.1
1|6|30Z=F
0.3 465.4 465.4
0.3 465.4 465.4
l|7|10Batt Voltage
7.6 473.0
473.0
7.6 473.0 473.0
1|8|92 If time is
0.3 473.3 473.3
0.3 473.3 473.3
Output Flag Set @ 18 for Array 108
1|9|77 Real Time
0.1 473.4
473.4
1.0 474.3 474.3
Output Data 3 Values
0.1 473.5
1|10|70 Sample
473.5
1.0 475.3 475.3
Output Data 1 Values
1|11]71 Average
6.4 479.9
479.9 35.1 510.4 510.4
Output Data 11 Values
1|12|73 Maximum
14.5 494.4
494.4 23.7 534.1 534.1
Output Data 16 Values
1|13|74 Minimum
14.5 508.9
508.9 23.7 557,8 557.8
Output Data 16 Values
1|14|96 Serial Out
2.0 510.9
510.9
2.0 559.8 559.8

Estimated Total Final Storage Locations used
per day 1152.0

93

B. 21X Micrologger program for Pass
Lake 2000
;{21X}
♦Table 1 Program
01:10
Execution Interval (seconds) ;
1: Internal Temperature (P I7)
1:12
L oc[T C _ref ]
2: Thermocouple Temp (SE) (P13)
1: 8
Reps
2:2
15 mV Slow Range
SE Channel
3: 1
Type T (Copper-Constantan)
4: 1
R ef Temp (Deg. C) Loc [ TC_ref
5: 12

]
6: 1

7: 1.0
8 : 0.0

Loc [ Temp 1
Mult
Offset

1:14

Loc [ Battery ]

8: If time is (P92)
1: 0
Minutes into a
2: 60
Minute Interval
3:10
Set Output Flag High
9: Real Time (P77)
1: 1220 Year,Day,Hour/Minute (midnight
= 2400)
10: Sample (P70)
1: 1
Reps
2: 13
Loc [ LogID

]

11: Average (P71)
1: 11
Reps
2: 1
Loc [ Temp i

]

]

3: V olt(D iff)(P2)
1: 1
Reps
2: 2
15 mV Slow Range
3: 5
DIFF Channel
4: 9
Loc [ Q 16744 ]
5:320.51 Mult
6:0.0
Offset
4: V olt(D iff)(P2)
1: 1
Reps
2 :2
15 mV Slow Range
3: 6
DIFF Channel
4:10
Loc [Q 1 6747 ]
5:331.13 Mult
6:0.0
Offset

12: Maximum (P73)
1: 8
Reps
2:10
Value with Hr-Min
3: 1
Loc [ Temp i ]
13: Minimum (P74)
1: 8
Reps
2: 10 Value with Hr-Min
3:1
Loc [ Temp i ]
14: Serial Out (P96)
1:30
SM192/SM716/CSM1
♦Table 2 Program
02: 0.0000 Execution Interval (seconds)
♦Table 3 Subroutines
End Program

5: V olt(D iff)(P2)
1: 1
Reps
2: 2
15 mV Slow Range
3: 7
DIFF Channel
4:11
Loc [Q 1 1427 ]
5:296.74 Mult
6:0.0
Offset
6: Z=F(P30)
1: 1490 F
2: 13
Z Loc [ LogID
7: Batt Voltage (P I0)

]

-Input Locations1Tempi 13 1
2 Temp_2 1 3 1
3 Temp_3 1 3 I
4 Temp_4 9 3 1
5 Temp_5 9 3 1
6 Temp 6 9 3 1
7 Temp_7 9 3 1
8 Temp_8 17 3 1
9Q16744 5 1 1
10Q16747 1 1 1
11Q11427 1 1 1

94

12 TC_ref 1 1 1
13 LogID 1 1 1
14 Battery 1 0 1
15
000
16
000
17
000
18
000
19
000
20
000
21
000
22
000
23
000
24
000
25
000
26
000
27
000
28
000
-Program Security0000
0000
0000
Final Storage Label File for: PASS 1.CSI
Date: 5/01/2000
Time: 16:31:12
108 Output_Table 60.00 Min
1 106 L
2 Year RTM L
3 Day RTM L
4 Hour_Minute_RTM L
5 LogID L
6 Temp_l_AVG L
7 Temp_2_AVG L
8 Temp_3_AVG L
9 Temp_4_AVG L
10Temp_5_AVG L
11 Temp_6_AVG L
12 Temp_7_AVG L
13 Temp_8_AVG L
14 Light 1_AVG L
15 Light 2_AVG L
16 Light 3_AVG L
17 Light_4_AVG L
18 Temp_l_Hr_Min_MAX L
19 Temp_2_MAX L
20 Temp_2_Hr_Min_MAX L
21 Temp_3_MAX L
22 Temp_3_Hr_Min_MAX L
23 Temp_4_MAX L

