Download Studies specific to Boreal forests

The Influence of Land Use Change on Landscape Pattern and Carbon Cycling
in Boreal Forests:
A Working Annotated Bibliography
Date Started: October 24, 2002
Updated: November 19, 2002, November 24, 2002
Last Updated: 5 December 2002
I. General background articles:
The influence of fire on boreal forests:
Arseneault, D. 2001. Impact of fire behavior on postfire forest development in a homogenous boreal
landscape. Can. J. For. Res. 31: 1367-1374.
Goldammer, JG, and Furyaev, VV. 1996. Fire in ecosystems of boreal Eurasia: Ecological impacts
and links to the global system. In: Fire in Ecosystems of Boreal Eurasia. pp. 1-20. Kluwer.
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General background and statistics on fires in boreal forests, with the focus being on Eurasia.
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“…lightning-ignited fire is the most important factor controlling forest age structure, species
composition and physiognomy, shaping landscape diversity, and influencing energy flows and
biogeochemical cycles.
Small and large fires of varying intensity have different effects on the ecosystem. High-intensity
fires lead to the replacement of forest stands by new successional sequences… Low-intensity surface
fires favor the selection of fire-tolerant trees such as pines (Pinus spp.) and larches (Larix spp.) and
may repeatedly occur within the lifespan of a forest stand.” p 2
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“In Eurasia fire has for a long time been an important tool for land clearing (conversion of boreal
forest), silviculture (site preparation and improvement, species selection) and in maintaining
agricultural systems, e.g. swidden agriculture, pastoralism, and hunting societies (citations)…In the
early 20th century, the intensity of fire use in the agricultural sector began to decrease since most of the
deforestation had already been accomplished for agriculture…Humans are still the major source of
wildland fires; only 15% of the recorded fires in the Russian Federation are caused by lightning…” p 3
 I don’t think this is true in Canada. Also, note that most fires in Siberia and the Russian Far
East are actually not reported because they are far from settled areas, so there is probably a higher
incidence of lightning-ignited fires than 15%. G&F discuss this, also.
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“In recent years wildfires have been more or less eliminated in the Nordic countries (Norway, Sweden,
Finland; citation).” p 4
This emphasizes the relatively longer and more intensive history of European (?) land use in
Europe as opposed to in Canada.
Table 1 shows annual estimated burned areas in world boreal forests; boreal Fennoscandia and China
are relatively low compared to N. America and Eurasia. p 5
Boreal fires seem to emit higher concentrations of heavy greenhouse gas and ozone-depleting
compounds (CO, CH4, CH3Br, CH3Cl) than tropical and subtropical savanna/chaparral because of
incomplete combustion from smoldering surface fires.
Because of future climate warming, “an increase in the length of the fire season would lead to a higher
occurrence of large, high-intensity wildfires” (p 7). To me, this strongly suggests that fire suppression
will only become more difficult in the future. However…
“Over the longer term [Kasischke et al. (1995)] expect flammability to decrease for the above-ground
biomass because of the long-term shift towards less flammable deciduous trees. In the near term the
surface fuels (ground layer) would become drier and more flammable, thus increasing the overall fire
risk of forests in the transition to the new equilibrium.” Kasischke et al predict 20-50% increase in
annual area burned in the next 50-100 yr, leading to a potential net carbon loss of 46-54 Pg to the
atmosphere.
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“Traditional forestry practices and low-impact and sustainable use of non-wood forest products in
boreal Eurasia are being subjected to dramatic changes which are stimulated by increasing national and
international demands for boreal forest products. This has resulted in the widespread use of heavy
machinery, large-scale clearcuts, and thereby in the alteration of the fuel complexes. Many clearcut
areas are reportedly not regenerating into forest but are rather degrading into grass steppes
which may become subjected to short-return interval fires. The opening of formerly closed remote
forests by roads and subsequent human interferences bring new ignition risks.” p 9
Prescribed burning was used in Fennoscandia (starting in?) in the 18th and 19th centuries “for
improving grazing in forests, for slash and burn agriculture, and for forest regeneration” (p 10), and in
Siberia in the 1950s.
II. Articles about Historic (Pre-industrial era) land uses of boreal forests, about Historic (Preindustrial-era) landscape structure, and processes (i.e. fire and logging history)
Ostlund, L., O. Zackrisson, and G. Hornberg. 2002. Trees on the border between nature and culture:
culturally modified trees in boreal Sweeden. Environmental History 7(1): 48-68.
This study focuses on the culturally modified trees (CMTs), meaning trees that people have scarred, shaped
and used for cultural purposes. The paper is slanted toward an environmental history audience; the paper’s
main argument is that these CMTs serve as a living archive that can tell much about the historic
relationship between people and forests.
This paper is useful to our study in that it provides a framework to discuss historic forest land uses in this
area. The authors introduce the distinction between pre-industrial and industrial era land uses (p. 49). I
think we may want to adopt this distinction in our paper.
In boreal Sweden, people have resided since the Mesolithicum (10,200- 5,400 B.P.). According to several
pollen studies, human activities apparently did not alter forest structure (at the landscape scale) during the
entire Hollocene. The effects of human activities on forests were limited to the local scale, through fire, for
example.
Agricultural Cultivation Period: About 2,000 years B.P., people began to establish restricted cultivations.
