RESEARCH EXTENSION NOTE
NO 1 – December 2006

How is forest management influencing carbon
storage in sub-boreal forests?

By
Arthur L. Fredeen

The Natural Resources and Environmental Studies Institute
Research Extension Notes (REN) are peer-reviewed publications of
the research findings of NRES Institute members and of graduate
students in the NRES Graduate Program. NRESI Research
Extension Notes are intended to provide an outlet through which
Institute members can make their research findings available to a
non-technical audience.
Dr. Art Fredeen is an Associate Professor with the Ecosystem
Science and Management program and is currently a co-director of
the Natural Resources and Environmental Studies Institute at
UNBC.
The correct citation for this publication is:
Fredeen, A.L. 2006. How is forest management influencing carbon
storage in sub-boreal forests? Natural Resources and Environmental
Studies Institute Research Extension Note No. 1, University of Northern
British Columbia, Prince George, B.C., Canada.
This paper can be downloaded without charge from
http://www.unbc.ca/nres/research_extension_notes.html

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ii

The Natural Resources and Environmental Studies Institute (NRES
Institute) is a formal association of UNBC faculty and affiliates that
promotes integrative research to address natural resource systems
and human uses of the environment, including issues pertinent to
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iii

CONTENTS
Abstract ....................................................................................................... 2
Introduction................................................................................................. 3
Methods....................................................................................................... 4
Measurement of total carbon dioxide (CO2) exchange from a clearcut. 4
Measurement of total forest carbon stocks for the ALRF ...................... 5
Results......................................................................................................... 5
When does a sub-boreal clearcut become a carbon sink?....................... 5
Where is carbon stored in a sub-boreal forest?....................................... 7
How does management influence forest carbon? ................................... 8
Conclusions............................................................................................... 10
References................................................................................................. 11
Further Readings or Resources ................................................................. 12
Acknowledgements................................................................................... 12

1

Research Extension Note No. 1

Abstract
A major question for Kyoto
signatory nations such as Canada is
what role our forests might play in
meeting our greenhouse gas emission
reduction commitments. The most
important greenhouse gas affected by
human activity is carbon dioxide
(CO2). Forests contain high amounts
of carbon, which reflect the net
balance between photosynthetic
fixation of CO2 into tree products primarily cellulose - and the return of
this carbon back to the atmosphere
through respiration and fire. In this
paper I integrate two aspects of my
sub-boreal forest carbon research
program, both conducted at the
Aleza Lake Research Forest (ALRF)
60 km east of Prince George, BC.
Clearcuts are sources of carbon for
two reasons. First, primary forests
contain > 250 tonnes per hectare
while new clearcuts contain <150

Fredeen y Carbon Storage

tonnes per hectare; loss of tree
carbon is immediate and large.
However, even after accounting for
harvesting, clearcuts are net carbon
sources (input CO2 into the
atmosphere) for >8 years after
harvesting while belowground
respiration exceeds photosynthesis.
These carbon losses total 33 tonnes
per hectare over 8 years, despite
gains of 1 to 1.2 tonnes per hectare
per year by the regrowing forest.
Partial cut harvesting conserves the
greatest amount of carbon. In
balance, and after taking into account
different forest management types,
the entire upland region of the ALRF
(6,035 hectares) has been essentially
neutral with respect to carbon over
the past 10 years. Thus, current
forest practices and harvest levels at
the ALRF appear to be sustainable
with respect to carbon.

2

Introduction
Forest harvesting, fire, and
insects are the major disturbance
agents that result in old forests being
converted to young forests across
Canada. In many cases, and
particularly in the aftermath of the
mountain pine bark beetle epidemic,
insect mortality followed by forest
harvesting are the current
disturbance agents in central British
Columbia. With respect to
harvesting, recent figures show that
40% of the wood volume harvested
in Canada comes from British
Columbia, with nearly 16% of this
coming from the Prince George
Forest District alone (NRCAN
2004).
Global warming and climate
change are growing environmental
concerns that are resulting from the
accumulation of greenhouse gases
such as carbon dioxide (CO2) in our
atmosphere. Management of forests
can cause both increases and
decreases in greenhouse gas
accumulation in the atmosphere. A
forest that decreases CO2 in the
atmosphere is termed a carbon sink,
while one that increases it is termed
a carbon source.
On the carbon source side,
deforestation explains about one
third of the rise of CO2 in the
industrialized period (1850 to
present), mostly because mature and
particularly old forests contain large
stores of carbon that gets locked up
in live and dead wood for long
periods of time (IPCC 2000). This
carbon is released to the atmosphere
when short-lived forest products are
decomposed in land-fills. In
balance, forests (because of net
deforestation globally) still