24 Temp 4_Hr_Min .MAX L
25 Temp ]S_MAX L
26 Temp 5_Hr_Min MAX L
27 Temp '6_MAX L
28 Temp 6_Hr_Min MAX L
29 Temp ]7_MAX L
30 Temp 7_Hr_Min MAX L
31 Temp X m a x L
32 Temp 8_Hr_Min MAX L
33 Temp j_ M IN l '
34 Temp I H r M i n MIN L
35 Temp 2_MIN l '
36 Temp 2_Hr_Min MIN L
37 Temp 3_MIN L
38 Temp 3_Hr_Min MIN L
39 Temp 4_MIN L
40 Temp 4_Hr_Min MIN L
41 Temp X m i n l '
42 Temp 5_Hr_Min MIN L
43 Temp X m i n l “
44 Temp 6_Hr_Min MIN L
45 Temp X m i n l "
46 Temp 7_Hr_Min MIN L
47 Temp X m i n l '
48 Temp 8 Hr Min MIN L

Estimated Total Final Storage Locations used
per day 455.0
Program Trace Information File for:
PASS 1.CSI
Date: 5/01/2000
Time: 16:31:12
T = Program Table Number
N = Sequential Program Instruction Location
Number
Instruction = Instruction Number and Name
Inst ExTm = Individual Instruction Execution
Time
Block ExTm = Cumulative Execution Time
for program block,
i.e., subroutine
Prog ExTm = Cumulative Total Program
Execution Time
Output
Flag High

95

Inst Block Prog
Inst Block Prog
ExTm ExTm ExTm
ExTm ExTm ExTm
T|N|Instruction
(msec) (msec)
(msec) (msec) (msec) (msec)

111117 Internal Temperature
14.0 14.0
14.0 14.0 14.0 14.0
1|2|13 Thermocouple Temp (SE) 226.4
240.4 240.4 226.4 240.4 240.4
1|3|2 Volt (Diff)
74.9 315.3 315.3
74.9 315.3 315.3
1|4|2 Volt (Diff)
74.9 390.2 390.2
74.9 390.2 390.2
1|5|2 Volt (Diff)
74.9 465.1 465.1
74.9 465.1 465.1
1|6|30Z=F
0.3 465.4 465.4
0.3 465.4 465.4
1|7|10 Batt Voltage
7.6 473.0
473.0
7.6 473.0 473.0
118192 If time is
0.3 473.3 473.3
0.3 473.3 473.3
Output Flag Set @ 18 for Array 108
119177 Real Time
0.1 473.4
473.4
1.0 474.3 474.3
Output Data 3 Values
1110170 Sample
0.1 473.5
473.5
1.0 475.3 475.3
Output Data 1 Values
111 1|71 Average
6.4 479.9
479.9 35.1 510.4 510.4
Output Data 11 Values
1112173 Maximum
14.5 494.4
494.4 23.7 534.1 534.1
Output Data 16 Values
1113174 Minimum
14.5 508.9
508.9 23.7 557.8 557.8
Output Data 16 Values
1114196 Serial Out
2.0 510.9
510.9
2.0 559.8 559.8
Program Table 1 Execution Interval 10.000
Seconds
Table 1 Estimated Total Program Execution
Time in msec 510.9 w/Output 559.8
Table 1 Estimated Total Final Storage
Locations used per day 455.0

96

C. 21X Micrologger program for North
Willow 2001
;{21X}
♦Table 1 Program
01: 10
Execution Interval (seconds) ;
1: Internal Temperature (P I7)
1: 12
L o c[T C _ ref ]
2: Thermocouple Temp (SE) (P13)
Reps
1: 8
15 mV Slow Range
2:2
SE Channel
3: 1
Type T (Copper-Constantan)
4: 1
Ref Temp (Deg. C) Loc [ TC_ref
5: 12

