The Growth Of Styroblock, Chemical And Mechanical Root Pruned Lodgepole Pine
Seedlings In Interior British Columbia

Dev Khurana
B.Sc. University of Northern B.C., 2001

Thesis Submitted In Partial Fulfilment Of
The Requirements For the Degree Of
Masters of Science
In
Natural Resources And Environmental Studies
(Forestry)

The University Of Northern British Columbia
April 2007

©Dev Khurana, 2007

1*1

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Canada

1. Introduction

In northern coniferous forests of British Columbia (BC) where clear cut
harvesting is commonly practiced, natural regeneration proves inadequate to meet Freeto-Grow stocking guidelines due to the unpredictably long duration of re-establishment
(Eastham and Jull, 1999). Foresters, therefore, make use of preferred species of nurserygrown containerized seedlings to re-stock cut blocks, to ensure spacing uniformity and
timely growth of preferred species (Delong et al., 1997, Wright et al., 1998).
While planted nursery stocks come in various sizes, all are, to some degree, rootbound by the containers in which they are grown (Balisky et al., 1995). Once planted,
rooting patterns have shown to be inferior from naturally germinated seedlings (Halter et
al., 1993). In an attempt to improve container deficiencies, root-pruning methods have
been recommended (Wenny et al., 1988; Winter and Low, 1990; Krasowski and Owens,
2000; Jones et al., 2002; Rune, 2003). Since the long-term success of a planted tree is
strongly determined by its ability to establish a well-developed root system (Eis, 1978),
this research has focused on evaluating the early rooting establishment in planted
lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) - BC's most commonly
planted species (B.C. MOF, 2005).
Evaluation of root development in planted seedlings needs careful attention,
which considers the tremendous efforts and costs, involved. Root growth is influenced
by three main factors: the inherent attributes of the microsite (soil and site conditions),
the nursery effect of the stock type, and planting technique. In this thesis, considering
that root development is critical to seedling establishment and growth, the hypothesis

1

being tested, is that root pruning a containerized seedling improves its rooting
development compared to the conventional non-pruned containerized Styroblock stock
(PSB). We compared various types of root pruning including several mechanically knifepruned methods (RP) as well as chemical root-pruning (PCT). Root growth parameters
were measured and analysed after 21 days from a nursery bed and after one field-growing
season on two contrasting soil conditions.

1.1. Objectives
The primary objective of the thesis was to compare one-year growth parameters of
lodgepole pine seedlings planted as conventional Styroblock stock type (PSB) with
conventional chemical treatment (PCT) and several mechanical (or knife) root pruning
(RP) treatments. The response of seedlings to different pruning treatments was assessed
in two contrasting site conditions at Red Rock and Aleza Lake sites.

2

2. Review of Literature

2.1. Reforestation and the Artificial Plantation
The trend in scale of reforestation has dropped over the recent years from 253
million seedlings planted in the 1994-95 period (Barlette, 1996), 232 million in the 199798 period, to 170 million in the 2004-05 period (BC MOF, 1996). However, it may again
be on the rise with the increases in rate of harvest as a result of salvaging from the pine
bark beetle epidemic. In the 2005-2006 year period, 197,600 ha were cut.

While

harvesting method has remained stable at about 90% clear-cutting over the last decade
(the remainder being selection harvest systems), the size of the cuts has dropped since the
late 1980's from an average of 45.5 ha to 26.6 ha (Barlette, 1996; Gov. of BC, 2000).
With objectives of sustainability, reforestation standards exist as Free-to-Grow
stocking guidelines to ensure that harvested areas meet density targets for regeneration,
with a minimum height requirement within a set timeline and be relatively free of
vegetative competition.

Foresters comply with the Free-To-Grow

legislation

requirements after clear-cutting using artificially planted nursery stock. This provides the
greatest management control of regeneration at predictable densities of preferred species
in a timely fashion.

Once a plantation meets the standards of Free-To-Grow by

successfully reaching its growth requirements, foresters are removed of any further
liability securing a fixed allowable cut without penalties from non-sufficiently stocked
back-log of previously harvested areas. Thus legislation and economics has created a
ubiquitous management strategy in BC that has streamlined forests for clear-cut
harvesting methods with artificially planted regeneration.

3

In order to ensure plantation success, foresters manage with broad based
silviculture treatments at the resolution of the site unit that are several hectares in scale.
Some of the generalized silviculture activities that are carried out on these site units
include: site preparation, chemical brushing and herbicide, manual brushing, fertilization,
pruning and spacing (BC MOF, 2005). The cost of reforestation is a big driver for the
BC economy.

A yearly cost of $150 million is spent in efforts to cover costs of

reforestation (Gov. of BC, 1990).
Relying on natural regeneration with clear-cutting as a harvesting method poses a
risk in achieving regeneration guidelines. Natural regeneration is arguably unreliable
because of a limited availability in seed-bed substrates mostly the result of winter
harvesting. Also, there has been a great reduction in the use of prescribed fires (Barlette,
1996). Additionally clear-cutting methods reduce the availability of seed of preferred
species (Eastham and Jull, 1999).
Over the last quarter century, the BC landscape has seen an alteration of a great
portion of our mature forest into a mosaic of disturbance patches of uniform size, shape,
height, and species. In this way BC forest resources are scheduled to achieve sustainable
timber as forecasted in the Timber Supply Analysis (B.C. MOF, 1996). Certainly the
current regeneration regulations are hardly ecologically based. Uniformity of even
density plantations does not mimic the natural regenerating progression of disturbed
stands nor do they mimic any natural disturbance type.

As such there is minimal

variation to the reforestation management strategy regardless of the forest ecosystem or
disturbance regime (BC MOF, 1998).

Of the 183 million seedlings planted in the

2005/06 period, most commonly planted species were 9% Douglas fir {Pseudotsuga

4

menziesii var glauca), 30% hybrid spruce (Picea glauca Voss. x engelmanii Perry) and
48% lodgepole pine. (Pinus contorta Dougl. var. latifolia Engelm.) (BC MOF, 2005).
About, 96%) of the seedlings planted are of containerized stock type, the remaining 4%
being that of a bareroot type (BC MOF, 1998).

2.2. Natural Seedling Root Development
Roots act to anchor and support the tree, for storage of energy reserves such as
carbohydrate, and an instrument to sequester available soil water and nutrients
(Kozlowski, 1997). Initially root development is influenced by genetic control and by
environmental conditions in which the seedling is grown (Horton, 1958; Eis, 1978).
Genetics control the radical (primordial root) to develop from the germinated seed. This
primordial root establishes vertically as cells divide longitudinally in the root cap. The
root penetrates downward and a tap-root is developed. The first branches are primary
lateral roots that emerge progressively down the tap from the root collar at the soil
surface. Like the tap-root, primary lateral roots develop with rapid rates of growth and
longer durations of meristematic activity (Puhe, 2003). Primary lateral roots structurally
anchor the tree to the soil and serve as conduits of nutrient transfer from finer 'feeding'
roots proliferating extensively in the soil environment. Secondary roots may also emerge
from the tap and primary laterals. These are smaller in diameter than primary roots and
non-structural.
As roots enlarge with growth rings, termed secondary growth, the pattern of the
structural root system becomes established. Root growth is described as compensatory,
that is, roots grow rates differ according to soil condition (Kozlowski, 1997; Krasowski et

5

al., 1999). For example, enhanced root growth is commonly found in areas where soil
structure, temperature, bulk density, root penetration, nutrients, and moisture provide a
favourable environment for growth (Sutton, 1980).

However, the development

mechanisms of a natural mature root system have yet to be fully understood. Main
structural roots of a root system likely develop in the early stages of tree development
(Martisson, 1986); yet, trees have the capacity to change over its lifetime with death and
replacement (Preston, 1942). In northern forests of central BC where soils are cool and
humid, root development is more intensified near the soil surface. This includes roots of
all sizes ranging from structural roots to small mycorrhizal feeder roots (Preston, 1942;
Heineman et al., 1999; Puhe, 2003). Surface soils tend to be warmer, more aerobic, less
dense, and more enriched with nutrients than sub-surface horizons (Eis, 1978).
Essentially, the root system grows expansively as well as prolifically to encompass
sufficient soil volumes to endure the variability of climate as well as out-compete others
within the stand. In all species, root systems of dominant trees have consistently betterdeveloped root systems with more branches, more symmetry and greater root to shoot
ratio than root systems of other trees (Eis, 1978).
Among species, root morphology varies due to genetic differences.

Within a

species, root systems vary mostly due to soil environmental conditions giving rise to
characteristic root systems that are predisposed to a certain range of soil conditions (Eis,
1978; Strong and Roi, 1983). Rooting development strategy varies across a large range
of soil edaphic conditions as in the case for lodgepole pine (Pinus contorta Dough var.
latifolia Engelm.)

In well-drained soil conditions, lodgepole pine is often tap-rooted

usually displaying a whorl containing 3 to 11 primary lateral roots (Eis, 1978; Horton,

6

1958). Alternatively, but less frequently, a heart root system develops in the absence of a
taproot, where primary roots develops sinkers roots oriented vertically to form a
characteristic heart shape root system (Fig. 2.1). In poorly drained and compact soils, a
supporting tap root system is abandoned for a shallow spreading root plate system
(Horton, 1958; USDA, 1990). Strong and Roi (1983), in their study of root development
of Jack pine in boreal environments, observed the ratio of biomass allocation of lateral
structural roots to vertical tap roots to be 0.60 and 0.95 for well and poorly drained sites,
respectively. The behaviour of natural rooting systems has been well studied and serves
as the standard to which planting stock types are compared (Halter et al., 1993, Preisig et
al., 1979).

TAP

sySTEiA

J J ^ T fufiVc.

<L©<3T 5Y*T ) er^

M£*£T

Figure 2.1. Characteristic forms of root systems in northern conifer species.

7

2.3 Achieving a Quality Planted Seedling
Nursery-grown seedlings must remain vigorous through the process of
transportation, handling and planting in order to achieve high success of survival.
Nursery production of seedling root systems must be free from deformities to allow the
development of primary coarse structural roots characteristic of its species. Planting
method must avoid developmental deformities.

While the plug must remain snug,

planting method should not compact the soil or rooted plug either vertically or
horizontally. Primary lateral roots must be able to develop symmetrically to capitalize on
available soil volumes and maintain the stems stability.
To increase survival rate of planted seedlings, forest management activities
should not impede the existing productive capacity of the site. To provide optimum
growth, harvesting practices and site preparation treatments should avoid degrading the
productive capacity of site. For economic and commercial reasons, a planted tree should
be established with low economic investment and should exist with minimum impact to
the ecology of natural forest system. A planted tree should not replace existing healthy
preferred or acceptable naturally regenerated seedlings. Reduction of existing healthy
preferred residual trees with harvesting and site preparation should be avoided.

2.4 Evolution of the planted seedling: the Styroblock - PSB.
Early tree plantations were reforested with bareroot stock that were established in
nursery beds and with roots mechanically pruned to restrict the extent of root growth in
favour of a bushier root system. After one or to two years in field beds at the nursery,
bareroot stocks were excavated, packaged into boxes, and transported to the site for

8

plantation. With mechanization in the late 1970's, seedlings switched to being grown in
green houses on trays of varying sized seedling containers filled with peat and
vermiculite.

Container grown seedlings achieve greater economic efficiency, with

greater product reliability in increased quantities with little differences to growth
performances of bareroot stocks (Becker et al., 1987; Burdette et al., 1984).
Today, in BC and in the rest of Canada, seedlings are almost universally container
grown (Barlette, 1996) and are commonly referred to as Styroblock seedlings. Their
rooting pattern has been well characterized by Balisky et al. (1995). Plug Styrofoam
Block (PSB) seedling is grown in styrofoam trays with ribbed dimensional cavities. The
cost of PSB seedlings varies with size of the growth cavity or the number of seedlings in
a given tray. The walls of the container limit and bind root development in the cavity
over their first growing season. Vertical ribs were introduced to the containers to reduce
the incidence of root spiral, a deformity caused when primary lateral root preferentially
grow horizontally in intertwining spirals around the container. With ribbed cavities, roots
typically deflect downward along the walls of the plug and coalesce at the bottom where
they are air pruned at the cavity water drain hole. When lifted from the tray cavity,
containerized seedlings are easily handled with its rooted plug neatly amassed and
intertwined with branching roots that coalesce at the bottom of the plug.
Salonius et al. (2000) found a rather weak correlation (R = 0.50) between initial
root density (mg root/ container volume cm3) in the plug and root growth in a one-year
field trial for black spruce. Height growth showed a negative relationship to initial root
density (R2= -0.46) perhaps due to root bind. Initial plug root density was correlated
(R2= 0.90) to its soil to space ratio (the seedling container volume relative to the density

9

per tray). Thus, reduced root bind within the plug as a result of growing seedlings at
higher densities can explain almost half of the increased root growth after one year of
planting in the field. When planted, seedlings with the lesser-developed root systems
grew proportionately more and consequently explored more initial soil volume than
seedlings with well-developed root systems. Providing stem height and vigour can be
maintained, a threshold of crowding of nursery seedling is considered beneficial to their
field rooting performance.
Initial root biomass of containerized seedlings did not reflect the function of root
growth in a water conductivity experiment by Krasowski and Caputa (2005). Individuals
with increased initial root biomass for a given containerized plug volume neither reliably
explained the ability of roots to absorb nor to conduct water.