3

contribute 20% of the increase in
CO2 concentrations globally, though
much of this is occuring in the
tropics and not in the boreal forests
to the north. Finally, clearcuts are a
source of CO2 for some period of
time following harvest, when losses
of CO2 due to respiration exceed that
gained through photosynthesis. The
timing of this transition from carbon
source to carbon sink for clearcuts
has until recently been largely
unknown.
On the carbon sink side,
regrowing forests (reforestation) can
potentially recapture all of this lost
forest carbon through photosynthesis
(fixation of CO2) if harvest rotations
are long enough to permit full
recovery of forest carbon stocks.
Afforestation, the growth of trees on
land that did not previously contain
trees, is of greater significance, in
that genuine gains in carbon can be
made over non-forested land
surfaces. However, afforestation is
of limited applicability to landscapes
already dominated by forests such as
those in central British Columbia.
In this paper, I summarize
two different experimental
approaches that I and collaborators
have taken to understand how forest
carbon storage is influenced by
forest management in central British
Columbia. First, I examine the net
uptake of CO2 in a sub-boreal
clearcut over multiple years to
understand when re-planted clearcuts
become net sinks for CO2 after
harvesting (Pypker and Fredeen
2002a, 2002b; Fredeen et al. 2006).
Second, I examine how much forest
carbon occurs both aboveground in
the trees, woody debris and litter,
and below ground in the roots and
soil across ecosystem, age-class and
Research Extension Note No. 1

management boundaries in subboreal forests similar to the clearcutstudy site (Fredeen et al. 2005,
Janzen 2006). Taken together, these
experimental approaches have
helped to quantify the way in which
forest management activities have
affected carbon storage in sub-boreal
forests of British Columbia.

Methods
All of the following
studies were conducted at the
Aleza Lake Research forest
(ALRF) ~60km north-east of
Prince George. (Figure 1).

Measurement of total
carbon dioxide (CO2)
exchange from a
clearcut
To determine when a
clearcut becomes a carbon
sink, a combination of two
basic approaches to measure
clearcut CO2 exchange were
used: 1) component CO2exchanges (respiration and
photosynthesis) in the
clearcut were measured using
a portable gas-exchange
instrument (Li6200) and then
multiple regression models
were created relating CO2-

Figure 1. The Aleza Lake Research Forest (ALRF) is the oldest
experimental forest in British Columbia.* The ALRF is situated within
the central plateau of British Columbia between the northern Rocky
Mountains to the east and the coastal mountains to the west. The ALRF
is classified as (SBSwk1: wet and cool subzone of the sub-boreal spruce
bioegeoclimatic zone) with forests dominated by interior spruce (Picea
glauca x engelmannii) and subalpine fir (Abies lasiocarpa). Mean annual
precipitation at the ALRF is 930 mm (one third as snow) and the mean
annual temperature is 3°C.
* Figure courtesy of D. Janzen, M.Sc. thesis.

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4

exchange to microclimate
variables to determine the
overall CO2 exchange for the
clearcut, and 2) total CO2
exchange for an entire
clearcut were determined in
an integrated measurement
using either Bowen-ratio
Energy Balance (BREB) or
Eddy Covariance (EC)
approaches. These methods,
approaches and equipment
are more fully described
elsewhere (Pypker and
Fredeen 2002a, 2002b;
Fredeen et al. 2006). The
84.15 ha clearcut (harvested
in 1994) is located in the
southwest corner of the
ALRF and its CO2 fluxes
measured in 1999 (year 5
after harvest), 2000 (year 6),
2002 (year 8) and 2004 (year
10).
Measurement of total
forest carbon stocks for
the ALRF
To quantify all of the
important forest carbon
stocks within the upland
conifer-dominated regions of
the ALRF, we randomly
located and intensively
sampled carbon in 147 x 400
m2 plots across 6,035
hectares of the ALRF from
2003 to 2005, excluding all
riparian and flood plain
associated with the Bowron
river, lakes, streams,
roadways, and bogs. All
plot-level tree, shrub, herb,
woody debris, litter, and soil
carbon to 1 meter in depth
were sampled and their

5

carbon determined either
directly using a carbon
analyzer or indirectly by
using published carbon
contents and relationships
between dimensional
properties such as length,
height and diameter and
mass.
Aboveground and
belowground carbon stocks
were summed for each plot
and extrapolated to the
landscape level using satellite
imagery of the ALRF
(Landsat) from 1992 to 2003,
forest inventory data and
Geographic Information
Systems (GIS). For more
details on carbon stock
sampling and modeling
procedures, see Fredeen et al.
(2005), Janzen (2006), and
Janzen et al. (2006).