]
6: 1

7:1.0
8 : 0.0

Loc [ Temp 1
Mult
Offset

1:14

Loc [Battery ]

8: If time is (P92)
1: 0
Minutes into a
2: 60
Minute Interval
3:10
Set Output Flag High
9: Real Time (P77)
1: 1220 Year,Day,Hour/Minute (midnight
=2400)
10: Sample (P70)
1: 1
Reps
2: 13
Loc [ LogID

]

IT. Average(P71)
1: 11
Reps
2:1
Loc [ Temp_l

]

]

3: Volt (Diff) (P2)
1: 1
Reps
2 :2
15 mV Slow Range
3 :5
DIFF Channel
4 :9
Loc [ Q16744 ]
5:320.51 Mult
6:0.0 Offset
4: Volt (Diff) (P2)
1: 1
Reps
2: 2
15 mV Slow Range
3: 6
DIFF Channel
4:10 Loc[Q 16747 ]
5:331.13 Mult
6:0.0 Offset

12: Maximum (P73)
1: 8
Reps
2: 10
Value with Hr-Min
3: 1
Loc [ Temp i ]
13: Minimum (P74)
1:8
Reps
2: 10 Value with Hr-Min
3: 1
Loc [ Temp i ]
14: Serial Out (P96)
1:30
SM192/SM716/CSM1
♦Table 2 Program
02: 0.0000 Execution Interval (seconds)
♦Table 3 Subroutines
End Program

5: Volt (Diff) (P2)
1:1
Reps
2: 2
15 mV Slow Range
3: 7
DIFF Channel
4:11 Loc [Q 1 1427 ]
5:296.74 Mult
6:0.0 Offset
6: Z=F(P30)
1:1490 F
2: 13 Z Loc [ LogID
7: Batt Voltage (P I0)

]

-Input Locations1 Temp_l 13 1
2 Temp_2 1 3 1
3 Temp_3 1 3 1
4 Temp_4 9 3 1
5 Temp_5 9 3 1
6 Temp 6 9 3 1
7 Temp_7 9 3 1
8 Temp_8 17 3 1
9 Q16744 5 1 1
10Q16747 1 1 1
11 Q11427 1 1 1

97

12 TC_ref 1 1 1
13 LogID 1 1 1
14 Battery 10 1
15
000
16
000
17
000
18
000
19
000
20
000
21
000
22
000
23
000
24
000
25
000
26
000
27
000
28
000
-Program Security0000
0000
0000
Final Storage Label File for:
WILLOWOl.CSI
Date: 4/23/2001
Time: 10:52:13
108 Output Table 60.00 Min
1 108 L
2 Year RTM L
3 Day RTM L
4 Hour_Minute_RTM L
5 LogID L
6 Temp l AVG L
7 Temp_2_AVG L
8 Temp_3_AVG L
9Temp_4_AVG L
10Temp_5_AVG L
11 Temp_6_AVG L
12 Temp_7_AVG L
13 Temp_8_AVG L
14Q16744_AVG L
15Q16747_AVG L
16Q11427_AVG L
17Temp_l_MAX L
18 Temp_l_Hr_Min_MAX L
19 Temp_2_MAX L
20 Temp_2_Hr_Min_MAX L
21 Temp_3_MAX L
22 Temp_3_Hr_Min_MAX L
23 Temp_4_MAX L

24 Temp 4_Hr_Min .MAX L
25 Temp _5_MAX L
26 Temp 5_Hr_Min MAX L
27 Temp "6_MAX L
28 Temp 6_Hr_Min MAX L
29 Temp j_ M A X L
30 Temp 7_Hr_Min MAX L
31 Temp "8_MAX L
32 Temp 8_Hr_Min MAX L
33 Temp _1_MIN L
34 Temp I H r M i n MIN L
35 Temp ’2_MIN l “
36 Temp 2_Hr_Min MIN L
37 Temp 3_MIN L~
38 Temp 3_Hr_Min MIN L
39 Temp _4_MIN L
40 Temp 4_Hr_Min MIN L
41 Temp X m in l “
42 Temp ,5_Hr_Min_ .MIN L
43 Temp 6_MIN L
44 Temp 6_Hr_Min_ MIN L
45 Temp 7_MIN L
46 Temp 7_Hr_Min_ MIN L
47 Temp 8_MIN L
48 Temp 8 Hr Min MIN L