Such evidence helps

support the theory that excessive root density plug and associated root bind can reduce
the ability of a seedling to maximize its root development when planted in the field.
Results presented at the Symposium on the Root Form of Planted Trees (Van
Eerden, 1978) demonstrated that both nursery and planting techniques causes a certain
degree of root deformation. The potential for root deformation is species specific. The
pine genus has been identified as species more prone to deformation (Van Eerden, 1978;
Halter et al. 1993). Containerized PSB roots have been demonstrated to restrict lateral
development and radial symmetry due to their initial confinement within the container.
Once planted, root egress occurs mostly from a portion of the coalesced roots at the
bottom of the plug often in one or two directions (Wenny et al., 1988; Heineman, 1991;
Balisky and Burton, 1997; Krasowski and Owens, 2000). Van Eerden (1978) observed
that the restriction of lateral root development was higher in lodgepole pine than hybrid

10

spruce or Douglas fir, and that trajectory of its root egress was in the direction of their
initial orientation.

In later research, Van Eerden (1981) argues that deformed root

systems of planted trees can overcome their initial deficiencies and eventually acquire a
more normal rooting habit. In the long term, it is possible that the root architecture of a
planted seedling may develop adventitiously from the stem (Coutts et al., 1990).
However, this phenomenon is species specific, and is strongly observed in certain genera
like spruce but not pine.
Indeed the root growth and form of nursery seedlings remain markedly different
than those that geminated naturally. Fig. 2.2 demonstrates growth differences between
planted and natural stock with the structural roots of the planted tree is different in
number, size, and location. Robert (2004) showed comprehensive differences in root
morphology between planted juvenile lodgepole pine and naturals. Planted stock showed
much greater root deformities than natural germinates. Some roots have the ability to
graft to reduce abnormalities such as tangling (Van Eerden, 1981; Halter et al., 1993,
Wass and Smith, 1994).

Severe root deformities have been shown to impede the

translocation of sugars through the phloem (the inner bark) exhibiting growth
exaggerations above the constriction described as root balling (Hay and Woods, 1978).

11

Figure 2.2. Comparison of excavated 3-year old pine seedling near 70 Mile House. Left,
natural germinant; Right, PSB 3-13 seedling showing dead needles from previous year's
growth due to stresses imposed during establishment.
In favourable microsites, roots of planted trees emerged from the plug in
abundance of 50 - 120 roots (Balisky and Burton, 1997). As trees mature, the numbers
reduce to 3-10 dominant structural roots (Eis, 1978). Root deformities, caused by
abnormal root growth in the container, create impediments and restrictions to growth.
Deformities are described as kinks (abrupt changes in direction) and braids (root
strangulation causing constrictions in growth of vascular and cork cambium growth).
Fig. 2.3, below, shows two cases of 6-year-old pine. The left shows stem curvature and
bilateral root symmetry, likely the result of the shovel blade compacting soils in two
12

planes at the time of planting. The right shows a compacted plug as a result of improper
planting technique. Note the lack of structural primary roots and also the diameter
difference between structural primary roots and secondary roots.

Figure 2.3. Six-year-old Pine seedlings showing poor rooting development - 70 Mile
House.

For most studies, observations are limited to short term growth indices such as
survival and height growth. Height measurements do not allow for the evaluation of subsoil root development that may ultimately affect long-term development of the seedling.
Reduced numbers of large primary roots, reduced root symmetry, and root deformation
may lead to stem deformities such as curvature (eventually leading to compression wood
undermining wood quality) (Krasowski, 2003). Studying long-term growth may also
address seedling resilience to unfavourable environmental conditions such as stochastic
events of wind, snow, and drought.

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2.5. Root Pruning as an Alternative
Seedlings are grown in Styroblock (PSB) because of cost efficiency and high
success rates of tree establishment. Many advances in handling and processing PSB
stocks include several alternatives such as root pruning techniques. Current forms of root
pruning include air holes through the sides of the container called air pruned blocks
(Rune, 2003), mechanical (knife) pruning as in Vapo technology (Krasowski and Owens,
2000) and chemical root pruning (PCT) where copper oxychloride is painted on the wall
of the Styroblock (Jones et al., 2002). The principal aim of root pruning treatment is to
retard the growth of lateral primary roots as they approach the walls of the container.
This avoids forcing root growth in a downward trajectory and subsequently avoids having
roots entangle with each other. Unfortunately, root pruned stocks are less commonly
used due to various limitations and lack of short-term enhancement of height growth
performance.

With air-block stock, growing trays are costly and require high

maintenance because of susceptibility to drought and in many cases show higher rates of
nursery mortality. PCT stock has slightly higher costs due to the tray's shorter life span
and disposal issues associated with the toxic metal paint (Jones et al., 2002).
Results from many studies on the performance of various types of seedlings,
showed varied growth improvements. Often measured in the short term, the implications
of root pruning are hard to evaluate. Evidence from Burdette et al. (1983), Wenny et al.,
(1988), Krasowski (2003), Krasowski and Owens (2000), Jones et al. (2002) and Rune
(2003) suggest that root pruning increases root development in the upper portions of the
rooted plug but the effect of root pruning is not conclusive with respect to height growth
or survival. Burdette et al. (1983) reported that when an applied chemical paint was

14

added to the wall of the lodgepole pine container as compared with the non-pruned
control, height growth increased in the 4-year measurements.
With mechanical root pruning, a nursery practice used to localize root growth in
bare root seedlings, seedlings exhibited adventitiously budded root primordia within the
vascular cambium as a physiological response to injuries sustained during pruning
(Sutton, 1980). Box pruning, a systematic mechanical root pruning method where roots
are repeatedly pruned to reduce the space constriction in a containerized plug, produces a
burst of increased growth despite initial low root to shoot ratios for both pine and spruce
species (Krasowski and Owen, 2000; Krasowski, 2003). Once knife pruned, cut primary
lateral roots develop new large diameter tips. Experiments with repeated mechanical
pruning systems such as box pruning showed high total water flux (Krasowski and
Owens, 2000), less crooked stems (Krasowski, 2003), and larger initial starch reserves
(Edgren, 1975). However, the high cost of repeated mechanical pruning prohibits its
general use in the forest industry.

A single root pruning of PSB stock may be a

compromise to achieve a similar effect.
Presently, a discrepancy exists in the prescribed use of stock types for pine
reforestation between licensee tenured blocks and by the BC Timber Sales (BCTS)
blocks. Licensees favour PSB stock while BCTS prefers the PCT stock types due to the
improvements in root morphology (Bob Merrell, MOF administrator for coastal
nurseries, and Mike Theliz, Manager of PRT Nursery, Red Rock, personal
communication).

Well-developed root system in the long-term may correlate with

juvenile height growth, and fits with the vision of sustainable forest management. The
law, if not the licensee, must promote long-term benefits of a planted tree.

15

2.6. Rationale for Knife Pruning
Many root-pruning studies were developed to improve the cultural practice of
reforestation using bare root seedlings.

Blake (1983) found a lack of physiologic

responses to root pruning treatments of 0, 25, 50 and 75% removal of the initial root
volume. No differences either in transpiration rates, drought resistance, or stomatal
resistance could be detected between pruned and non-pruned seedlings after a 6-week
period for planted white spruce. Paterson and Maki (1994) examined the effects after a
six-year field performance trial on Jack pine between bare root and root-pruned seedlings
(25, 50 and 75% removal) on disk trenched sandy loam in Ontario. After the first year,
survival was greatly reduced to 60% in the 75% pruning treatment as compared to 8387% survival in the other treatments. Of those who survived, heights of seedlings in the
control treatment were 10 - 13 cm taller than seedling heights in 50 and 75% pruning
treatments.
With PSB stock, Bigras (1998) showed that after a two-year trial on black spruce,
0, 20, 40 60 and 80% root removal treatments did not show significant difference in
seedling survival. Growth index such as height showed 3% gain with 20% removal and
declined by 1, 3 and 13% in the 40, 60 and 80% pruning treatments, respectively.
Diameter growth showed a negative trend throughout the treatment regime with 1, 4, 8,
and 19% reductions in diameter, respectively for the 0, 20, 40 60 and 80% treatments.
In a two-year study on bare root beech (Fagus sylvatica L.), Anderson (2001)
compared root growth after coarse roots (> 2 mm) and fine root (< 2 mm) removal in
addition to root cuts at 7, 13, and 19 cm to the 25 cm-long control seedlings. Anderson

16

(2001) reported that beech trees were sensitive to the loss of roots irrespective of
environmental conditions.

Mortality was high with treatment of > 50% removal,

regardless of applied irrigation. Also evident was top shoot die back with root pruning.
Fine root removal treatment showed pronounced declines in growth and survival
regardless of site condition. Fine roots, it seems, are of greater immediate necessity to
establishment than large roots. Personal observations by the author have shown that of
the transplanted wildlings (natural geminated seedlings) for horticultural purposes, pine
species and deciduous trees such as birch and aspen are of greater sensitivity to root
pruning as compared with other conifers like spruce and Douglas fir.
Winter and Low (1990) compared PCT, mechanically pruned and uncut PSB 3-13
stocks of lodgepole pine in interior BC. Mechanical pruning (MP) treatments removed 1,
3 and 5 cm from the bottom of the plug. After 5 years, the 3 cm cut showed small height
growth improvements; where as, height growth and survival was reduced in the 5-cm
removal treatment. No differences were observed in height with the PCT treatment. In
all pruning treatments, mechanical and chemical, root growth symmetry was greatly
improved in radial direction of primary roots. After 5 years, PSB seedlings were mostly
bilaterally symmetric. Root balling, the result of root deformity and subsequent swelling,
showed greatest reduction in PCT stock but was unaffected in MP treatments.
The aforementioned experiments suggest that root-pruning of coniferous
seedlings slightly improves the growth of trees up to a certain point and then likely
reduces growth and survival beyond that. The studies also suggest that rooted plug can
tolerate a considerable amount of root pruning to correct the larger root deformities and
allow for their proliferation into greater soil volumes.

17

A series of cuts to the rooted plug may stimulate root growth in a variety of ways:
promote adventitious primary roots to develop in the buried stem, support greater surface
lateral development, reduce root entanglement, promote greater radial symmetry and
engage greater initial soil volumes. Since soil conditions vary, a pruning regime may be
found that would benefit seedling root development specifically for certain soil types.
Regardless of method, two assumptions must be made: first, knife pruning must be blind
to the specific locations of roots within the plug in order to keep it operational, and
second, root pruning must be facilitated in manner that rooted plugs can be handled such
that it can be planted without falling apart.

2.7. Effect of Microsite on Seedling Development
Site preparation techniques such as mounding, trenching, prescribed burning, and
herbicide treatments have been reported to improve the growth and survival of planted
seedlings (Jones et al., 2002; Heineman et al., 1999; Bednesti FRDA II, 1992; Patterson
and Maki, 1994).

An alternative to site preparation, which is being increasingly

practiced, is duff or straight planting where seedlings are directly planted into the forest
floor horizons. This method has proven to be favourable to seedling growth under certain
soil and vegetative conditions (Heineman, 1998; Balisky and Burton, 1997).

Duff

planting minimizes site preparation costs and reduces risk of soil compaction associated
with heavy machinery.