These activities demarcate the “first major detectable impact on local forest structure” in the boreal region
of Sweden. People cleared small fields in which they grew cereals and raised cattle in the forest. “The
population density was often less than one person per square kilometer, and villages and farms were
situated far apart.” The authors, thus conclude that it seems probable that forest structure fore most of the
post-glacial period was primarily influenced by natural disturbances like climate and fire. During this era,
people drew upon large forest areas to collect the variety of necessary specific resources, such as winter
fodder, wood, and fish. People looked to forests to serve multiple uses.
During this era, one of the primary forest uses was as rangeland. Farmer settlers killed standing trees by
ringbarking (girdling?) them, which served the two-fold purpose of opening up the forest to allow
herbaceous species to grow, and providing fire wood.
Industrial Period: The industrial era (i.e. of the past 100 years) introduced major changes in the use of the
boreal forests (and on forest structure). As Scandinavia industrialized, forests uses shifted from multipleuse to single-use. The use of forests as a source of pulpwood and lumber superceded agricultural and forage
uses. This shift was driven by the development of the market economy: markets for lumber and pulp
developed, which the developing Sweden strove to meet.
Axelsson, A.L. and L. Ostlund. 2001. Retrospective gap analysis in a Swedish boreal forest landscape
using historical data. Forest Ecology and Management. Volume? (2001): 1-14.
Axelsson, A.L. 2001. Old Tree in Northern Sweden-An historical analysis. Dissertation chapter in
A.L. Axelsson, Forest Landscape Change in Boreal Sweden 1850-2000: A multi-scale approach.
Swedish University of Agricultural Sciences.
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Storaunet, K.O., J. Rolstad, and R. Groven. 2000. Reconstructing 100-150 years of logging history in
coastal spruce forest (Picea abies) with special conservation values in central Norway. Scand. J. of
For. Research. 15: 591-604.
Lehtonen, H. and T. Kolstrom, 2000. Forest fire history in Viena Karelia, Russia. Scand. J. of Forest
Research. 15: 585-590.
III. Articles about the influence of Historic land uses (and Land Use Change) on Landscape Pattern
Ostlund, L., O. Zackrisson, and A.-L. Axelsson. 1997. The history and transformation of a
Scandinavian boreal forest landscape since the 19th century. Canadian J. of Forest Research. 27:
1198-1206.
Axelsson, A.-L., L. Ostlund, and E. Hellberg. 2001. Use of retrospective analysis of historical records
to assess changes in deciduous forests of boreal Sweden: 1870s –1999. Dissertation chapter in A.L.
Axelsson, Forest Landscape Change in Boreal Sweden 1850-2000: A multi-scale approach. Swedish
University of Agricultural Sciences.
Johnson, EA and others. 1990. The influence of man and climate on fire frequency of the Interior
Wet Belt forest, British Columbia. J. of Ecology. 78: 403-412.
This paper doesn’t tell us much about the effects of land use on boreal forest pattern. But, it does tell us
something about the way that human presence has affected fire frequency in one boreal forest in Canada,
the forest in Glacier National Park, which does have implications for forest pattern.
The major finding is that human presence has not significantly affected fire frequency in the forests of
Glacier National Park. This, to me, is a surprising finding. I would think that both the creation of the
Canadian Pacific Railroad (and other railroads) and fire suppression would have altered fire frequency.
Johnson and colleagues’ point is fire frequency at the landscape scale is a measure of both recurrence
interval and area burned. They found that the fires started by human activities are quite small relative to the
size of typical wildfires, and thus, human-initiated fires have had not significantly increased fire frequency
(see p. 409). “In order to increase the fire frequency about the natural fire regime, Europeans would have
had to start fires which consistently burned significant areas during those same periods [of cirtical fire
weather]” (p. 411). Conversely, in order to “reduce the fire frequency below that of the natural fire regime,
fires must be suppressed [at times of critical fire weather]” (p. 411). But, the authors argue, climate, in the
form of a surface high pressure system that blocks the flow of moist air, creating very dry conditions,
overrides any affect that fire suppression efforts can bring about.
Therefore, in the Glacier National Park forest system, which is strongly driven by climate, human presence
has not significantly altered fire frequency. This case study appears to represent one case where abiotic
factors override human activities in influencing landscape pattern. The strong influence of climate on fire
frequency appears to limit the influence of anthropogenic activity (i.e. land use) on fire frequency.
Weir, J. and EA Johnson. 1998. Effects of escaped settlement fires and logging on forest composition
in the mixedwood boreal forest. Canadian J. of For. Res. 28:459-467
I have only skimmed this article. It looks very useful to our study, however! Applications to our study: This
investigation shows a case in which past land use has influenced patterns of vegetative composition in
boreal forests.
This study concludes that the combination of logging and escaped fires from agricultural settlements south
of the study area (Price Albert National Park, Saskatchewan), changed the vegetative composition of the
forest in the early twentieth century. Fifty years after these disturbances, their effects on the vegetation
persist. Logging and the introduction of a short fire recurrence interval (i.e. less than 20 years) have
“caused a white-spruce-dominated mixed wood forest to convert to an aspen-dominated mixedwood forest.
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Furthermore, when one episode of selective logging for mature white spruce is introduced, the magnitude
of this change increases. Both increased fire frequency and selective logging are associated with
agricultural settlement of the forested region south of the study area” (p. 466). The authors predict that
another fifty years will be required for the surviving individuals (remnant populations) of species that
experienced substantial decline to recolonize the area.
Weir, J.M. and others. 2000. Fire frequency and the spatial age mosaic of the mixed-wood boreal
forest in western Canada. Ecological Applications 10(4): 1162-1177.