Estimated Total Final Storage Locations used
per day 1152.0
Program Trace Information File for:
WILLOWOl.CSI
Date: 4/23/2001
Time: 10:52:13
T = Program Table Number
N = Sequential Program Instruction Location
Number
Instruction = Instruction Number and Name
Inst ExTm = Individual Instruction Execution
Time
Block ExTm = Cumulative Execution Time
for program block,
i.e., subroutine
Prog ExTm = Cumulative Total Program
Execution Time
Output
Flag High

98

Inst Block Prog
Inst Block Prog
ExTm ExTm ExTm
ExTm ExTm ExTm
TINjlnstruction
(msec) (msec)
(msec) (msec) (msec) (msec)

111117 Internal Temperature
14.0 14.0
14.0 14.0 14.0 14.0
112| 13 Thermocouple Temp (SE) 226.4
240.4 240.4 226.4 240.4 240.4
1|3|2 Volt(Difî)
74.9 315.3 315.3
74.9 315.3 315.3
74.9 390.2 390.2
1|4|2 Volt (Diff)
74.9 390.2 390.2
1|5|2 Volt (Diff)
74.9 465.1 465.1
74.9 465.1 465.1
0.3 465.4 465.4
1|6|30Z=F
0.3 465.4 465.4
7.6 473.0
1|7|10 Batt Voltage
473.0
7.6 473.0 473.0
0.3 473.3 473.3
1|8|92 If time is
0.3 473.3 473.3
Output Flag Set @ 18 for Array 108
1|9|77 Real Time
0.1 473.4
473.4
I.O 474.3 474.3
Output Data 3 Values

1|10|70 Sample
473.5
1.0 475.3 475.3
Output Data 1 Values
1|11|71 Average
479.9 35.1 510.4 510.4
Output Data 11 Values
1|12|73 Maximum
494.4 23.7 534.1 534.1
Output Data 16 Values
1|13|74 Minimum
508.9 23.7 557.8 557.8
Output Data 16 Values
1|14|96 Serial Out
510.9
2.0 559.8 559.8

0.1 473.5

6.4 479.9

14.5 494.4

14.5 508.9

2.0 510.9

Program Table 1 Execution Interval 10.000
Seconds
Table 1 Estimated Total Program Execution
Time in msec 510.9 w/Output 559.8
Table 1 Estimated Total Final Storage
Locations used per day 1152.0

Estimated Total Final Storage Locations used
per day 1152.0

D. Quantum Sensor Calibration Details
Table 1 Calibration identification
LI-190
BC Ministry o f Forests LI-1800-02.
Lamp level: 206
Calibration: Research Branch: Peter Optical Radiation □mol.m-2 s-1
(single point
November 3, Fielder (250 356-9549) Calibrator
2000
calibration)

Table 2 Sensors and calibration coefficients (mV/1000)
Sensor
Q09684
Q11427
Q10534
Q16747
Q 16744
Q16883

92/93
277.7901
323.9979
322.7347
335.8274
331.7894
359.9194

Nov. 2000
319.3552
377.269
363.2589
354.3235
355.4302
402.5359

% chng % chng/yr
13.01532 1.626915
14.1202
1.765025
11.15573 1.394466
5.220123 0.745732
6.651324 0.950189
10.58702 1.512431

LICOR lamp
:1000 □ mol.m-2
s-1

99

cal

ha

sa/
%
SN
Date code
sb LAMP dirty clned DIFF
03-Nov00
LCM 009684 SZ 206.2 1.058 1.069 1.0
03-Nov00
LCM 011427 SZ 206,2 0.885 0.9049 2.2
03-Nov00
LCM O10534 SZ 206.2 0.8987 0.9398 4.4
03-Nov00
LCM 016747 SZ 206.2 0.958 0.9635 0.6
03-Nov00
LCM 016744 SZ 206.2 0.9445 0.9605 1.7
03-Nov00
LCM 016883 SZ 206.2 0.8472 0.8481 0.1
02-Dec92
LC 009684 SZ LICOR
02-Dec92
LC 011427 SZ LICOR
02-Dec92
LC 010534 SZ LICOR
18-Jan93
LC 016747 SZ LICOR
18-Jan93
LC 016744 SZ LICOR
18-JanLC 016883 SZ LICOR
93