Unlike site prepared ground, duff planting necessitates the

planting of cut block soon after harvesting while competing vegetation is at a minimum.
Duff planting necessitates that the tree planter be more aware of specific planting

18

requirements like microsite, species, and spacing selection as well as the identification
natural tree seedlings.
While stock type has shown relatively minor effects on growth and survival,
variations in soil environmental conditions strongly influence the development of planted
seedlings (Balisky and Burton, 1997; Jones et al., 2002). Root growth morphology is
strongly altered by the conditions in which the tree grows as seen in Fig. 2.4. While
growth rate and pattern of root development are species specific (Eis, 1978), growth
parameters are also dependent on the microsite conditions, including soil and
environment (Eis, 1970; Heinemann, 1991; Delong et al., 1997). Patterson and Maki
(1994) suggested that the selection of an appropriate microsite has greater influence on
growth than planting method in Jack pine seedlings grown in a trenched sandy soil. Wass
and Smith (1994) demonstrated that 59 % of 6-year old Douglas fir seedlings had roots
conforming to the shape of the planting shovel while areas with compacted soils showed
obvious root restrictions in vertical development. Delong et al. (1997) found that
decomposed logs, mounds and exposed mineral substrates in boreal Alberta were better
for establishment than shovel screefs and undisturbed humus (surface organic) seedbeds.
Heineman (1991), in a study of planting method for two-year old PSB 4-15
interior spruce stock on a cool hygric site with thick forest floors, found differences in the
form of root systems across microsite treatments but failed to show height growth
differences among treatments after two years. Trees grown in woody substrates had
fewer roots but these were elongate and shallow with few branches. Microsites that were
very wet or imperfectly drained, particularly found in screefed mineral spots had few
roots egress out of the bottom of the plug favouring only surface roots showing any sign

19

of coarse root differentiation. Where mineral soils were better draining, root egress was
described as bushy, with abundant branching and steeply ascending roots.

The

development of seedlings planted into the 20-cm thick F and H organic horizon was
intermediate between the well-drain mineral soil and the wood microsite types.
Narukawa and Yamamoto (2003) demonstrated the adaptability of roots in Abies seedling
that were naturally germinated and stratified by soil type to decayed wood and mineral
forest floor substrates. Strong patterns in rooting morphology were observed in the
different substrates. Egress of planted seedling roots that are adaptable to soil condition
is seen as desirable to the quality of plant tree species as they will likely have greater
survival, be more tolerant of stresses, and show better stem form.

Figure 2.4. Excavated planted spruce seedlings on the same cut block from Aleza Lake
after one growing season from different microsites: well draining sand, poorly draining
clay, wet but well draining woody debris.

20

Van Den Driessche (1987) showed that new root growth of transplanted seedlings
is primarily composed of photosynthate since time of planting. If light is inadequate,
some reserves may be utilized but the amount of new growth appears dependent on
photosynthesis.

Root morphogenesis is determined by soil properties such as bulk

density, pore size and distribution, soil strength, moisture content, oxygen availability,
temperature, fertility, acid toxicity, reaction, and soil depth (Sutton, 1980). Growth of
shoot relative to root decreases with declining amounts of available water, nutrients,
oxygen and temperature (Fitter and Hay, 1987).
In cool northern forests where moisture is not limited, microsites with higher
average daily temperatures produce seedlings with lower shoot to root ratios (Heineman,
1991). In a one-year pine trial on high elevation forests in interior BC, Balisky and
Burton (1997) observed that cool microsites (10-13 °C) resulted in decreased root counts
and reduced stem heights as compared to warmer sites (18-25 °C). PSB stock had poor
lateral performance characterized by the dominant root egress at the bottom of the plug
regardless of microsite types. Furthermore, in colder ecosystems it was suggested that
bottom root development, typical of the PSB seedling, was a handicap, since root growth
is directed into the colder soil horizons where they likely increase their susceptibility to
over-winter injury (Krasowski et al., 1996). In a hydroponics study (Vapavuori et al.,
1992), low root temperatures (5 and 8 °C) decreased or inhibited the initiation and
elongation of European Norway spruce and Scots pine roots.
During waterlogged periods, higher proportion of fine root biomass of grand fir
was more dead than alive despite its greater tolerance than Norway spruce to anoxic
conditions at greater vertical depth (Xu et al., 1997). Under dry soil conditions, root

21

systems of young Scots pine and Norway spruce ceased to grow at moisture content
lower than -1.5 MPa. However, root growth resumed and even increased within 6 days
of re-wetting. Root elongation was higher in lateral direction than vertical orientations
with rates equivalent to 4.8 and 12.3 mm per day for spruce and pine, respectively
(Bartsh, 1987).
With a better understanding of the effects of microsite conditions on seedling
establishment and tree root growth, foresters can make more effective harvest
prescriptions and site preparation techniques. In addition, tree planters can make better
selection of microsites and implement appropriate planting techniques to ensure high
rates of seedling survival and development. With respect to root pruning, microsite or
soil type will likely show growth interactions supporting greater results from the
treatment in distinct soil conditions. Because root pruning reduces root densities, it may
be seen as detrimental on the drier sites. But as root pruning alters the distribution of
roots with greater distribution of roots through the plug, greater improvements in root
development may be realized in soils that are wetter and colder in condition.

22

3. Experimental Methods
3.1 Site Descriptions
3.1.1 Red Rock
The Red Rock site is located at PRT nursery field beds (53°45'48" N,
122°42'05" W) roughly 30 km south of Prince George. Perched on a terrace 58
meters above the Fraser River at an elevation ~ 617 masl (Table 3.1), site topography
is uniformly flat. Soils were derived from a bed of periglacial deltaic sand bed that
sits with conformity above clayey glaciolacustrine sediments (Tipper, 1971).
Pedogenesis was dominated by anthropogenic influence from repeated ploughing, and
resulted to a well-developed 35-cm thick plough layer (Ap) (Fig. 3.1).
Soil profiles at Red Rock were divided into three strata: Upper (0-10cm), Middle
(10-20cm) and Lower (20-3 0cm), for the characterization of soil properties. Bulk density
(Db) was determined using undisturbed core method (Blake and Hartage, 1986). A
sample core volume of 491 cm3 (9.7 cm diameter and 6.65 cm long depth) was used.
Bulk densities in 6 randomly positioned replicates ranged from 1.53 to 1.64 g/cm3 in
Upper, 1.35 to 1.48 g/cm3 in the Middle, and 1.55 to 1.68 g/cm3 in the Lower strata
(Appendix A). Being a ploughed site, the Upper and Lower strata have significantly
higher Db than the Middle stratum. Drainage is rapid at the Red Rock site due to its
sandy texture. The site has submesic moisture regime based on ecosystem site description
guidelines (Gov. of B.C., 1988). Submesic soil class has soil water content regulated by
precipitation rather than seepage.

Moist for only brief periods of time following

precipitation, water percolation is rapid in relation to its supply. Aeration was confirmed
up to a depth of 75 cm based on three soil pits across the site in the wet October period.

23

Soil at 15 cm depth was uniform across the entire site as single grain structure and loose
consistence.

Figure 3.1. Red Rock soil profile to a depth of 60cm has sandy texture, strong
granular structure, and loose consistence; a ploughed horizon (Ap) is evident from
surface to the middle of the picture.
Climate at Red Rock, based on records from a Prince George weather station
(STP, data 1971-2000: 579 masl, located 13 km to the north on the west bank of the
Fraser River) is relatively mild and dry. Mean annual temperature is around 5 °C
with a mean annual precipitation of 550 mm. Spring months of March and April have
the least mean monthly precipitation of 26 mm and 30 mm, respectively.

Mid

summers months of June and July receive the highest mean monthly precipitation at
53 mm and 56 mm, respectively. The growing season from May to September
receives an average of 260 mm of precipitation and 14.5 °C mean temperature.

24

3.1.2 AlezaLake
The Aleza lake site is located at the Aleza Lake Research Forest (54°01'57"N,
122°08'52" W) at km 47.5 on the Bear Forest Service Road ~ 40 km east of Prince
George. The cut block sits at ~ 710 masl. The surrounding terrain is flat, punctuated with
sphagnum bogs and the occasional dissected creek. Aleza Lake parent material consists
of a thick glaciolacustrine mantle of sediments originating from periglacial lake Prince
George developed at the time of deglaciation of the Cordilleran ice cap. Within the subaqueous kame deltaic environment, minor topographic relief reveals a mosaic of soil
textures from well drained sands to poorly drained clay (Tipper, 1971).
Within the experimental area of the Aleza Lake site, textures ranged from silt
loam to clay. Typical of forest soils, bulk density (Db) at the Aleza Lake site increased
with soil depth within the 30 cm soil profile (n=15) and ranged from 0.36 to 0.87 g/cm3 in
the Upper (0-10cm), 0.97 to 1.27 g/cm3 in the Middle (10-20cm), and 1.00 to 1.47 g/cm3
in the Lower (20-30cm) strata (Appendix A). Aeration depth measurements using the
iron rod method (Carnell and Anderson, 1986) revealed that median summer aeration
depth was 39.5 cm (n=12) in August 2005 (Appendix B). Fall rains reduced median
aeration depth to 26.5 cm (n= 106) (Appendix C). Thickness of forest floors at Aleza
Lake ranged from 1 to 12 cm with mean value of 5.3 cm (SD = 2.2 cm, n=101)
(Appendix C). Thicker forest floors measured at the Aleza Lake site were associated
with decayed wood materials and upturned root wads where topsoil accumulated in
discrete volumes. The Aleza Lake soil typically demonstrated a mull humus form with a
characteristic Ah horizon (Greens et al., 1993).
prevalent.

25

Earthworms were evident but not

Based on site aeration and moisture content, soil moisture regime at the Aleza
Lake site ranged from hygric to subhydric (Gov. of BC, 1988). Puddles were evident
with heavy fall precipitation within the recently logged area.

Anaerobic soil

conditions associated with poor water infiltration produced mottles in the mineral soil
(Fig. 3.2). Permanently saturated soils were observed on microsites exhibiting gley
soil conditions. Additional description of physical and chemical characteristics of
soils at Aleza Lake can be found in Arocena and Sanborn (1999).

Figure 3.2. Aleza Lake soil profile characterized by hygric moisture
regime, fine textures, shallow rooting, mull humus form (Ah) and mottled
horizons (Luvisolic Btg) (mottles not visible on photo).

Soil structure was described at the 15 cm depth from excavated cores, showing
various characteristics ranging from massive structure with a characteristic anaerobic
sulphurous smell; weakly developed blocky structure with gleying within peds and
mottlings on the ped surface (Fig. 3.3); granular structure and friable consistence with

26

clay enrichment and mottling at depth (Fig. 3.4), and granular structure and loose
consistency with mottling (Fig. 3.5).

Figure 3.3. An example of soil at Aleza Lake site with mottled, large,
weak sub-angular blocky structure and firm consistency (mottles not
visible on photo).

.•judT'

2' Jn- ~_

Figure 3.4. An example of soil at Aleza Lake site with moderate to
strong, granular and friable consistency.

27

Figure 3.5. An example of soil at Aleza Lake site with strong granular
structure and loose consistency.

Vegetation at the Aleza Lake site showed considerable variety. Hybrid spruce
(Picea glauca x engelmannii), subalpine fir {Abies lasiocarpa) and paper birch
(Betula papyrifera) existed throughout the study area while isolated Douglas fir
{Pseuotsuga menziesii var. glauca) dominated the canopy where site drainage was
rapid. Western hemlock {Tsuga heterophylla), commonly found in the eastern part of
the Rocky Mountain trench were infrequently scattered, black spruce {Picea mariana)
and lodgepole pine {Pinus contorta var laifolia) graded into the forest community in
the clayey and wet areas.

Devils club (Oplopanax horridus), raspberry (Rubus

idaeus), lady fern {Athyrium filix-femina) and red stem moss (Pleurozium schreberi)
dominated the zonal sub-canopy while rushes {Juncaceae), coltsfoot {Pedasites sp.)
and sphagnum moss {Sphagnum sp.) were found in the wetter areas.
The biogeoclimatic zone for Aleza Lake is Wet Cool Sub-Boreal Spruce (SBS
wkl) characterized by relatively severe and snowy winters with short, cool and moist

28

growing seasons. Mean annual precipitation is high for the sub boreal plateau at 930 mm
with 374 falling as snow; snow packs average ~ 1 m. The growing season from May to
September averages 336 mm of precipitation. The mean annual temperature is ~ 3 °C but
recently this average is closer to 4 °C as recorded froml941-1970 and from 1998-2003 at
the Aleza Lake Weather Station.
A feller-buncher and grapple skidder harvested the cut block in the winter of
2003/2004. Typical of contemporary harvesting systems, a modest retention of nonutilizable species was retained.