Argument/ slant: Weir and others argue that this research is important because of its applications
to ecosystem management. “If the goal of ecosystem management is to maintain the spatial heterogeneity
of the age mosaic pattern of the forested landscape, it is obviously essential to know what that mosaic
pattern actually is and what factors cause variation in the spatial heterogeneity” (Weir and others 2000:
1163). They conclude that species composition and stand ages are rarely, if ever, likely to be in equilibrium
with their disturbance regime, where equilibrium is defined “as that occurring during periods when the fire
cycle is constant.” Their reasoning is that a) the fire cycle has changed significantly (e.g. due to climate
change); b) periods characterized by a constant fire cycle interval are often shorter than the longevity of
tree species; c) “the spatial mosaic of stand ages is a reflection of these past fire cycles”(p. 1175-76).
The authors argue that two factors shape the mosaic pattern of stand types:
1. Community vegetative types. Hillslope geomorphology, which includes hillslope position and surficial
geology, in turn affects moisture and nutrient gradients. These gradients influence the vegetation pattern in
terms of species presence. This factor is beyond the scope of the research presented in this paper; the
authors present this factor in the introduction only.
2. Stand ages. Wildfire shapes the pattern of stand ages. More recent fires overburn sites that previously
burned, creating a mosaic of patches that reflect the variation in time since burning. This paper does
address this factor.
Hypotheses (p. 1163):
1. The human-set fires used to clear the forests for settlement may have spread and thus increased the
fire frequency of the study area.
2. The isolation of the study area from continuous forest after the completion of forest clearance for
agriculture in the surrounding areas caused a decrease in fire frequency.
Research Design:
The authors investigated the timing and rate of forest clearance in the surrounding areas, then assessed the
direction of spread of large fires in the region to see how/ if a change in fire frequency relates to land use
change.
The creation of a time-since-fire map enabled the investigators to investigate the effect of fire history on
forest vegetative pattern.
Results
Fire Frequency Analysis:
This investigation divided the study area into two parts—the northern zone, which is forested (and
is currently within Prince Albert National Park), and the southern zone, which experienced agricultural land
use, esp. in the early twentieth century.
In the northern zone, fire frequency changed significantly through time (p < 0.0005). Prior to
1890, the fire cycle was 15 yr (95% CI = 10—35 yr); between 1890 and 1945, the fire cycle was 75 yr (CI
= 45 – 150 yr); since 1945, the fire cycle is much larger, 1,745 yr (CI = 285- 127,225 yr). In the southern
zone however, the fire cycle did not change significantly over time (p > 0.05). Prior to 1945, the fire cycle
was 25 yr (CI = 15- 40 yr); after 1945, the fire cycle was 645 yr (CI = 200- 4270 yr). While the estimates of
fire cycles in the southern agricultural land use zone are different, the difference is not significant at the
0.05 level.
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Land use change
This study investigated whether forest land conversion rates per homestead differed during four periods of
settlement, Interval 1: 1930-1940, 2: 1920-1930; 3: 1908-1920; 4: before 1908.
The investigators found that conversion rates differed significantly between the earliest three periods;
however, the rate did not vary between 1920-30 and 1930-40. The overall conversion rate between 1890
and 1940 was 5.09 acres per year.
--Settlement-caused fires burned into the park more frequently between 1927 and 1940 than after 1940.
This gives some support to Hyp. 1.
--70% of the large wildfires that burned in the mixed-wood boreal forest if Saskatchewan between 1980
and 1992 spread in a northernly direction, and these fires were larger than those that spread to the south.
Effects of land use change on fire frequency:
Fire cycle interval increased significantly in the northern zone (the national park), whereas it did not in the
southern zone (the agricultural land use area). The authors attribute the change in the north to the cessation
of the Little Ice Age. During the ice age, persistent blocking high pressure zones characterized the climate,
which are strongly associated with the ignition of large wildfires (p. 1173). The authors use this
relationship to explain why fire cycles were so small during the Little Ice Age, and why they increased in
the northern zone after 1890, when the ice age ended. In the southern zone however, fire cycles did not
change significantly (i.e. they didn’t increase, like they did in the northern zone). The authors attribute this
distinction between northern and southern fire cycles after 1890 to land use of forest clearance for
agriculture that occurred in the south.
[Interesting note: “Consequently, the fringe [south of the National Park] is also the site of the fairly recent
shift in landuse (sic.) from a wildland landscape (forest) to a cultural landscape (agriculture). The creation
of this cultural landscape and its impact on fire, one of the major disturbances in the boreal forest, ahs
probably followed a similar patterns along its entire southern fringe.” (p. 1174).]
Effects of change in fire frequency (in the northern zone) on forest patterns:
1. Effects on patches of tree size, shape, and age (p. 1174): In the forested northern zone of the
Prince Albert NP, fire cycles became longer after 1890. Thus, the remnants of past large fires
disappear more slowly than those in the southern agricultural zone, where fire frequency did not
change from 1890, so is still relatively short. Furthermore, the polygon/ site of a wildfire at t 1
would bear the imprint of overburing by later fire(s) (t n). As a result, the patches (polygons) in the
forested northern zone are smaller, more circular, and more compact, and of an older age than
those of the southern zone. For more details, see p. 1174, column 2, paragraph 2.
2. Effects on patterns of vegetative composition (p. 1174-75): “Changes in the fire cycle are
expected to have implications for the species composition of the forest. Short fire cycles tend to
favor species with either short prereproductive periods (such as Pinus banksiana) or vegetative
reproduction (such as Populus tremuloides) in those sites suitable for these species.” (p. 1174).