Results
When does a sub-boreal
clearcut become a
carbon sink?
There was a
considerable amount of yearto-year variation of annual
losses and gains of CO2 from
the spruce-planted clearcut at
the ALRF. Never-the-less,
the linear regression
relationship between net CO2
exchange and time since
clearcutting was relatively
strong (R2 = 0.67) suggesting
that the clearcut appears to
transition from CO2 source to
CO2 sink at between 8 and 10
years (8.3 y) after clearcut
harvesting (Figure 2). The
Research Extension Note No. 1

Figure 2. Transtion from carbon source to carbon sink in a clearcut at the
Aleza Lake Research Forest 60 km east of Prince George, British
Columbia. Data are indicated for years 5,6, 8, and 10 after clearcut
harvesting. A linear regression line was fit to the relationship of annual
forest-level net CO2 exchange: NCE (tonnes C ha-1 y-1) versus clearcut
age (years): NCE = 0.972 * (clearcut age) - 8.047; R2 = 0.67
clearcut contributed an
average of 3.2 tonnes of
carbon per hectare per year in
years 5 and 6, and removed
an average of 1.2 tonnes of
carbon per hectare per year in
years 8 and 10 after
harvesting (Figure 2).
Immediately after
harvest, the clearcut would be
expected to be a source for
carbon equivalent to the
belowground respiration rate.
The mean belowground
respiration rates for clearcuts
at the ALRF in a previous
study were found to be
relatively consistent from
between 0 and 10 years after
Fredeen y Carbon Storage

clearcutting with a mean of
8.7 tonnes of carbon per
hectare per year (Fredeen et
al. 2006), a value close to the
'y'-intercept of -8.1 tonnes of
carbon per hectare per year
(Figure 2). These data
provide tangible support for
the general principle that
clearcuts are initially carbon
sources after harvesting and
only later become net carbon
sinks when photosynthesis by
the vegetation exceeds
belowground respiration.
The total carbon lost after
clearcutting, again using the
simple linear relationship
shown in Figure 2, would be
33 tonnes of carbon per

6

hectare, which means that the
clearcut would not regain
these initial net losses of
carbon until year 16.
The question of how
much carbon is taken up by
sub-boreal clearcuts was also
addressed by another method
whereby the change in total
permanent (biomass) carbon
stocks in clearcuts of various
ages were examined through
a combination of remote
sensing and carbon-stock
measurements (Janzen 2006,
Janzen et al. 2006). These
measurements indicate that
10 to 20 year-old clearcuts in
the ALRF accumulate carbon
at a rate of approximately 1.1
tonnes of carbon per hectare

per year, a value nearly
identical to either the average
carbon sink for years 8 and
10 (1.2 tonnes of carbon per
hectare per year; Figure 2) or
the slope of the linear
regression line for annual
carbon fluxes (1.0 tonnes of
carbon per hectare per year;
Figure 2).
Where is carbon stored
in a sub-boreal forest?
The greatest stores of carbon
in sub-boreal forests, and in
fact most forest types, are
found in the oldest stands.
This was the case with subboreal forests at the ALRF
(Figure 3).

Figure 3. Quantities of measured carbon (tonnes of carbon per hectare)
contained in large tree, understory vegetation and soil to a depth of 50 cm
within forest stands of different age ranges across the Aleza Lake
Research Forest.