Slash, treetops, branches, and discards of non-

merchantable logs were piled and burned. The block was left fallow for a year after
harvest and planted in the following May 2005.

3.1.3 Site Summary
Table 3.1 Selected site characteristics of the study areas
Site Characteristic

Red Rock

Aleza Lake

Elevation (masl)
Annual Precipitation (mm)
Texture
Drainage
Moisture Regime (0-8)
Median Aeration Depth

617

710

550

930

Sand

Silt Loam to Clay

Rapidly well

Poor

Submesic (3)

Hygric to Subhydric (6-7)

Greater than 75 cm

Summer: 39.5cm / Fall:
26.5cm
Mull 5.3 ± 2.2cm

Forest Floor
Soil Structure and
Consistency

None (Ap layer)
Single Grain, Loose

Granular to Blocky,
Friable to Hard

3.2. Site Soil Moisture Characteristics
Seasonal fluctuations of moisture content were determined with intermittent
sampling. Due to the constraints of access to the Aleza Lake site, measurements were

29

limited to three sampling times. Moisture was calculated from a composite of 16
samples collected using core method (Gardner, 1986). A 2 cm x 30 cm soil core was
inserted into ground at designated site markers to capture site uniformity with
successive measurements. Soil samples were divided into the Upper (0-10cm) and
Lower (20-30cm) strata of the collected cores. Soils were weighed initially then reweighed oven dried at 100 °C. Moisture content (MC) of a given soil stratum was
derived as:
MC (%) = ((mass wet soil - mass dry soil) / mass dry soil) * 100

(1)

Volumetric moisture allows comparison across soils of different bulk density and was
calculated as:
Vol. MC (%) = MC (%) * Mean Stratum Bulk Density

(2)

A one-time fall profile volumetric moisture determination was done to
determine site variability within the 30-cm moisture profile. Here, the entire 30-cm
core was collected within 5 cm of trees selected for excavation. Profile Volumetric
Moisture was determined by calculating the MC (%) as described above, in seasonal
moisture, multiplied by the site average profile bulk density (Appendix A).

3.3 Stock Types
This study used genetically improved class 'A' lodgepole pine seed (lot
number 60297). Operationally, the seed-lot is suited for elevation range between 700
to 1200 meters covering a wide range of the interior of British Columbia (from the
Kootenay region to Smithers). The following stocks were provided by PRT and
Peltons Nursery for use in the study: PSB 4-15b, 2 boxes - 540 seedlings; PCT 4-10,

30

1 box - 270 seedlings; PCT 5-12, 1 box - 105 seedlings. Seedling stocks are coded as
follows: PCT - Plug Chemically Treated conventional containerized stock, and PSB Plug StyroBlock, the conventional non-treated Styrofoam container stock (Table 3.2).
The numbers associated with stock type refer to the ~ dimensions of the seedling root
cavity (e.g., 4-10 = 4cm diameter and 10 cm long plug). Due to the limited supply of
the seedlot at the time of the experiment, two sizes of PCT stock, 5-12 and 4-10, were
used to compare against PSB 4-15 control (Fig. 3.6).

PCT 5-12

PCT 4-10

PSB 4-15

Figure 3.6. Root and shoot differences in the stock types used in the study.
Some of the initial differences include the following: size differences in root
and shoot.

31

Table 3.2 Stock dimensions (n=45) and growing conditions (B.C. Ministry of Forests,
1998) and estimated cost per tree (PRT Nursery sources).
Stock type Cavity Vol.
(ml)
PCT

Initial Height
(SE) (cm)

2

5-12
PCT

8

4-10
PSB

9

4-15

Initial Diameter
(SE) (cm)

20.9

3.86

(0.35)

(0.07)

25.2

3.69

(0.32)

(0.05)

15.8

3.01

(0.35)

(0.05)

Tree Density
(#/m2)
280

Est. Cost
($)
0.400

527

0.225

527

0.22

3.4 Stock Sorting and Pruning
All seedlings were shipped to the Enhanced Forestry Lab at the University of
Northern BC (EFL-UNBC) in May 2005. The PCT 5-12 and PSB 4-15 were in
excellent condition, however, many PCT 4-10 showed signs of detritus fungi on their
lower foliage associated with the stress of thaw during shipment. Once received,
seedlings were kept at 4 °C in a walk-in cooler for sorting and seedling preparation.
Seedling sizes in various stocks varied extensively. Removing the outliers according
to height, diameter, and root density minimized variations in sizes among seedling
populations. For the PSB 4-15 and subsequent knife pruning treatments, stock was
first divided into five piles of 45 seedlings then bagged and randomly selected for
knife root pruning treatments. All seedlings were colour-coded using plastic strap to
identify the imposed treatment throughout the duration of the experiment.
Mechanical knife pruning was conducted only to the PSB 4-15 stock with the
use of a fillet knife and a plastic tube template with pre-established slits inserted for
each treatment type (Fig. 3.7).

Treatments were thus unbiased to specific root

32

location with each tree receiving similar severity and location of knife cuts. Fig. 3.8
demonstrated washed replicates for each of the root pruning treatments prior to
planting.

Figure 3.7. Mechanical root pruning to PSB 4-15 stock. Materials used: A) fillet knife,
B) plastic tube pruning template, and C) colour-coded identification straps.

Figure 3.8. Mechanical root-pruning treatments for PSB 4-15 stock. Arrows point to cut
locations. PSB 4-15 - control (uncut); RPB - bottom 2 cm cut; RPB+2 - bottom 2 cm
and two perpendicular cuts at 4 and 8 cm down the plug; RP3 - three tangential cuts, 1
cm deep and 2 cm long, at 3, 6 and 9 cm at 120 ° from each other; RP6 - six tangential
cuts, 1 cm deep and 2 cm long, at 2, 4, 6, 8, 10 and 12 cm at 90 ° from each other.
33

Table 3.3. Seedling stock types tested and root pruning treatments.
Stock

Treatment

Action

PCT5-12

Chemically Pruned

Container with copper based paint

PCT4-10

Chemically Pruned

Container with copper based paint

Control group

No action - control group

RPB

Knife Pruned: Bottom 2cm cut off (removes most root
tips).

RPB+2

PSB4-15
RP3

RP6

Knife Pruned: Bottom 2cm cut and two 2cm wide
perpendicular cuts through the entire plug, at 4 and 8 cm
down the plug (removes most root tips and cut some
structural roots and fine roots)

Knife Pruned: Three tangential cuts, 1 cm deep and 2 cm
long, at 3, 6 and 9cm down the long axis of the plug;
progressively 120 degrees from each other spiralling
down the plug (removes structural roots and fine roots
mostly to upper plug).
Knife Pruned: Six tangential cuts, 1 cm deep and 2 cm
long, at 2, 4, 6, 8, 10 and 12 cm down the long axis of
the plug, 90 degrees progressively from each other in a
spiral (removes many structural and fine roots).

3.5. Planting and Brushing
On May 11 and 12, 2005, seedling trials were established at the Red Rock and
Aleza Lake sites, respectively. A total of 25 replicates for each stock type and
treatment were planted at each site. Seedlings were planted by the author to minimize
any planting bias. The experimental design had treatment replicates planted in an
alternating series of blocks (rows) so that each treatment had equal representation
across a possible site change. At either site, seedlings were planted in blocks of 5-7
replicates per treatment with inter-tree spacing variable to select for best microsite (1
metre minimum spacing). Microsites selected at Aleza Lake consisted of raised
34

forest floor spots away from excessive decayed wood, brush, roots, and stumps.
Typical of duff planting technique, only coarse forest litter and harvesting debris were
removed at each planting spot.
Planting was done typical of industrial forest operations.

Seedlings were

inserted by the rooted plug into the ground buried 1-2 cm past the root collar. With
the hard soils at Aleza Lake, the planting shovel was used to chop the soil several
times in preparation of planting as well as when pressing the soil around the newly
planted seedling. This effort helped break up compacted soil associated with opening
the hole in the hard clay. Trees were given a light tug to ensure a snug fit. Both sites
were brushed on occasion to reduce but not remove the effect of vegetative
competition. This was done with hand pulling and hand pruning three times over the
growing season.

3.6. Initial Biomass Measurement - Shoot Mass, Root Mass, Shoot to Root Ratio
Ten seedlings for each treatment were selected. Each was hand washed with
water using a spray gun to remove the peat from the plug for the determination of
biomass. Samples were inspected to remove debris and cut roots. Seedlings were
severed at the root collar to separate root mass from shoot. Roots and shoots were
placed separately in paper bags and oven dried for three days at 70 °C. Biomass of
shoot and root was weighed using a digital scale with accuracy of 0.01 grams. Shoot
to root ratio was calculated from the results of biomass measurements according to
the following:
Shoot to Root mass fraction = shoot mass (g) / root mass (g)

35

(3)

3.7. Field Root Growth Capacity Test
After 21 growing days, 10 seedlings of each stock treatment, at the Red Rock
site were used for the Field - Root Growth Capacity test (Field-RGC). A Field-RGC
is similar to the industry practices where RGC is determined under controlled
conditions in a growth chamber. RGC test is used as an industry standard to provide
a comparative assessment of the vigour of the initial growth of a given stock (Ritchie
and Dunlap, 1980; Burdette et al., 1983).
The standard variable in RGC test is Total Root Count determined as number
of roots whose length > 1.0 cm. All roots counted were partitioned to plug location
as Side and Bottom growth development.

3.8 One-Year Pine Tree Measurements

3.8.1 Survival
In early September 2005, seedlings were assessed for tree vigour as Good, Poor
and Dead.

Parameters used to assess vigour were to account for: general stem

deformities such as a fork, frost or insect damage, excessive vegetative competition,
moose hoof compaction, and browse. Poor and Dead individuals were removed from the
measurement sample population. A Good tree had minimal degree of deformities, while
a Poor seedling had obvious growth impairments.

3.8.2 Relative Growth Height (RGH) and Diameter (RGD)
Initial Height (Hi) and Diameter (Di) were measured soon after planting on
May 11-12, 2005.

Height and Diameter were measured initially after planting.

36

Height was measured to the nearest 0.5 cm from the ground to the tip of the terminal
bud. A digital calliper was used to obtain an accuracy of 0.2 mm in measurements
taken for diameter just above the forest floor. In September 2005, after cessation of
leader growth and bud set, seedlings were re-measured for final Height (Hf) and
Diameter (Df). For growth calculations, relative growth was used to correct against
differences in Hi and Di across sites and treatments at the time of planting. The
relative growth was calculated as follows:
Relative Growth Height (RGH) = In (Hf) - In (Hi)

(4)

Relative Growth Diameter (RGD) = In (Df) - In (Di)

(5)

3.8.3 Mid-Leader Needle Length
Mid-leader needle length of the current year's growth was measured as an
indicator of tree vigour and site quality. Mid-leader needle length was used as an indirect
measure of growth associated with potential growth shock associated with root pruning
and poor root establishment (Burdette et al., 1984). Needle length was calculated from
the mean length of three pairs of needles from the mid leader of the current year's growth
to the nearest 0.1 cm.

3.8.4 Root System Excavation Method
Sixteen trees from each treatment were randomly selected for excavation to
investigate the growth of root systems from the entire sample population minus the trees
found to be poor conditions. At Red Rock site, seedlings were excavated to a depth of 50

37

cm, within a 40 cm radius around the tree, using spade shovels. Prying and agitating then
fractured the soil column and the tree root system was easily recovered.
At Aleza Lake site, the cohesive nature of clayey soils required the use of a
large steel core (10 cm radius, 25 cm long) to excavate the seedlings. The seedling
was cut at root collar and the steel core was fitted around tree and pounded into
ground using the 10-kg slide hammer. A shovel was used to excavate the soil core
with the root system intact. Samples were stored in bags and taken to laboratory for
assessment of soil structure and root development (Fig. 3.9).

Figure 3.9. Steel core apparatus (left) and a soil core with root system (red tag) (right) at
the Aleza Lake site.

38

3.8.5 Root Symmetry
Each excavated seedling was washed with water to remove soil and peat materials
prior to assessment of planting deformities in the root system.

Symmetry was

assessed from the radial development of the root system in each quadrant around the
root collar. A discrete interval scale from 1 - 4 as shown in Fig. 3.10 was used in the
assessment.

Unidirectional - 1

Bilateral symmetry - 2

Three quadrants of growth -3

Figure 3.10. Root symmetry classes used in the assessment of root growth. 1 - one
direction usually straight down; 2- bilateral growth usually in opposite direction; 3lacks growth in one direction; 4- balanced growth in all direction (picture not shown).