“Bridge and Johnson (2000) showed that the southern half of the park has more Populus
tremuloides and less Picea glauca than expected by the distribution of moisture-nutrient gradients.
Weir and Johnson (1998) explained this difference between expected and observed stand
composition pattern as a result of the combined impacts of logging and frequent fires. As we have
shown, these fires were largely due to the northward spread of debris fries set during agricultural
clearing in the settlement areas surrounding the south half of the park.” (p. 1175)
These authors dispute the assertion that closed-canopy conifer forests of North America are accurately
characterized by a mosaic pattern of smaller patches of young growth within a matrix of old growth.
Rather, they have seen the opposite pattern: “smaller patches of older forest embedded within a matrix of
older forest.” They cite fire cycle intervals to explain this pattern. For the forest matrix to consist of old
growth, a region would have to experience an absence of fire for a very long time (> 200 yr (approaching
the upper end of the lifespan of typical arboreal species), with only a few small fires, therefore, a “very
long fire cycle.” But, “all of the time-since-fire studies of closed canopy conifer forest of North America
have shown very short fire cycles prior to the end of the Little Ice Age (which occurred at the end of the
19th century)” [whose studies are they talking about? Theirs? Others???]
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IV. Articles about the Influence of Current Land Uses, especially industrial Forestry, on Forest
Pattern
And, simulation model projections of boreal forest change
Axelsson, A.L, L. Ostlund, and E. Hellberg. 2001. Use of retrospective analysis of historical records
to assess changes in deciduous forests of boreal Sweden: 1970s-1999. In: A.L. Axelsson. Forest
Landscape Change in Boreal Sweden 1850-2000: A multi-scale approach. Doctoral Thesis. Swedish
University of Agricultural Sciences.
Large changes in the patterns and abundance of deciduous trees in boreal forests of Sweden have occurred.
These are due to “complex interactions between fire disturbance, fire suppression, logging, and
silviculture.” Prior to fire suppression, previous fire activity primarily influenced the presence of deciduous
trees; where fire had occurred, broad-leafed trees were likely to grow. Later, selective logging disturbed
successional pathways and favored regeneration of deciduous species (and expansion in their abundance?).
During the twentieth century, steps were taken to curb the extent of deciduous species: people girdled,
thinned, and applied herbicide to birch (silver birch (Betula pendula Roth.) and hairy birch (B. Pubescens
Ehrh.) and aspen because they were perceived as serious threats to the success of coniferous plantations.
Where deciduous trees exist, they mainly occur in young stands.
Changes in Forest landscape structure: Prior to the early 1900s, a multi-aged forest containing large
coniferous trees characterized most stands. Coniferous species dominated most stands while deciduousdominated forest grew only in small stands.
At a landscape scale, on mesic sites, multi-aged stands of scots pine (Pinus silvestris L.) dominated the
forest matrix, which were interspersed with patches of deciduous trees (Axelsson and Ostlund 2001). What
was the process that drove this pattern? A fire-dominated disturbance regime and successional processes
were primary shapers of the landscape pattern.
“Since the 1920s, the total volume of deciduous trees in Sweden has increased (Berg et al. 1996) and today
14% of the total timber volume in Northern Sweden consist of deciduous trees (Anon 2000)” (p. 3). But,
coniferous tree volume has increased more in absolute numbers than deciduous tree volume, so the relative
proportion of volume of deciduous trees has decreased. The proportion of birch trees less than 20 cm DBH
exceeds 80% of the birch volume (Stener 1998).
(Note that the majority of deciduous forest has been found on land that has been used for agriculture in the
past (Mikusinski and Angelstam 1999).
Shifting forest uses: Use of deciduous species has changed radically in the past 200 years. Initially they
were perceived as a valuable resource (Slotte 1997, in Axelsson et al. 2001); later (in the twentieth
century?), they were considered a hindrance to conifer management.
He, H.S., Z. Hao, D.R. Larsen, L. Dai, Y. Hu, and Y. Chang. 2002. A simulation study of landscape
scale forest succession in northeastern China. Ecological Modelling 156 (Issues 2-3): 153-166.
“The objectives of this study are to examine the landscape scale forest succession and the spatial and
temporal factors affecting natural restoration of human disturbed landscapes in eastern China.” (p. 155) this
study does not examine landscape change as a function of disturbance (either logging or fire or windthrow),
but simply tracks successional trajectories of the dominant tree species over a 300-year period (1990-2290).
“Simulation results suggest that an equilibrium in landscape structure and composition is approached on the
large landscapes dominated by shade tolerant species, but not on landtypes altered by humans. Equilibrium
can be observed in spruce-fir, mountain birch, and larch forests, but not in aspen-birch forests. Our results
suggest that direct nd indirect human impact may produce long-term alterations to forest landscape patch
structure that may persist for decades to centuries… e.g. even in a 300-year period of complete natural
succession, Korean pine only recovers on 1/3 of the landscapes it can dominate. …Landscape-scale
recovery appears to be limited by available seed sources…
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Yemshanov, D. and A. H. Perera. 2002. A spatially explicit stochastic model to simulate boreal forest cover
transitions: general structure and properties. Ecological Modeling 150(2002): 189-209.
V. Effects of Land Use (esp. forest harvest, also agriculture) on C-cycling:
General Overviews:
White, A and others. 2000. CO2 stabilization, climate change and the terrestrial carbon sink. Global
Change Biology. 6:817-833.