Calcon
St
(mA/10
00)

Cal.
Coeff
(mV/1
000)

dirty

clned

dirty

5.13

5.18

322.68 319.36 a bit variable

4.29

4.39

4.36

4.56

385.75 377.27 cable chewed
scratch
379.87 363.26
diffuser

4.65

4.67

4.58

4.66

4.11

4.11

clned

Comment

356.36 354.32 a bit variable
decreasing
signal, I.e., by
361.45 355.43
about 1%
slow to
402.96 402.54 stabilize, deer.

5.96

277.79

5.11

324.00

5.13

322.73

4.93

335.83

4.99

331.79

4.6

359.92

100

APPENDIX n
Equipment details and considerations

A. LI-1800 Portable Spectroradiometer
The portable spectroradiometer was implemented to sample light quality. Light quality
refers to how light is distributed with respect to wavelength. Some light sources, such as a laser,
have a narrow distribution while other sources, such as outdoor sunlight, have a wide distribution.
The machine measures the spectral concentration of radiant power by first dispersing the radiation
with a diffraction grating monochromater, and measures the energy in each narrow waveband of
the resulting spectrum with a silicon detector (Anonymous 1989). Output is shown in WM’^nm"'.
The LI-1800 portable spectroradiometer is a battery-operated, microprocessor-controlled
spectroradiometer for collecting o f spectroradiometric, radiometric and photometric data. The
standard optical receptor o f the LI-1800 is a PTFE-dome cosine receptor with a 180o (2m steridian)
field o f view (Anonymous 1989). Scan limits used on all measurements were 300 to 1lOOnm, with
a scan interval o f 2nm.

B. Ceptometer
The AccuPAR ceptometer was used to measure light interception in the samples at Sinclair
mills. The model PAR-80 was used and consisted o f an integrated microprocessor-drive datalogger
and probe. The probe itself contains 80 independent photodiodes, spaced 1cm apart (Anonymous
2001). The photodiodes measure PAR (Photsynthetically Active Radiation) in the 400-700nm
waveband. The units are displayed in micomols per meter spared per second (jnnolm'^®"*). The
instrument also allows output as a measure o f leaf area index, however only PAR measurements
were used in this study.
The manual PAR, full probe, point sample mode, option was used for all measurements
taken. Measurements were taken mainly on uniform, overcast. To account for variation in overcast

101

conditions, two ceptometers were used to take measurements simultaneously in the open and at the
sample tree. The results were then presented as a percentage o f full light.

C. LAI-2000 Plant Canopy Analyzer
The LAI is an estimate o f the amount o f foliage in a vegetative canopy by deducing from
the measurements how quickly radiation is attenuated as it passes through the canopy. The
attenuation is measured at several angles from the zenith, and foliage orientation information is
obtained by the instruments. Five zenith angles are measured by the machine simultaneously. The
output given is an index o f foliage, as it measures all light-blocking objects. The units o f LAI are
dimensionless, but are thought o f as; m^ foliage area/ m^ ground area (Anonymous 1992).
The assumptions that must be me for the calculations o f foliage amount and orientation to be
accurate the following assumptions should be met:
1. The foliage is black. Below-canopy readings do not include any radiation that has been
reflected or transmitted by foliage.
2. The foliage is randomly distributed. Foliage containing envelopes must be parallel tubes
such as row corps or ingle ellipsoid brush, or infinite box such as turf grass, or deciduous
forest.
3. The foliage elements are small compared to the area o f view o f each ring. The Distance of
the sensor to the nearest leaf over it should be at least four times the leaf width.
4. The foliage is azimuthally randomly oriented. The incline of the foliage does not matter as
long as all the leaves are not facing in the same compass direction. The importance o f this
assumption is reduced when a narrow view cap is used or when measurements are made in
a wide range o f directions. (Anonymous 1992). For all measurements taken with the LAI2000 plant canopy analyzer the one sensor mode was used. One reading was taken above
canopy and four below for each transmittance. A partial covering view cap was used in
bright sunlight.

102

Haiku for the weevil
The little weevil
Looked up to the spruce leader
And climbed to the top