3.8.6 Total and Large Root Counts
Root abundance was divided into Total Root Count (TRC) and Large Root
Count (LRC). For each category, counts were partitioned according to location of
egress from the plug as follows (Fig. 3.11): Top (upper 3 cm), Middle (rooting area
between Top and Bottom), and Bottom (bottom 2cm). Total root count included all
but the following: senesced roots and roots < 5 cm. Large roots were characterized as

39

those that have secondary growth characteristics: yellowish in colour with sloughing
of the brownish outer cortex and thicker diameter. Only top ten largest roots were
counted although some replicates had < 10 large roots and others >10.

Figure 3.11. Tree root system showing Top, Middle and Bottom plug locations.

3.8.7 Large Root Deformity
Large root deformity was assessed from the ten largest roots selected. The
degree of root deformity was grouped as Braided, Kinked or Direct (Fig. 3.12).
Braided roots have twisted primary roots prior to growth trajectory while Kinked

40

roots exhibit kinks or points of obvious weakness.

Direct roots showed no

recognizable deformities or intertwining and are considered free to establish as
structural primary roots without the likelihood of deformity. Direct roots included
those that have deflected downward along the wall of the plug and may include some
degree of lateral deflection such as a bend (a sharp bend however, would be
considered a kink).

Direct Root

Kinked Root

Braided Roots

Figure 3.12. Pictorial examples of root deformity classes.

3.8.8 Taproot Development
Taproot development was evaluated as binary nominal classes of Yes or No.
In the Yes category, taproot displayed a large primary root with characteristic
secondary growth similar to criteria for large root count (Section 3.8.6). The No
category had taproot without differentiated secondary growth.

41

3.9 Statistical Analysis
A 2-way ANOVA (analysis of variance) using SYSTAT (version 11, 2004)
was used to compare means between site and treatment for root counts and tree
measurements at P-value < 0.05. Tests for normal distribution and similarity of
variance were conducted prior to ANOVA with Box Cox transformations used on
variables where distribution was not normal and/or variances not equal (Box and Cox,
1964). Post hoc Bonferroni pair wise comparisons were used to compare treatments.
A Logistic Regression Model was used for the discrete variable of taproot
development (yes, no) and an Extended Logistic Model was used for the 4-class scale
of symmetry.

Logistic Models were conducted using SAS version 9.1.3 (SAS

Institute).

42

4. Results
ANOVA and logistic regression tables are presented in Appendix E.
4.1 Site Volumetric Moisture Content
Average monthly precipitation normals (1975-2000) for Prince George weather
station (Airport) indicated that the 2005 growing season started with the month of April
being 64% drier than normal, but by mid summer, July was 145% wetter than average.
Over the growing season, volumetric moisture content (VMC) of the Lower stratum (2030cm) at Aleza Lake demonstrated a 9% variation between 39% VMC (mid-summer) and
48% VMC (mid-fall). A 13% seasonal variation was observed at Red Rock varying from
14%-27% VMC (Figs. 4.1 and 4.2) during the same period. At Aleza Lake, VMC of the
Upper and Lower strata differed only slightly (Fig. 4.1). At Red Rock, however, Upper
soil stratum typically retained less moisture than Lower stratum (Fig. 4.2).

• Upper 0-10cm
• Lower 20-30cm

°/<VMC

May13

Jul-26

Oct-24

Figure 4.1. Site Volumetric Moisture Content from a composite of 16 cores at fixed
locations for Upper and Lower strata at Aleza Lake site during the 2005-growing season.

43

50
45
40

• Upper 0-10cm
D Lower 20-30cm

35
30
%VMC

25
20
15
10

tm HH
>

^**

3 *f

NN

.<*

N^

^

^v N
.e.-<

„,*>

rV

$>

&

rKV

Figure 4.2. Site Volumetric Moisture Content from a composite of 16 cores at fixed
spots for Upper and Lower strata at Red Rock site during the 2005-growing season.

A one-time fall volumetric soil moisture was measured as a baseline of inherent
site variation (Figs. 4.3 and 4.4). Aleza Lake's wetter clayey forest soil showed random
site variation with a mean volumetric moisture content and standard error of 47 % ± 0.80
(Fig 4.4), while Red Rock's ploughed sandy field had a more uniform variation and lower
mean moisture content of 21 % ± 0.39 (Fig. 4.3).

44

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4.2 Seedling Initial Biomass
A large range in initial root and shoot mass was tested owing to large variation
within and among the different stock sizes and knife prune treatments. Ten replicates
were tested for each of the 7 treatments. Mean initial root mass (± SE) ranged from
0.52g ± 0.037/seedling for the RP6 treatment to 1.60g ± 0.103/seedling for the PCT 5-12
treatment. Initial shoot mass ranged from 1.40g ± 0.10/seedling for PSB 4-15 and all
subsequent knife pruned RP treatments to 4.10g ± 0.285/seedling for the PCT 5-12
treatment.
As compared with the PSB 4-15 control group, knife-pruning treatments (RPB RP6) demonstrated a negative mean root mass trend as a consequence of the increasing
severity and frequency of cuts (Appendix C). With the PCT and PSB seedlings, there
showed distinct mean initial root mass differences reflecting the different container sizes
with PCT 5-12 > PSB 4-15 > PCT 4-10. Initial shoot mass differences were established
as PCT 5-12 > PCT 4-10 > PSB 4-15 (Appendix C).
Shoot to root ratios showed that the PCT 4-10 treatment had the greatest amount
of shoot compared to its small root while the PSB 4-15 had the greatest amount of root
relative to a smaller shoot. The larger PCT 5-12 stock had shoot to root ratios in the
middle of this range (Fig. 4.5). Among knife pruning treatments all but the RPB pruning
treatment (RPB+2, RP3, RP6) were associated with higher shoot to root ratios compared
to the uncut PSB 4-15 control matching the shoot to root ratio of the PCT 512 treatment.

46

\<bx

/vV

,.«£

Treatment

Figure 4.5. Mean and standard error for initial shoot to root ratios for stock type and post
knife-pruning treatments, (n = 10). Treatment means with same letter are not
significantly different (P>0.05).

4.3 Roots Cut in Plug as a Consequence of Knife Pruning
Observed in RPB+2, RP3 and RP6 treatments was increasing numbers of large
roots cut in the upper and mid plug with an increasing frequency and severity of lateral
cutting (Fig. 4.6). While the RPB, bottom cut treatment, had large roots pruned, these
only occurred at the bottom of the plug.

47

,

T

-

o

i

T

T
0)
m

^

-

1

-

a

b

b

RPB + 2

RP3
Treatm ents

Figure 4.6. Mean and standard error estimate of large roots cut within upper plug
as a result of each knife-prune treatment. Treatment means with same letter are
not significantly different (P>0.05).

Also the frequency of tap-roots cut in the upper plug varied depending upon the
method and severity of lateral cuts in knife-pruning treatments (Fig. 4.7). The RPB+2
treatment with two deep cuts showed a similar effect as 6 more shallow tangential cuts.

RP3

RP6

Treatments

Figure 4.7. Incidence of tap-root cutting in the upper plug region in knifepruning treatment (both site combined).

48

4.4 Seedling Performance After One Growing Season: Aleza Lake and Red Rock
4.4.1 Survival and Sample Size
Prior to root excavations in September 2005, all seedlings in treatment
populations (N) at each site were surveyed for vigour and survival (Table 4.2). After one
growing season, survival was 100% except for the PCT 4-10 stock. This stock also had
shown pre-treatment signs of stress evident as detritus needle fungi from extended thaw
period as a result of shipping. Seedlings with damage or growth impediments were
classed as poor vigour. These were a consequence of excessive vegetative competition,
brushing injury, hoof press and rabbit browse.
From the initial sample populations of 25 replicates per stock and treatment, only
trees with good vigour were selected for stem measurements (Table 4.2). From these, 16
trees were randomly selected for root measurements. Unfortunately occasional damage
occurred to Aleza Lake samples reducing some of root sample sizes (n) producing an
unbalanced design.

Table 4.2 Initial numbers of seedlings (N) showing degree of vigour, survival and
randomly chosen root sample size (n) at study both sites after one growing season.
AL=Aleza Lake, RR=Red Rock.
n

Site

N

Dead Poor Good

n

24

14

RR

25

0

0

25

16

2

22

16

RR

25

4

4

17

16

0

0

23

16

RR

25

0

0

25

16

0

0

1

24

15

RR

25

0

1

24

16

25

0

0

7

18

15

RR

25

0

1

24

16

AL

25

0

0

5

20

16

RR

25

0

2

23

16

AL

25

0

0

7

18

14

RR

25

0

2

23

16

Treatment

Site

N

Lost

Dead Poor Good

PCT 5-12

AL

25

1

0

0

PCT 4-10

AL

25

0

1

PSB4-15

AL

25

2

RP1 4-15

AL

25

RP2 4-15

AL

RP3 4-15
Rp6 4-15

49

4.4.2 Relative Growth - Height, and Diameter
Relative Growth Height (RGH) (Fig. 4.8) and diameter (not shown) were
significantly different for site (P<0.01) and treatment (P<0.01). Seedlings at the Aleza
Lake site had greater relative growth in height and diameter than seedlings at Red Rock.
Among the treatments, the initial tallest of tested stock, the PCT 4-10, were the only
treatment to show significantly lower relative growth (Fig 4.8.A). This occurred against
only the PCT 5-12 and PSB 4-15 (PO.01), at both sites. After the first year's growth,
RGH values among knife-pruning treatments (RP) were not significantly different
(P>0.05) than the non-pruned PSB 4-15 control.
Height
50

Relative Height Growth
1.0

• • Red Rock after one growing season
I
I Aleza Lake after one growing season
• m i Initial height (both sites averaged)

0.9
0.8

Red Rock*
Aleza Lake

I
X
I

0.1 H

.^Vt^!V*> ? > ? 6
V " v\^>^"

k-x"

^*<Z*<***Z<*i**l++'
^"t/f>
*•'

*-'

Treatment
Treatment
(A)
(B)
Figure 4.8. (A) Comparison of mean and standard error between initial height (cm) (both
sites averaged with no significant differences) and final height after one field-growing
season; and (B) mean and standard error for Relative Growth Height after one-growing
season at Aleza Lake and Red Rock sites (* indicates significant site differences P<0.05).

50

4.4.3 Mid-Leader Needle Length
A 2-way ANOVA of needle length detected significant differences for site
(P<0.01) and treatment (P<0.01) (results not shown). Seedlings at Aleza Lake had longer
(9.5cm) mid-leader needles than Red Rock (7.7cm). Among treatments the PCT 4-10
seedlings produced shorter needles than all other treatments consistently at both AL and
RR sites. No interaction effects between site and treatments were observed.

4.4.4 Root Symmetry
No site differences and strong treatment differences were observed in a 2-factor
extended logistic regression for seedlings response in root growth symmetry.

Three

benchmark treatments: PCT 4-10, PSB 4-15 and RP6 4-15 were use to compare the odds
ratio estimates against all the other treatments with 95% confidence.

Frequency

distribution of Root Symmetry classes shows how root-pruning treatments, both chemical
and mechanical significantly improved root symmetry over the un-pruned control PSB 415 (Fig. 4.9). Comparing root symmetry classes against base-line treatments, the PSB 415 and RPB treatment were least symmetric, while the rest of the pruned treatments
(RPB+2, RP3, PCT 4-10, PCT 5-15) proved not different. Odds ratio comparisons
showed:
PCT 4-10, PCT 5-12, RPB, RPB+2, RP3, RP6 > PSB 4-15
PCT 5-12, RPB+2, RP3, RP6 = PCT 4-10 > PSB 4-15, RPB
PCT 4-10, PCT 5-12, RPB+2, RP3 = RP6 > PSB 4-15, RPB

51

Treatment

Figure 4.9. Percent frequency distribution of root symmetry classes among treatments
after one- growth year (data pooled among non-statistically different sites).

4.4.5 Root counts after 21 days: Red Rock Field Root Growth Capacity Test
A one-way analysis of variance (ANOVA) showed significant treatment
differences in root counts after 21 days. The largest stock type (PCT 5-12) produced the
greatest root numbers over any other treatments tested (Fig. 4.10). While the PCT 4-10
and PSB 4-15 had similar Total Root Counts, the PSB 4-15 control demonstrated the
lowest average proportion of side root development. Plugs whose bottoms were severed
in knife pruning treatments (RPB and RPB+2) had significantly lower proportions of
bottom roots developing after 21 days (P<0.05). RP3 and RP6 knife pruning treatments

52

also demonstrated reduced mean total root counts but transformed means were not
statistically different to the uncut PSB 4-15 control.