Houghton, R.A. and J. L. Hackler. 2000. Changes in terrestrial carbon storage in the United States.
I: The role of agriculture and forestry. Global Ecology and Biogeography. 9: 125-144.
Houghton, R.A. and J. L. Hackler. 2000. Changes in terrestrial carbon storage in the United States.
II: The role of fire and fire management. Global Ecology and Biogeography. 9: 145-170.
Houghton, R.A. and J. L. Hackler, and K. T. Lawrence. 1999. The U.S. Carbon budget:
Contributions from land use change. Science 285 (23 July 1999): 574-578.
Studies specific to Boreal forests
Kurz, W. A. and M. J. Apps (1994). “The carbon budget of Canadian forests: A sensitivity analysis
of changes in disturbance regimes, growth rates, and decomposition rates.” Environmental Pollution
83: 55-61.
This paper provides an earlier description of the CBM-CFS2 model. The only thing of note that I
found here was a statement saying that “…Canada’s commercially stocked forest area has been
declining (Honer et al. 1991), although reforestation efforts have greatly increased in recent years.” I
think the implication is that commercial harvesting is resulting in less regeneration of forest (or
slower regeneration) than would be expected following natural disturbance. This would be a
good point to follow up on.
Jiang, H. M. Apps, C. Peng, Y. Zhang, and J. Liu. 2002. Modelling the influence of harvesting on
Chinese boreal forest Carbon dynamics. Forest Ecology and Management 169 (2002): 65-82.
Lee, J. I. K. Morrison, J-D. Leblanc, M. T. Dumas and D. A. Cameron. Carbon sequestration in trees
and regrowth and partial cut harvesting in a second-growth boreal mixedwood. Forest Ecology and
Management 169 (2002): 83-101.
Rasmussen, L, C. Beier, and A. Bergstedt. 2002. Experimental manipulations of old pine forest
ecosystems to predict the potential tree growth effects of increased CO2 and temperature in a future
climate. Forest Ecology and Management 158 (2002): 179- 188.
VI. CO2 Change/ History
Liu, J., C. Peng, M. Apps, Q. Dang, E. Banfield, and W. Kurz. 2002. Historic Carbon budgets of
Ontario’s ecosystems. Forest Ecology and Management 169 (2002): 103-114.
Kurz, WA and Apps MJ. 1999. A 70-year retrospective analysis of carbon fluxes in the Canadian
forest sector. Ecological Applications 9(2):526-547.
OBJECTIVE: “The objective of this study was to analyze the change in ecosystem C storage in Canada’s
forest ecosystems over the 70-yr period 1920-1989. The analysis employs a detailed C accounting
framework that makes extensive use of national forest inventory information, long-term records of forest
disturbances, and simulation modeling.” p 526
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CBM-CFS2 models overmature forest biomass as decreasing exponentially from the peak mature
biomass level. However, “for uneven-aged stands (<1% of the area in the inventory) biomass is
assumed not to decline in the overmature growth phase” (p 529). So, my question: does the boreal
mixedwood significantly overlap with these uneven-aged stands? If so, does this imply that
converting the mixedwoods to monotypic stands for ease of forestry treatment has the overall
effect of reducing standing biomass? And what does this imply for ground layers and soil C?
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I strongly suspect that they are underestimating, or at least misestimating the belowground C
component; they are using allometric relationships between above- and belowground biomass that are
not robust. (p 531)
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Their model specifies 7 types of disturbances: wildfire, insect-induced stand mortality, clear-cut
logging, clear-cut logging with slash burning, salvage logging following wildfire, salvage logging
following insects-induced stand mortality, and partial cutting.
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In the model, harvesting is biased toward high-volume stands; insect disturbances are biased toward
mature and overmature softwood stands; fire occurs in all stands that have total biomass greater than or
equal to 1 Mg C/ha (p 531). It would be nice to find some empirical studies highlighting these factors.
(Nothing is cited here.)
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Figure 3: Nice graphs showing the importance of fire in the Boreal West (and Subarctic), and insects in
the Boreal East. Also shows how small (but steadily increasing) an area is affected by logging
compared to these disturbances.
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Important results: age-class structure has aged since 1920, with average Canadian forest stand age
increasing from 59.0 yr in 1920 to 81.5 by 1969, then decreasing to 78.2 by 1989. High disturbances
are posited for the late 19th and early 20th centuries, with a lull between 1920-1969, and then rates more
than doubling from 1970-1989. (p 537-8, and 541) They don’t mention it here, but I would guess to
put this in context, we should be aware that much of Canadian settlement history happened in the early
20th century, so we could reasonably expect those high late 19 th century disturbance rates to be mostly
“natural”, with perhaps some influence by native North Americans. I don’t know of any papers
covering past native land use in modern-day Canada, and I’m not sure we want to go there.
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Their model suggests that Canadian forests accumulated C in all years between 1920-1980, then began
losing C in the early 1980s (Figure 8). Integrated over this entire timespan, however, both total forest
biomass and total dead organic matter were still larger in 1990 than they were in 1920 (Fig 11 & 12).
The authors also refer to unpublished data of theirs showing that storage in the forest products pool
(including landfills) has also increased over this period (p 539). I don’t believe their analysis can
demonstrate whether land use has specifically led to changes in the pattern or amount of C storage.