7

Research Extension Note No. 1

We consistently observed
increases in total forest
carbon with age even
between the oldest age
classes. Not surprising was
that tree carbon, along with
lesser contributions from
forest floor and woody
debris, was the main
contributor to the increase in
forest carbon with age
(Figure 3). By contrast, soil
carbon was relatively stable
with increasing forest age,
representing over half of the
carbon in young stands (0 to
20 years old) and around one
third of total ecosystem
carbon in the oldest stands
(>175 years old).
How does management
influence forest carbon?
A particular problem
encountered in assessing the
way in which forest
management influences forest
carbon was that forest
management, including
things such as: harvesting
method, site preparation
following harvesting,
regeneration approach (e.g.
natural versus planting),
stocking density, type and
species, have all varied
considerably over time. This
presented some unique
challenges to making
comparisons between
management history types
with respect to carbon
accumulation because no
aspect of management could
be directly compared to
another at any point in time.
Fredeen y Carbon Storage

One such comparison that I
had hoped to be able to make
was between partial cutting
and clearcutting, since both
types of harvesting have
occurred at the ALRF, and
both are harvesting systems
still in use today. However,
most of the partial cutting
was done pre-1980 and, in
operational terms, it varied
considerably, from stripcutting to various forms of
diameter-limit logging. Even
clearcutting and the
subsequent post-harvest
activities have varied
tremendously over the last
few decades. Thus, while
detailed comparisons were
not possible, we were able to
contrast the way in which
broad classes of forest
management from 1992 to
2003 affected carbon storage
today by way of remote
sensing and modeling of C
stocks using Landsat imagery
spanning this 11 year period
(Table 1).
Over the past 11 years, the
ALRF study area has
contained approximately 670
kilotonnes of biomass and
woody debris carbon (Janzen
2006). The ALRF is
essentially neutral with
respect to carbon
accumulation between 1992
and 2003, registering a small
loss (not significant) of
carbon over this 11 year
interval (-8.7 ±10.6
kilotonnes of carbon) after
weighting the four

8

Table 1. Land area (hectares) and changes in biomass + woody debris
carbon stocks from 1992 to 2003 for 4 forest management classes within
the Aleza Lake Research Forest: (1) new clearcuts (NCC: harvested
between 1992 and 2003) (2) old clearcuts (OCC: harvested before 1992),
3) old partial-cuts (OPC: harvested prior to 1992), and 4) undisturbed
primary forest (UPF). Positive values indicate a gain in carbon from 1992
to 2003.*
Average change in carbon from 1992 to
2003 (tonnes ha-1)

Class

Area
(hectares)

Biomass

Woody
Debris

Biomass +
Woody Debris

Total change in
carbon from
1992 to 2003
(kilotonnes)
Biomass +
Woody Debris

NCC

323

-121.2 ± 7.5

-2.2 ± 2.5

-123.5 ± 8.0

-39.9 ± 2.6

OCC

1507

12.1 ± 2.8

-1.4 ± 0.9

10.7 ± 2.9

16.1 ± 4.4

OPC

1411

-0.2 ± 3.7

0.6 ± 1.2

0.4 ± 3.9

0.6 ± 5.5

UHF

2794

4.6 ± 2.5

0.6 ± 0.8

5.2 ± 2.7

14.5 ± 7.5

Total

6,035

-8.7 ± 10.6

*Adapted from D. Janzen, 2006. M.Sc. thesis, UNBC.

management classes by their
respective areal extent in the
ALRF (Table 1). However,
many forest management
types are combined into this
forest-level carbon change,
all with different carbon
outcomes. First, both new
and old clearcuts combined
represented net losses of
carbon. New clearcuts
(NCC), here defined as those
less than 11 years since
harvest, registered large
carbon losses (Table 1),
primarily because of the
accounting procedures used
whereby losses of primary
forest carbon resulting from
harvesting were attributed
solely to new clearcuts. By
contrast, 'old' clearcuts
(OCC: greater than 11 years

9

old) accumulated carbon at
between 1.0 and 1.2 tonnes of
carbon per hectare per year
(see Table 1 and Figure 2).
Second, older forest stands
recovering form partialcutting (OPC) have high
carbon stocks, in some cases
as high as unharvested
primary forest (Janzen 2006),
but they appear to be
relatively neutral with respect
to present day carbon uptake
(Table 1). This result was
unexpected given the
accumulation of carbon
observed for unharvested
forests (UHF: ~ 0.5 tonnes of
carbon per hectare per year),
which were essentially
primary, mature to oldgrowth forest stands. It is not
surprising that older partial
Research Extension Note No. 1

cuts would be carbon neutral
relative to clearcuts, since
they are of greater age than
clearcuts in the ALRF, and
even after harvest, would
have had a high composition
of already mature trees.
However, it is puzzling that
by contrast, unharvested
stands were accumulating
carbon when they might have
been expected to be more
stable with respect to carbon
than old partial cuts.