Treatm ent

Figure 4.10. Mean and standard error for total, side and bottom root counts > 1 cm at
Red Rock site (n = 10) for the 21 day test.

4.4.6 Root Counts After One-Field Growing Season: Aleza Lake and Red Rock
Significant site (P<0.01) and treatment (PO.01) differences in root counts were
observed after one growing season. Aleza Lake site produced significant albeit minor
increased counts compared to Red Rock (Fig. 4.11). Similar to the Total Root Count
(TRC) treatment trend after a 21-day growth period, the larger sized PCT 5-12 plugs
produced significantly more roots than any other treatment. Both bottom plug removal
treatments, RPB and RPB+2, showed reduced counts for both sites as compared to the
uncut control (P<0.01).

53

120

I

100

I
•£

80

o
O
o
o

60

on
"5
**
o

^ H Red Rock*
i
i Aleza Lake

I
•£

40 H

20

G^

,S«
vA*

.\*

^
A*

^

^
^

<,*-??
^

Treatment

Figure 4.11. Mean and standard error for total roots counted after one growing season at
Aleza Lake and Red Rock sites. (* indicates significant site differences).

Since stock size showed a positive influence on total root numbers, root counts
were partitioned according to relative contribution to plug location: top, middle and
bottom (Fig 4.12). Top root growth was proportionately greater at Aleza Lake relative to
Red Rock (P<0.01), while bottom root growth was proportionately greater at Red Rock
relative to Aleza Lake (P<0.01). The proportional contribution of mid plug roots showed
no site differences.
Among treatments, the PSB 4-15 was the most restricted to bottom root growth
regardless of site. As compared to the non-pruned PSB 4-15, knife pruning significantly
increased the proportion of middle roots and reduced the proportions of bottom roots,
while top root showed mean differences consistent with both sites but these were not
significant.

54

^G>C>#v^^V^^

r^<^<^'>K^

Treatment

Treatment

(A)
(B)
Figure 4.12. Mean proportion of total roots counted partitioned to top middle and bottom
plug location at sites:(A) Red Rock and (B) Aleza Lake.

4.4.7

Large Root Counts
Large root counts (LRC) showed site and treatment differences (P<0.01) (Fig

4.13). At Red Rock, typically seedling root systems had more than 10 LRC, while at
Aleza Lake most root systems had less than 10 LRC. Site x Treatment interaction was
also significant (P<0.05). Reduced large root counts were observed in the control PSB 415, particularly at the Aleza Lake site. Relative to the uncut PSB 4-15, lateral-cutting
methods in the knife prune treatments, RPB+2, RP3 and RP6, showed increases in LRC.

55

Red Rock*
Aleza Lake

I—I
10

I

Li«j

I

c
o
O
o
o
CH
<D

P>

3
o

4

H

c

03
CD

2 H

^
^

A©

^

-

.

A*

,

*

*

.

«

•

•

vA*

^

^

^

*tf°

A*

Treatment
Figure 4.13. Mean total large roots counted and standard error (up to a cut off of 10)
after one growing season at Aleza Lake and Red Rock sites. (* indicates significant site
differences).
When large root counts were partitioned to relative contribution, according to
plug location, sites influenced root location preferences as: middle > bottom > top for
Red Rock and top = middle > bottom at Aleza Lake (Fig 4.14). Compared to total roots,
large roots were more frequently developed in the top and middle plug locations, rather
than from the bottom. Among treatments, the chemically pruned stock showed relatively
low variation in root partitioning between sites, where as the PSB 4-15 and knife pruning
treatments demonstrated site adaptation.

56

Aleza Lake

Red Rock

.«^<*K*f^l*K***

^<^<^t^<^K^l^
Treatment

Treatment

(A)
(B)
Figure 4.14. Mean proportion of large roots partitioned to top, middle and bottom plug
location after the first growing season at sites: (A) Red Rock (n=15) and (B) Aleza Lake.

4.4.8

Root Deformity Among Large Roots Counted
The mean percentage (and standard error) of non-deformed Direct Large Roots

(DLR) at Aleza Lake was 48 % ± 2.7, significantly higher than the DLR at Red Rock at
37 % ± 2.6. The effect of treatment was also detected in DLR. The PSB 4-15 control
and RPB treatment had the lowest DLR values tested while the PCT group had the
highest mean proportions of DLR (Fig. 4.15). As compared with the control PSB 4-15,
knife pruning with lateral pruning treatments increased mean DLR approaching values
comparable to the chemically pruned PCT 4-10.

57

100

"o
o
OH

90

ab

80 -

d

dc

b

be

be

CD
CO

o
CD

70 -

m

60 -

L—

Q
o
•4—

o
c
(u
o
I—

50
40
30

i

CD

D_
c
CO
CD

20
10

»***

«***

* * * * * . < > * *

^

»**

Treatment

Figure 4.15. Treatment mean and standard error for the proportion of direct large roots
after one-year for both sites combined. Means with same letter are not significantly
different (P >0.05). Sites were significantly different (P<0.05).

4.4.9 Tap-Root Development
Tap-root development showed a poor trend as compared to the rest of the
measured variables. Among sites and treatments, the population with secondary tap-root
growth occurred 55% of the time. Analysis using logistic regression of tap-root
development after one growing season was analysed for two factors: site and treatment.
No site difference was observed (Fig. 4.16). Occasional treatment differences were
detected when three bench-mark treatments: PCT 4-10, the PSB 4-15 and the RP6 4-15

58

were used to compare against all the other treatments with 95% confidence. In all cases
when comparisons were analysed, the RP6 and RPB+2 showed significant increases in
tap-rooting; all other treatments showed no difference.
RP6, RPB+2 > PSB 4-15 = PCT 4-10, PCT5-15, RPB, RP3
RP6, RPB+2 > PCT 4-10 = PSB 4-15, PCT5-12, RPB, RP3
RPB, RPB+2, RP3, PCT 5-12 = RP6 > PCT 4-10, PSB 4-15

100
90

^ M Red Rock
re-sw i Aleza Lake

80
c
a>
E
a.
.o
©
>
CD

T3

70
60
50

"S
O
i_

40

a.
30 20 10 0

• .\v

A*

A^

^
W&

OK'

Treatment

Figure 4.16. Percentage of treatment population with detected secondary growth in taproot after one-year growth for Red Rock and Aleza lake sites.

59

5. Discussion
5.1 Site Differences and its influence on Seedling Growth and Development
Many of the measured growth variables demonstrated significant site differences,
an indication of contrasting productivity in the two sites studied (Narukawa and
Yamamoto, 2003; Jones et al., 2002; Balisky and Burton, 1997; Heinemann, 1991;
Becker et al., 1987). Improved seedling height and diameter growth at Aleza Lake is
likely the result of higher moisture and nutrient availability.

Also root growth

parameters, including the extent and location of root egress, were strongly dependent on
soil type give rise to characteristic rooting patterns (Narukawa and Yamamoto, 2003; Eis,
1970).
For example, in dry soils, seedlings need to establish their root systems rapidly at
the cost of height growth developing high root to shoot ratios (Preston, 1942). Enhanced
root differentiation in dry soils explains why Red Rock seedlings had greater large root
counts over total roots counted. Low water availability in Red Rocks upper 10 cm
explains why roots were restricted in development in the uppermost plug (Fig. 4.14).
Seedling root trajectories were oblique to steeply descending. Limited water retention
capacity in the upper soil strata can be explained by the absence of a forest floor in
addition to sites dominated by sandy texture (Fig. 4.1). Forest floors also buffer the
evaporative demand, reflecting and insulating mineral soil from solar radiation
(Heineman, 1998). Finally, observations made during seedling excavation, the extent of
roots of some individuals exceeded 100 cm in lateral and 50 cm in vertical direction.
In contrast to Red Rock, the dominant root growth at Aleza Lake was in the upper
and middle sections of the plugs where rooting trajectories were observed to be

60

horizontal to oblique. Enhanced rooting at the soil surface is, in part, the result of poor
soil drainage causing water saturation and anaerobic soil conditions. This restricts the
development of roots with closer to the soil surface (Xu et al., 1997). Also, surface soils
have higher nutrient availability because of the humus-rich forest floor (Brady and Weil,
1996).
Red Rock showed increased proportion of deformed large roots because there
were a greater proportion of these to emerge out of the bottom of the plug. Increased
deformity in the bottom of the plug is likely the effect of the container. As roots are
deflected from their outward trajectory down the long axis of the container wall, they are
more likely to interact with each other and braid (Balisky et al., 1995). Braided roots are
prone to root balling, the subsequent disproportionate swelling of the plug (Winter and
Low, 1990). Root balling occurs when root deformities are severe enough to impede the
translocation of sugars within the phloem and concentrate an exaggeration of growth
above root constrictions (Hay and Woods, 1978).

5.2 Field Root Growth Capacity at the Red Rock site
Root growth capacity (RGC) after 21-days was shown to be a useful tool for a
rapid assessment of stock vigour and the potential rooting locations for PSB and PCT
seedlings. Low total root counts in the bottom cut knife pruning treatments: RPB and
RPB+2 might indicate poor stock performance (B.C. MOF, 1998), this claim however,
was not reflected in decreased height growth needle length after one growing season
under the tested site moisture regimes. A longer time frame is required in interpreting the
results if height is impeded by pruning method or extent.

61

Reduced initial root counts may not be as important to seedling survival or growth
as is the ability to develop non-deformed primary roots in the optimum soil conditions.
For example, naturally germinated seedlings have far fewer roots than planted stock,
however, these are of primary root types situated typically near the surface soil, well
developed, expanding and branching extensively into the soil environment (Eis 1978,
Horton 1958).

Also, rooting development may not establish exclusively from pre-

existing root tips within the plug. Adventitious roots emerge gradually and can be
responsible for much of the structural roots as found in planted spruce seedlings
(Heineman et al., 1999; Coutts et al., 1990). In the knife-pruned treatments, many
adventitious roots emerged from the "wounds" resulting from knife pruning cuts. These
roots likely developed after a lag time required for the "wounds" to heal. Considering the
rooting delay, knife-pruning may compromise planted trees only in the driest of sites or
seasons found in the BC interior.
Finally, the RGC test is limited in its application to assess the performance of outplanted stock considering the characteristic rooting patterns of seedlings planted under
contrasting soils. For example, in very wet or cold soils, where rooting is limited with
soil depth, stock types, like the PSB with its aggressive bottom plug growth, may perform
sub-optimally with fewer root counts closer to the soil surface.

5.3 Comparison of Root Growth and Development Between Stock Types
The initial biomass ratio of the non-pruned PSB 4-15, with the lowest initial shoot
to root ratio, proved to be a poor predictor of seedling performance with no differences in
height growth detected after one year.

In terms of root growth morphology, more

62

important than initial root biomass is the initial root arrangement, which, in the case of
the PSB 4-15 stock was mostly limited to bottom of the plug development. This style of
growth, similar to a showerhead, showed the poorest development in root symmetry and
greatest incidence of large root deformity. Dominant bottom root development, found in
PSB 4-15 stock, agrees with the results of Heineman (1991), and Balisky and Burton
(1997). PSB stock are, therefore, less likely to adapt to sites where rooting is best
developed in surface soils. Examples of sites unfavorable to root development in surface
soils include cut-blocks in central interior of BC where sites have cool soil temperatures
(Balisky and Burton, 1997), reduced aeration, poor drainage (Heineman, 1991), scalped
soils and increased soil density (Wass and Smith, 1994). Speculation exists whether root
development where restricted to the bottom of the plug and deeper in the soil, as observed
in the PSB 4-15 stock, particularly in the longer stock sizes, are more likely to be
susceptible to stressful environmental episodes. PSB stock with greater bottom root
development may be more responsive to site preparation designed to ameliorate soil
conditions to achieving more vigorous establishment growth (Bedford and Sutton, 2000).
The PSB 4-15 stock scored lowest in large root tallies and showed the highest
incidence of deformed large roots at both sites. Reduced number of large root counts in
the PSB 4-15 stock could be due to their excessive root deformation leading to root
balling and reduced distal growth. Reduced root symmetry in the PSB 4-15 stock is
similar to the findings from a 5-year lodgepole pine trial by Winter and Low (1990). This
suggests that developmental symmetry is a phenomenon that may have longer-term
implications to tree growth.