We see clear changes in age-class structure over time, but harvest does not account for enough area to
dominate these trends. We do not learn anything about the role of anthropogenic fire or fire
suppression in contributing to these trends. I checked Web of Science for other papers that cite
Kurz & Apps’ work that may discuss causation for these trends, rather than just identifying the
trends. I don’t think I found any obvious answers, but I have a pile of papers to look through.
However it seems likely that the effects of natural disturbance have till now swamped
anthropogenic effects.
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Uncertainties: dead organic matter (DOM) C pool estimates (although they suggest the model is fairly
insensitive to this); accounting for salvage logging (again, they find the net ecosystem C flux #’s are
not very sensitive to this); statistical record of stand-replacing disturbance in 1920-1989 (the model is
sensitive to this, but I don’t follow the discussion) (p 543-4)
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Most land converted for agriculture in Canada was originally grassland, not forest, and so: “…the net
effects of land-use changes from forests to agriculture, and vice versa, are not considered to have
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significantly affected the forest sector C budget at the national scale, although regional effects could be
significant.”
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From Conclusions: “The CBM-CFS2 results suggest that forest ecosystems in Canada have been a
sink of atmospheric C for the period 1920-1980. In the decade of the 1980s, ecosystem C decreased as
a result of a >twofold increase in the area annually affected by stand-replacing disturbances, primarily
of natural origin…[results suggest that] the area annually disturbed in the period 1860-1920 was
greater than that in the 70 yr of this analysis…Note that this shift in age class structure [to older
forests] is not the result of regrowth from harvesting…
“The primary factor underlying the C sink to ~1970 was a change in the disturbance frequency
over a time scale of many decades, which resulted in changes in the average forest age and C content.
As the average forest age increases, the ability to sequester additional C decreases, and the
susceptibility to disturbances increases. It is therefore not likely that this forest sector C sink could
be sustained by maintaining a low disturbance rate through forest protection measures. Indeed,
the changes of the last two decades of the analysis period, whether due to human-induced climatic
change or natural variation, have resulted in significant changes in the disturbance regimes, relative to
the preceding half century. These disturbances have decreased the forest sector C sink and resulted in
a net decline in ecosystem C and in a release of C to the atmosphere.”

This may contribute to a table of values showing trends in global boreal forest C storage.
Kurz, W. A., M. J. Apps, et al. (1995). “20th century carbon budget of Canadian forests.” Tellus 47: 170177.
This paper mostly does not tell us anything that Kurz & Apps 99 doesn’t. But there are a couple
useful points to cite:
 “Forest fire suppression in Canada started on a very limited scale in the 1920s in response to widespread fires that had been reported throughout the country. In recognition of their ecological
importance and for economic considerations, fires are allowed to burn freely in Canada’s sparsely
populated northern regions (Stocks and Simard 1993). Fire suppression may have contributed to
reduced disturbances in the period 1920-1969, but wildfires in northern regions with limited
suppression increased greatly in the 1980s, which was the warmest decade in Canada’s 100-year
temperature record (Gullett and Skinner 1992). At present, it does not appear that direct human
activity has been the major reason for the observed changes in disturbance regimes of Canada’s
forests.” (p 175)
 Most lands converted for agriculture were previously grasslands, not forests. (p 175)
9
Useful papers I have but have not read yet (EAH):
Shvidenko, A. and S. Nilsson (2002). “Dynamics of Russian forests and the carbon budget in 19611998: An assessment based on long-term forest inventory data.” Climatic Change 55(1-2): 5-37.
ABSTRACT: Development trends of Russian forests and their impact on the global carbon
budget were assessed at the national level on the basis of long-term forest inventory data (1961-1998). Over
this period, vegetation of Russian forest lands are estimated as a carbon sink, with an annual average level
of carbon sequestration in vegetational organic matter of 210 +/- 30 Tg C . yr(-)1 (soil carbon is not
considered in this study), of which 153 Tg C . yr(-1) were accumulated in live biomass and 57 Tg C . yr(-1)
in dead wood. The temporal variability of the sink is very large; for the five-year averages used in the
analysis, the C sequestration varies from about 60 to above 300 Tg C . yr(-1). It is shown that long-term
forest inventory data could serve as an important information base for assessing crucial indicators of full
carbon accounting of forests.
This may complement Kurz & Apps 1999 for Russia, although it doesn’t cover soil C.
may contribute to a table of values showing trends in global boreal forest C storage.
This
Conard, S. G., A. I. Sukhinin, et al. (2002). “Determining effects of area burned and fire severity on
carbon cycling and emissions in Siberia.” Climatic Change 55(1-2): 197-211.
ABSTRACT: The Russian boreal forest contains about 25% of the global terrestrial biomass, and
even a higher percentage of the carbon stored in litter and soils. Fire burns large areas annually, much of it
in low-severity surface fires - but data on fire area and impacts or extent of varying fire severity are poor.
Changes in land use, cover, and disturbance patterns such as those predicted by global climate change
models, have the potential to greatly alter current fire regimes in boreal forests and to significantly impact
global carbon budgets. The extent and global importance of fires in the boreal zone have often been greatly
underestimated. For the 1998 fire season we estimate from remote sensing data that about 13.3 million ha
burned in Siberia. This is about 5 times higher than estimates from the Russian Aerial Forest Protection
Service (Avialesookhrana) for the same period. We estimate that fires in the Russian boreal forest in 1998
constituted some 14-20% of average annual global carbon emissions from forest fires. Average annual
emissions from boreal zone forests may be equivalent to 23-39% of regional fossil fuel emissions in
Canada and Russia, respectively. But the lack of accurate data and models introduces large potential errors
into these estimates. Improved monitoring and understanding of the landscape extent and severity of fires
and effects of fire on carbon storage, air chemistry, vegetation dynamics and structure, and forest health
and productivity are essential to provide inputs into global and regional models of carbon cycling and
atmospheric chemistry.