Conclusions
There is no question that
clearcuts result in enormous
carbon losses, particularly in
the first 8 to 10 years after
harvest, and that these losses
could be minimized by

Fredeen y Carbon Storage

partial-cutting. However, it
remains to be determined
how carbon stocks are
affected by these different
harvesting methods over the
longer term. A move to
shorter forest harvesting
rotation ages will reduce
forest carbon storage but
greater longevity of forest
products, for example, could
at least partially offset lower
spatially-averaged carbon
stocks. While carbon storage
is only one forest stewardship
concern, it may well be an
important one, particularly in
boreal nations such as
Canada where climate change
(warming) is occurring at
twice the rate of the global
average.

10

References
Fredeen, A.L., Bois, C.H., Janzen, D.T., P.T. Sanborn 2005. Comparison
of coniferous stocks between old-growth and young second-growth
forests on two soil types in central British Columbia, Canada.
Canadian Journal of Forest Research 35: 1411-1421.
Fredeen, A.L., Waughtal, J.D., T.G. Pypker 2007. When do replanted
sub-boreal clearcuts become net sinks for CO2? Forest Ecology and
Mangement 239: 210-216.
Intergovernmental Panel on Climate Change (IPCC). 2000. Land use,
Land-Use Change, and Forestry. A special report of the
Intergovernmental Panel on Climate Change. WMO/UNEP. Available
at: http://www.ipcc.ch/ [Accessed on 5 December 2006].
Janzen, D.T. 2006. The impacts of forest management activities on
carbon stocks and sequestration in the Aleza Lake Research Forest.
M.Sc. Thesis. University of Northern British Columbia, Prince
George, British Columbia, Canada.
Janzen, D.T., Fredeen, A.L., R.D. Wheate. 2006. Radiometric correction
techniques and accuracy assessment for Landsat TM data in remote
forested regions. Canadian Journal of Remote Sensing 32: 330-340.
Natural Resources Canada 2004. The State of Canada’s Forests: 2003–
2004 [online]. Available at: http://www.nrcan.gc.ca/cfsscf/national/what-quoi/sof/latest_e.html [Accessed on 5 December
2006].
Pypker, T.G., A.L. Fredeen 2002a. The growing season carbon balance
of a sub-boreal clearcut 5 years after harvest using two independent
approaches to measure ecosystem CO2 flux. Canadian Journal of
Forest Research 32: 852-862.
Pypker, T.G., A.L. Fredeen 2002b. Ecosystem CO2 flux over two
growing seasons for a sub-Boreal clearcut 5 and 6 years after harvest.
Agricultural and Forest Meteorology 14:15-30.
Pypker, T.G., A.L. Fredeen 2003. Below ground CO2 efflux from cut
blocks of varying ages in sub boreal British Columbia. Forest
Ecology and Management 172: 249-259.
Waughtal, J.D. 2003. Quantification of carbon pools and fluxes in
relation to land-use in sub-boreal British Columbia. M.Sc. Thesis.
University of Northern British Columbia, Prince George, British
Columbia, Canada.

11

Research Extension Note No. 1

Further Readings or Resources
Prentice et al. 2001. The carbon cycle and atmospheric carbon dioxide.
In Climate Change 2001: The Scientific Basis. Contribution of
Working Group I to the Third Assessment Report of the
Intergovernmental Panel on Climate Change. Cambridge University
Press, Cambridge, UK and New York, NY, USA, 881 pp.
http://www.ipcc.ch/
Thornley, J.H.M., and Cannell, M.G.R. 2000. Managing forests for wood
yield and carbon storage: a theoretical study. Tree Physiology 20:
477-484.
Smithwick, E.A.H., et al. 2002. Potential upper bounds of carbon stores
in forests of the Pacific Northwest. Ecological Applications. 12:
1303-1317.

Acknowledgements
Claudette Bois, Darren Janzen, and Drs. Paul Sanborn and Roger Wheate
were the author's primary collaborators in measuring and modelling
carbon stocks. Jennifer Waughtal and Dr. Tom Pypker were the author's
primary collaborators for the measurement of clearcut CO2 fluxes. This
research was funded by the Canadian Foundation for Climate and
Atomspheric Sciences (CFCAS), the National Sciences and Engineering
Research Council (NSERC) of Canada, and Human Resources
Development Canada. The author is grateful for the assistance of the
manager and staff of the Aleza Lake Research Forest.

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