Since root tips grow in the direction of their initial

orientation (Puhe, 2003), reduced root symmetry occurs because most of the root tips are

63

typically pointed downward at the bottom of the plug. Greater root symmetry of large
roots may show for greater resilience from mechanical forces that act on a stem as from
wind, competing vegetation, snow press and from frost wedging during soil freeze-thaw
events.

Forces acting on the stem lead to curvature (Courts et al., 1999).

Higher

incidences in stem curvature in PSB stock of lodgepole pine has been reported by
Krasowski (2003). Stem curvature can lead to the development of compression wood
detrimental to wood structural properties (Rune and Warensjo, 2002).
Compromised root growth demonstrated as reduced root symmetry, reduced large
root counts and high incidence of large root deformity suggests that PSB seedlings has
difficulty recovering from their containerized 'root-bound' conditions. Salonius et al.
(2000) demonstrated in black spruce PSB seedlings that increased growing space led to
higher photosynthate allocation to root over shoot and resulted in increased root density
due to continuous root branching within the plug and the development of mature
suberized root systems. However, Salonius et al. (2000) found that these over-developed
plugs had poorer field growth performance as compared with seedlings grown at limited
spacing with low root densities and more juvenile root systems.

Norgren (1996)

explained that as a colonizer species of disturbed soils, lodgepole pine have fast rates of
root growth, particularly in fine root production, suggesting shorter cultivation times for
container stock to avoid subsequent root deformation and root instability.

5.4. Root Growth and Development Among Root Pruning Treatments
Root pruned seedlings consistently produced superior root growth (e.g., balanced
symmetry, low large root deformity, higher development of large root) relative to the

64

non-pruned control seedlings. In addition, chemically pruned PCT (5-12 and 4-10) stock
had greater incidence of top and mid plug development similar to the findings of Jones et
al. (2002).

When out-planted, the initiation of the dormant primary roots is again

favoured as is demonstrated by increased incidence of large root counts (Fig. 4.13) and
with more even root distribution throughout the plug (Fig. 4.14).
Cases of seedling mortality, reduced relative height growth, and shorter needle
length, were observed only in the PCT 4-10 stock at both sites. This was likely caused by
the stock's poor condition as a result of shipping stress. Mortality was greater at the Red
Rock site suggesting it was exacerbated by low available moisture.

However it is

unlikely that the rooting pattern of this PCT 4-10 stock would change too drastically in
response to the different soil types. Thus the relative growth if not the absolute in
measured root parameters for this stock is still likely to be valid.
Growth results among the knife pruned treatments showed resilience to losses in
initial root biomass with no reductions to stem growth after the first field-growing season.
Based on the observed roots counts after 21 days, knife pruning treatments with lateral
cuts showed better results than bottom plug removal cuts because the former did not
significantly depress total roots counts in their early establishment.

In addition to

retaining a greater numbers of initial root tips, lateral pruning methods dispersed roots to
a greater distribution throughout the plug. New adventitious roots grew in more outward
directions created from the "wounds" left behind by cuts of the knife. Knife cuts to the
mid-plug reduced the propensity of root braids reducing root deformity. While knifepruning methods, RPB+2, RP3 and RP6, were statistically equivalent (Symmetry, Large
Root Count, and Direct Large Roots) to chemical root pruning, the latter had root systems

65

that still appeared more natural with a more consistent rooting pattern, reduced large root
bending and inter-root constrictions within the plug.
It remains unclear if knife pruning stimulates tap-root development in early
seedling development. Only two of three lateral cutting treatments showed statistically
significant increases in tap-root development. When the replicates base from both sites
were pooled and tap rooting was compared by seedlings that did not have their tap-roots
cut (94 cases from PSB 4-15, PCT 4-10 and PCT 5-12), only 49% showed tap-rooting
with secondary growth; this compared to 63% with tap-roots showing secondary
development in those replicates that had their tap-root knife pruned in the lower plug (47
cases of knife prune bottom cut treatments: RPB and RPB+2); and 71% showing tap-root
development from the 35 cases when lateral pruning severed the tap-root in the upper
plug (RPB+2, RP3 and RP6). Since development for lodgepole pine is considered a taproot dominant species particularly in well draining conditions (Eis, 1970), a study design
that properly examines tap-root development with root pruning is warranted considering
the beneficial attributes of tap roots dominance to tree rigidity and anchorage (Coutts et
al., 1999).
In this study, knife-pruning methods tested fell below the critical maximum when
growth and survival was compromised. It suggests that the PSB containerized seedling
has considerable resilience to root system manipulation. Since knife pruning reduced the
incidence of root deformities in the PSB 4-15 plug, in theory, continued knife pruning
should improve root growth parameters further. A critical maximum point should exist
however, where continued pruning would begin to show declines in stem growth (height,
diameter, and needle) and survival. Indeed detection of growth loss will be more clearly

66

evident by the second growing season. For example Bigras (1998) began to observe
declines in growth performance of containerized black spruce at 40% biomass removal in
her bottom plug removal technique. She also observed greater growth losses to diameter
than height with 19% and 13% growth loss respectively in her maximum 80% biomass
removal treatment. In another experiment, 50% destruction of the root system by root
freezing Jack pine seedlings showed losses to height growth (Bigras and Margolis, 1997).
A root-pruning maximum should also exist as treatments interact with the effect
of soil condition. For example, the harsher Red Rock site would likely tolerate less
pruning than Aleza Lake before growth losses and mortality is realized.

In this

experiment, the most severe knife pruning treatment, RP6, removed on average 60% of
the original root biomass, increasing the average shoot/root biomass fraction from 1.21 in
the control PSB 4-15 to 2.88. In future, pruning treatments should encompass a shoot
mass/root mass of up to 5 for sites in the BC interior. This will cover a greater pruning
range and provided better understanding of the consequences of the higher levels of
pruning treatments.
Significant height growth differences between sites but not among pruning
treatments agrees with the findings of Winter and Low (1990) and Jones et al. (2002)
supporting the theory that site has a greater effect on seedling growth than stock types or
pruning treatments. Certainly, a longer study period of study, say four years, would
provide better information on seedling growth differences among treatments because
growth differences can manifest over a longer period of time as was observed by Burdette
etal. (1983).

67

6. Conclusions and Management Implications

•

Root pruning treatments improved root growth
Chemical and knife pruning treatments produced superior root growth (e.g., balanced

symmetry, low large root deformity, higher development of large root) relative to the
non-pruned PSB 4-15 lodgepole pine seedlings, grown on two contrasting sites in the
interior of British Columbia. After one growing season, PCT and knife pruned seedlings
had at least 90% of their roots develop in at least three directions compared to <30 % in
uncut control (PSB). Root pruning increased the distribution of total roots throughout the
plug, increased the proportion of large roots, as well as reduced the incidence of large
root deformities. Among these aforementioned variables, chemical pruning treatments
consistently exhibited better results than the knife pruning methods. The incidence of
increased tap root development, however, may have increased with lateral cutting
methods with knife pruning. Indeed more research is required to properly determine the
long-term implications of root pruning on rooting development. The evidence presented
here, however, suggests that benefits of root pruning showed consistency across the
contrasting site conditions supporting its operational feasibility.

•

PCT stock offers improved rooting development
Improved root development and the readily available PCT treated seedlings in

commercial quantities makes PCT the preferred stock type over the PSB for reforestation
in northern British Columbia. The effectiveness of PCT, however, has shown to be
species limited but pine species such as lodgepole, white, and ponderosa as well as the

68

Douglas fir species have shown positive benefits (Krasowski, 2003; Wenny et al., 1988;
Burdette et al., 1983). Interior spruce species has shown little effect (Krasowski and
Owens, 2000). Due to species limitations and some environmental issues with the use of
heavy metal paint, alternatives in methods of root pruning should still be encouraged.

• Lateral rather than bottom cutting methods were favoured in knife pruned
seedlings
Lateral cutting was seen as more favourable than bottom cutting in terms of
stimulating root growth because it retains some of the active root tips at the bottom of the
plug and lead to higher initial root counts. Lateral cutting methods also improves the
total root distribution, produces more balanced root symmetry, has higher large root
counts and possibly increases tap root development. The intention for lateral pruning
should be to cut progressively down the plug to untangle and redistribute large roots.
Sufficient fine feeding roots should be retained for effective acquisition of immediate
moisture and nutrition. Operationally, knife pruning could be performed with a tool
attached to the bags of a tree planter where seedlings are pruned just prior to planting.
Alternatively, knife pruning could be mechanically done at the nursery before packaging
and cold storage.

•

Knife pruned stock must be handled with care
Knife pruned seedlings should be handled with extra care because pruning

treatments effectively reduce root density.

Reduced root density renders seedlings

susceptible to plug disintegrations with excessive handling.

69

Operationally this may

require innovations such as maintaining trees in a frozen state during planting as
suggested by Kooistra and Bakker (2005).

•

Seedling size and chemical pruning method
Growth parameters (e.g., height) of PCT 4-10 seedlings were better than other

stock sizes used in the thesis. After four months growth the PCT 4-10 were comparable
in root growth and height but not diameter when compared with the PCT 5-12. In
comparison to the PSB 4-15, the PCT 4-10 seedlings were taller and larger in diameter
with improved root development and root development than PSB 4-15 seedlings.
Presently, reforestation at the Aleza Lake Research Forest uses the PSB 4-15B
seedling. A stock type change to PCT 4-10 is warranted to improve root development at
a marginal additional cost. Also worth noting, the PCT 4-10 seedling was found to be
much more efficient to plant than the 5-12 or the 4-15 stock size due to their smaller plug
size. The 5-12 trees are awkward, requiring a big hole to accomodate the large plug
while the 4-15 seedlings are very long, making them more difficult to plant without
vertically compressing the plug or shutting the hole sufficiently without producing air
pockets in heavy Aleza lake clay.

•

Soil conditions influenced root growth
Site conditions such as soil properties significantly altered root size, abundance,

distribution, trajectory and percentage of rooting deformities of lodgepole pine seedlings
after the one growing season. The low volumetric water retention capacity in Red Rock
site restricted root development in the uppermost 10-cm of the plug. In contrast, the

70

dominant root growth at Aleza Lake was in the upper as well as in the middle sections of
the plug where water is still available.

The differential root development in two

contrasting sites highlights the importance of soil properties to root growth. Other results
imply the influence of soils on seedling performance and on management decisions such
as harvesting method, site preparation, stock size selection and planting method, species
and microsite selection.

•

Suggestions for future study
The results of one-year experiment provided a short-term benefits of root pruning

and identified areas that need to be addressed to understand the implications of pruning
treatments, soil conditions and stock types to the long-term seedling growth and
development. For example does root bind in PSB stocks have long-term implications to
seedling growth? Are the beneficial effects of root pruning species dependent? Will root
pruning improve seedling resilience to episodes of stress like climate, vegetation or
snow? There is a need for long-term experiments addressing root development in various
altitude-related seasonal temperature changes, growing substrates (mineral or organic),
vegetative competition, species, microsite, stock type, and planting techniques.

•

Possible changes in the legislation
The results from this thesis have shown that pruning improved the rooting

development of chemical and knife pruned seedlings of lodgepole pine. Although the
results in this thesis are short-term, if longer-term benefits of root pruning can be shown
to improve rooting development against a PSB stock, across species, stock sizes, and soil

71

conditions in a predictable and consistent outcome, it should be required by legislation.
With the principal reforestation objective of industrial forestry is to achieve free-growing
stocking standards, there exists no incentives to root prune since there is no confirmed
height growth or survival advantage. Should legislation be put in place that makes this
treatment mandatory, such a rule would be similar to the regulation that requires that
foresters to use due diligence to obtain the best possible seed (class 'A' seed is preferred)
available to a prescribed cut block.

72

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78

Appendix A. Mean and (standard deviation) of soil bulk density (g cm"3) at
various strata in Aleza Lake (n = 15) and Red Rock sites (n = 6).