Banfield, G. E., J. S. Bhatti, et al. (2002). “Variability in regional scale estimates of carbon stocks in
boreal forest ecosystems: results from West-Central Alberta.” Forest Ecology and Management
169(1-2): 15-27.
ABSTRACT: Aboveground biomass, forest floor, and soil carbon (C) stocks were estimated for a
transitional boreal region in western Alberta using available forest inventory data, model simulation, field
observed plot data, and soil polygon (area averaged) information from the Canadian soil organic carbon
database (CSOCD). For the three C pools investigated, model simulation provided a regional estimate,
while forest inventory, plot, and soil polygon data provided an estimate of the spatial variation. These data
were used to examine the variation of the C estimates, in both temporal (e.g. climate change) and spatial
(e.g. soil physical characteristics) dimensions. Using the carbon budget model of the Canadian forest sector
(CBM-CFS2) the regional average aboveground biomass C was estimated at 43 Mg C ha(-2) similar to the
estimate from the 1994 Canadian forest inventory (50 Mg C ha(- 2)). Model simulation over the period
1920-1995 elucidated the major role that disturbances (harvest, fire and insects) play in determining the C
budget of the region. Decreases in stand replacing disturbances over the period resulted in an accumulation
in biomass C. Regional estimates of forest floor C using aggregated plot data, CSOCD (forested area only)
data, and CBM-CFS2 simulations were in close agreement, yielding values of 2.9, 3.4 and 3.3 kg C m(-2),
respectively. Regional estimates of total soil C using the three methods were more divergent (14.8, 8.3, and
15.6 kg C m(-2), respectively). An exponential relationship between clay content and biomass for
mature coniferous stand types was found (r(2) = 0.68), which is reasonable considering that as a site
10
variable, texture affects tree growth through the modification of nutrient and water availability. The
relationship was used to predict the range of potential values for biomass C at maturity across the region.
Forest inventories of biomass seldom provide enough data across the range of ages and stand types to
develop stand growth curves that capture the variation in growth across the landscape. Consequently,
growth dynamics must be inferred from a large area to provide enough biomass-to-age data, which results
in a loss in the ability to use it to predict C pools and fluxes at a small scale. Using relationships between
site factors (such as soil texture) and biomass C provides a means to modify inventory-based
biomass-to-age relationships to assess the variation across the region as well as make predictions at a
higher spatial resolution. This is relevant where both spatial extent and a finer scale are required,
but site-specific biomass-to-age relationships are unavailable.
This may provide some scaling rules, as well as being a good citation for the importance of soil
texture in influencing NPP.
Lee, J., I. K. Morrison, et al. (2002). “Carbon sequestration in trees and regrowth vegetation as
affected by clearcut and partial cut harvesting in a second- growth boreal mixedwood.” Forest
Ecology and Management 169(1-2): 83-101.
ABSTRACT: Ecosystem biomass and C sequestration and cycling were measured in a mature,
budworm-ravaged, second-growth boreal mixedwood stand subjected to clearcut and partial cut harvest
treatments. Ninety permanent sample plots, distributed among fifteen 10 ha blocks, were established in
1993 and remeasured shortly after harvest and, again, 5 years later to ascertain C removals, as well as postharvest ingrowth and upgrowth. In addition, litter bags and litter traps were installed and ground vegetation
and forest floor samples were collected to monitor changes in ecosystem C pools and fluxes as affected by
harvesting. The harvested blocks were quickly reoccupied by a thriving ground species regrowth, followed
by a prolific trembling aspen thicket. Despite this, 5-year growth per area on control plots exceeded that on
either partial cut or clearcut plots. Annual C assimilation rates in the post-harvest period were similarly
significantly higher on control (3.1 Mg ha(-1) per year) than on partial cut (1.8 Mg ha(-1) per year) or
clearcut (0.3 Mg ha(-1) per year) plots. When growth was expressed as a function of biomass, the order
reversed indicating the young growth to be the more vigorous. The forest floor lost little mass during the
post-harvest period. Further, leaf litter decomposition was slower on clearcut plots than in uncut forest.
Results suggest that ecosystem C pools and fluxes are rapidly reconstituted following harvest. If harvesting
were to occur, ecosystem C assimilation in boreal mixedwood forest would be maximized under partial
cutting.
Liu, J. X., C. H. Peng, et al. (2002). “Historic carbon budgets of Ontario's forest ecosystems.” Forest
Ecology and Management 169(1-2): 103-114.