Strata

Aleza Lake

Red Rock

Upper (0-1 Ocm)

0.70(0.130)

1.58 (0.042)

Middle (10-20cm)

1.08(0.095)

1.41 (0.050)

Lower (20-30cm)

1.24(0.163)

1.60(0.038)

79

Appendix B. Aleza Lake Summer Aeration (Aug.5- Sept 5, 2005) for 12 observations
across 60 m site (West -East) and the corresponding volumetric moisture contents on
Sept 5, 2005

Site Location West to East (m)

80

oo

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oo

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o

co

13
o
CO

n

+

co
co

i/i

co
co

o

o
1-1

P

P
S3
O

fro

Aeration Depth (cm)

% Vol. Moisture
Tilth Class

q

, ,

CD

CD

a

ON

co

3 a.
*- P

CO

O

P

fD
i5
fD

g
3

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o

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Forest Floor Thickness (cm)

Appendix D. Mean and standard error for initial root and shoot biomass (g) for stock
type and knife pruning treatments (n = 10).

3.5 -

I ^ B Root Mass
I
i Shoot Mass

3.0 2.5

X

*•»-

Ul illIill I

-s

~s

&

,*• ,*•• , < , , » * • v \ * < *
Treatment

82

APPENDIX E. Anova and Logistic Regression Tables For Data Analyzed in Chapter 4.
D e p e n d e n t V a r : S h o o t t o Root Biomass R a t i o N: 7
M u l t i p l e R: 0 . 8 1 5
S q u a r e d m u l t i p l e R: 0 . 6 6 4
A n a l y s i s of V a r i a n c e
Source Sum-of-Squares
TREATMENT
E r r

df

Mean-Square

^

g

^

3.695

63

q

°r

±

F-ratio
<

Q

QQ1

0.059

D e p e n d e n t V a r : Number of L a t e r a l s Cut i n Upper
M u l t i p l e R: 0 . 5 4 4
S q u a r e d m u l t i p l e R: 0 . 2 9 6
A n a l y s i s of V a r i a n c e
S o u r c e Sum-of - S q u a r e s

P

2Q _1Qg

df

Mean-Square

TREATMENT

70.792

2

35.396

Error

168.364

87

1.935

P l u g N: 90

F-ratio

P

18.290

< 0.001

D e p e n d e n t V a r : R e l a t i v e Growth H e i g h t
N: 310
M u l t i p l e R: 0 . 6 8 9
S q u a r e d m u l t i p l e R: 0 . 4 7 5
A n a l y s i s of V a r i a n c e
Source Sum-of-Squares
SITE
TREATMENT
SITE*TREATMENT
Error

df

2.575
0.969
0.058
3.969

Mean-Square

F-ratio

2.575

192.061

0.162

12.051

0.010

0.724

1
6
6
296

2.838
0.671
0.227
11.856

1
6
6
296

2.838
0.112
0.038
0.040

Dependent Var: AVENEEDLE Length
N: 310
Multiple R: 0.485
Squared multiple R: 0.235
Analysis of Variance

83

< 0.001
0.631

0.013

D e p e n d e n t V a r : R e l a t i v e Growth D i a m e t e r
N: 310
M u l t i p l e R: 0 . 5 1 0
S q u a r e d m u l t i p l e R: 0 . 2 6 0
A n a l y s i s of V a r i a n c e
Source Sum-of-Squares
df M e a n - S q u a r e
SITE
TREATMENT
SITE*TREATMENT
Error

< 0.001

F-ratio

P

70.857
2.792
0.943

< 0.001
0.012
0.465

Source Sum-of-Squares
SITE

F-ratio

1

235.655

66.381

< 0.001

70.020

6

11.670

3.287

0.004

1.007

6

0.168

0.047

1.000

1050.814

296

3.550

SITE*TREATMENT

Response

Mean-Square

235.655

TREATMENT

Error

df

Symmetry

Variable

Number of Response Levels
Model
N= 2 1 8

4

cumulative logit

Response P r o f i l e
Value
1
2
3
4

Sym
1
2
31

4

Effect
Site
AL v s RR
S t o c k Type PSB 4- - 1 5 v s
S t o c k Type PCT 5-- 1 2 v s
S t o c k Type R P 1 4- - 1 5 v s
S t o c k Type RP2 4- - 1 5 v s
S t o c k Type RP3 4- - 1 5 v s
S t o c k _ T y p e RP6 4- - 1 5 v s
S t o c k Type PCT 4- - 1 0 v s
S t o c k _ T y p e PCT 5-- 1 2 v s
S t o c k Type RP1 4- - 1 5 v s
S t o c k Type RP2 4- - 1 5 v s
S t o c k Type RP3 4- - 1 5 v s
S t o c k Type RP6 4- - 1 5 v s
S t o c k J T y p e PSB 4- - 1 5 v s
S t o c k Type PCT 4- - 1 0 v s
S t o c k J T y p e PCT 5- - 1 2 v s
S t o c k J T y p e R P 1 4- - 1 5 v s
S t o c k Type RP2 4- - 1 5 v s
S t o c k J T y p e RP3 4- - 1 5 v s

Frequency
32
55
90
41
Odds
Point
Estimate
1.441
52.567
0.627
6.928
1.147
2.589
1.418
0.019
0.012
0.132
0.022
0.049
0.027
37.075
0.705
0.442
4.887
0.809
1.826

PCT4-10
PCT4-10
PCT4-10
PCT4-10
PCT4-10
PCT4-10
PSB4-15
PSB4-15
PSB4-15
PSB4-15
PSB4-15
PSB4-15
RP6 4 - 1 5
RP6 4 - 1 5
RP6 4 - 1 5
RP6 4 - 1 5
RP6 4 - 1 5
RP6 4 - 1 5

Ratio

Estimates

95% W a l d
Confidence
0.867
17.350
0.243
2.602
0.443
0.995
0.547
0.006
0.004
0.048
0.007
0.017
0.009
12.508
0.272
0.172
1.875
0.315
0.713

Limits
2.397
159.266
1.619
18.446
2.971
6.741
3.676
0.058
0.036
0.362
0.065
0.142
0.080
109.897
1.828
1.138
12.736
2.077
4.677

D e p e n d e n t V a r : RGC TOTAL ROOT Number ( a f t e r 2 1 d a y s ] N: 70
M u l t i p l e R: 0 . 7 7 5
S q u a r e d m u l t i p l e R: 0 . 6 0 1
A n a l y s i s of V a r i a n c e
S o u r c e Sum-- o f - S q u a r e s
df M e a n - S q u a r e
F-ratio
TREATMENT
Error

55735.086

6

9289.181

37074.400

63

588.483

84

15.785

P

< 0.001

Dep V a r : TOTAL ROOT COUNT A f t e r One Growing S e a s o n
M u l t i p l e R: 0 . 7 1 3
S q u a r e d m u l t i p l e R: 0 . 5 0 9
A n a l y s i s of V a r i a n c e
Source Sum--of--Squares
SITE
TREATMENT
SITE*TREATMENT
Error

N: 218

df

Mean-- Square

F-ratio

P

1.637

1

1.637

18.578

< 0..001

16.309

6

2.718

30.850

< 0..001

0.699

6

0.116

1.322

0..249

17.973

204

0.088

D e p . V a r : TOP/TOTAL TOTAL ROOT COUNT A f t e r One Growing S e a s o n
N: 218
M u l t i p l e R: 0 . 7 1 8
S q u a r e d m u l t i p l e R: 0 . 5 1 6
A n a l y s i s of V a r i a n c e
Source Sum-of-Squares

df

Mean-Square

F-ratio

I
< 0..001

SITE

11304..515

1

11304,.515

168..609

TREATMENT

2456..771

6

409,.462

6..107

< 0..001

SITE*TREATMENT

1006..702

6

167..784

2..503

0.,023

13677.303

204

67..046

E r r

°

r

Dep V a r : BOTTOM/TOTAL F r a c t i o n of TOTAL ROOT COUNT
M u l t i p l e R: 0 . 7 3 2
S q u a r e d m u l t i p l e R: 0 . 5 3 5
A n a l y s i s of V a r i a n c e
Source Sum-of-Squares
SITE
TREATMENT
SITE*TREATMENT
Error

df

Mean-Square

N: 218

F-ratio

P

11541 .296

1

11541,.296

73.076

< 0..001

25690 .704

6

4281,.784

27.111

< 0..001

499..089

6

83..181

0.527

0..788

32218..673

204

157..935

85

Dep V a r : TOTAL L a r g e R o o t s (up t o 10)
0.671
S q u a r e d m u l t i p l e R: 0 . 4 5 0
A n a l y s i s of V a r i a n c e

df Mean -Square

Source Sum-•of--Squares
SITE
TREATMENT
SITE*TREATMENT
Error

N: 217

M u l t i p l e R:

F-ratio

166.362

1

166.362

66.191

204.667

6

34.111

13.572

44.341

6

7.390

2 .940

510.211

203

2.513

P
<

0.001

<

0.001
0.009

Dep V a r : TOP/TOTAL LARGE ROOT COUNT
N: 217
M u l t i p l e R: 0 . 6 3 7
S q u a r e d m u l t i p l e R: 0 . 4 0 5
A n a l y s i s of V a r i a n c e
Source Sum-of-Squares
SITE

df

Mean-Square

F-ratio

29196 .080

1

29196 .080

91..497

< 0.001

9682 .899

6

1613 .817

5..058

< 0.001

5201..014

6

866..836

2 .717
.

0.015

64775,.624

203

319..092

TREATMENT
SITE*TREATMENT
Error

Dep V a r : MID/TOTAL LARGE ROOT COUNT
N: 217
M u l t i p l e R: 0 . 4 2 2
S q u a r e d m u l t i p l e R: 0 . 1 7 8
A n a l y s i s of V a r i a n c e
Source Sum-of-Squares

df

Mean-Square

F-ratio

9121.698

1

9121.698

22.611

TREATMENT

5911.774

6

985.296

2.442

0.027

SITE*TREATMENT

2500.962

6

416.827

1.033

0.405

81893.551

203

403.417

E r r

Dep V a r :
R: 0 . 4 3 7
Analysis

Dep

°r

B O T T O M / T O T A L LARGE
Squared multiple
of V a r i a n c e
Source Sum-of-Squares

R O O T COUNT
R:
0.191
df

N:

Mean-Square

217

P
<

0.001

Multiple

F-ratio

P

SITE

5785 .378

1

5785 .378

15,.388

<

0.001

TREATMENT

9909 .823

6

1651 .637

4,.393

<

0.001

SITE*TREATMENT

2297..706

6

382..951

1..019

Error

76323 .204
.

203

375 .976

LARGE

ROOT

M u l t i p l e R: 0 . 6 4 2
S q u a r e d m u l t i p l e R:
A n a l y s i s of V a r i a n c e

Var:

DIRECT

ROOT

COUNT/TOTAL

0.412

86

COUNT

0.414

N:

218

Source Sum-of-Squares

df Mean-Square

F-ratio

SITE

101.691

101.691

5.812

0.017

TREATMENT

2372.183

395.364

22.595

< 0.001

SITE*TREATMENT

40.404

6.734

0.385

0.888

Error

3569.551

17.498

204

Response Variable
TAP ROOT DEVELOPMENT
Number of Response Levels
2
Model Binary logit
N= 218
Response Profile
Ordered
Total
Value
tap
Frequency
1
2

0
1

97
121

Odds R a t i o E s t i m a t e s
Effect
Site
AL vs RR
StockJType PSB4-15 vs PCT4-10
StockJType PCT 5-12 vs PCT4-10
StockJType RP1 4-15 vs PCT4-10
StockJType RP2 4-15 vs PCT4-10
StockJType RP3 4-15 vs PCT4-10
StockJType RP6 4-15 vs PCT4-10
StockJType PCT4-10 vs RP6 4-15
StockJType PSB4-15 vs RP6 4-15
StockJType PCT 5-12 vs RP6 4-15
StockJType RP1 4-15 vs RP6 4-15
StockJType RP2 4-15 vs RP6 4-15
StockJType RP3 4-15 vs RP6 4-15
StockJType PCT 4-10 vs PSB4-15
StockJType PCT 5-12 vs PSB4-15
StockJType RP1 4-15 vs PSB4-15
StockJType RP2 4-15 vs PSB4-15
StockJType RP3 4-15 vs PSB4-15

87

Point
Estimate
0.774
1.287
0.679
0.484
0.266
0.819
0.313
3.197
4.113
2.172
1.546
0.850
2.617
0.777
0.528
0.376
0.207
0.636

95% Wald
Confidence Limits
0.444
1.348
0.464
3.565
0.249
1.854
0.174
1.346
0.090
0.785
0.298
2.250
0.904
0.108
1.106
9.243
1.428
11.846
0.765
6.164
0.535
4.472
0.277
2.603
0.916
7.477
0.281
2.153
0.194
1.434
0.136
1.042
0.070
0.608
0.233
1.740