ABSTRACT: Carbon (C) budgets of Ontario's forest ecosystems for the period 1920-1990 were
calculated using the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS2). Results show that
total forest biomass C in Ontario increased from 1.83 Pg (10(15) g) to 2.56 Pg between 1920 and 1970,
then decreased to 1.70 Pg by 1990. Carbon in soil and forest floor dead organic matter (DOM) increased
from 8.30 to 11.00 Pg between 1920 and 1985 but decreased to 10.95 Pg by 1990. Ontario's forest
ecosystems acted as a C sink sequestering 41-74 Tg (10(12) g) C per year from 1920 to 1975, but became a
C source releasing 7- 32 Tg C per year (5-year average) after 1975. Disturbances (fire, insects and
harvesting) enhanced both direct and indirect C emissions, and also affected average forest age and C
sequestration. Net primary production (NPP), net ecosystem production (NEP), and net biome production
(NBP) were affected by both disturbances and average forest age. Forests in the boreal (BO, 62.66 M ha),
cool temperate (CT, 7.77 M ha) and moderate temperate (MT, 0.20 M ha) regions had different C
dynamics. However, boreal forests dominated Ontario's forest C budget because of the large area and
associated C stock. Detailed C budgets for 1990 were also analyzed. The average forest ages in 1990 were
36.2 years for BO, 43.4 years for CT, and 92.1 years for MT regions, respectively. The total C stock of
Ontario's forest ecosystems (excluding peatlands) was estimated to be 12.65 Pg, including 1.70 Pg in living
biomass and 10.95 Pg in DOM and soil. Average C density was 179 Mg ha(- 1) (10(6) g) (24 Mg ha(-1) for
biomass and 155 Mg ha(-1) for DOM and soil). The total net C balance (excluding harvest removal) was 31.8 Tg. NPP, NEP and NBP were 267.6, -28.2 and - 40.6 Tg per year, respectively. The young age (36.2)
of Ontario's boreal forests indicates a great potential for C sequestration and storage. Roughly 1 Pg C could
be sequestered with a 10-year increase in forest age. A less severe disturbance regime and/or higher NPP
11
would convert Ontario's forest ecosystems back to a C sink.
Liski, J., D. Perruchoud, et al. (2002). “Increasing carbon stocks in the forest soils of western
Europe.” Forest Ecology and Management 169(1-2): 159-175.
ABSTRACT: The soils of western European forests may be accumulating carbon, because tree
biomass has been expanding in these forests already for decades, and the more numerous and larger trees
can produce more litter. We calculated the carbon budget of soils and trees in the forests of 14 EU countries
plus Norway and Switzerland from 1950 to 2040 by integrating forest resource information (inventory data
from 1950 to 1990 and a forest resource forecast from 2000 to 2040), biomass allocation and turnover
information, and a dynamic soil carbon model. The carbon stock of the soils increased throughout the
studied period. In 1990, the soil carbon sink was 26 Tg per year. This is 32 or 48% compared with our two
estimates of the tree carbon sink for that year. Until 2040, the soil carbon sink was estimated to increase to
43 Tg per year. This would already be 61 or 69% compared with the tree carbon sink that year. In 1990, the
soils contributed most to the total forest carbon sink in central Europe, where the soil carbon sink was
almost as large as the tree carbon sink. The soils were least important in southern Europe, where the soil
carbon sink was less than 25% compared with the tree carbon sink. In the future, the contribution of the
soils to the total forest carbon sink was estimated to increase everywhere except in southern Europe. The
soil carbon stocks increased mainly because litter fall from living trees increased while the other sources of
soil carbon, i.e. the residues of harvests and natural disturbances, varied less. This litter fall was also the
largest source of soil carbon accounting for 70-80% of the total. The soil carbon stocks in these forests
could thus be most effectively controlled by forest management actions, such as the choices of harvest
regimes or tree species, which especially affect the litter production of living trees. According to an
uncertainty analysis, we may have overestimated the soil carbon sink by 35% or underestimated it by 50%
throughout the studied period. The largest uncertainties were related to calculating the litter production of
living trees and decomposition in soil.
This may contribute to a table of values showing trends in global boreal forest C storage.
Bhatti, J. S., M. J. Apps, et al. (2002). “Influence of nutrients, disturbances and site conditions on
carbon stocks along a boreal forest transect in central Canada.” Plant and Soil 242(1): 1-14.
ABSTRACT: The interacting influence of disturbances and nutrient dynamics on aboveground
biomass, forest floor, and mineral soil C stocks was assessed as part of the Boreal Forest Transect Case
Study in central Canada. This transect covers a range of forested biomes-from transitional grasslands
(aspen parkland) in the south, through boreal forests, and into the forested subarctic woodland in the north.
The dominant forest vegetation species are aspen, jack pine and spruce. Disturbances influence biomass C
stocks in boreal forests by determining its age-class structure, altering nutrient dynamics, and changing the
total nutrient reserves of the stand. Nitrogen is generally the limiting nutrient in these systems, and N
availability determines biomass C stocks by affecting the forest dynamics (growth rates and site carrying
capacity) throughout the life cycle of a forest stand. At a given site, total and available soil N are
determined both by biotic factors (such as vegetation type and associated detritus pools) and abiotic factors
(such as N deposition, soil texture, and drainage). Increasing clay content, lower temperatures and reduced
aeration are expected to lead to reduced N mineralization and, ultimately, lower N availability and reduced
forest productivity. Forest floor and mineral soil C stocks vary with changing balances between complex
sets of organic carbon inputs and outputs. The changes in forest floor and mineral soil C pools at a given
site, however, are strongly related to the historical changes in biomass at that site. Changes in N availability
alter the processes regulating both inputs and outputs of carbon to soil stocks. N availability in turn is
shaped by past disturbance history, litter fall rate, site characteristics and climatic factors. Thus,
understanding the life-cycle dynamics of C and N as determined by age-class structure (disturbances) is
essential for quantifying past changes in forest level C stocks and for projecting their future change.
Goodale, C. L., M. J. Apps, et al. (2002). “Forest carbon sinks in the Northern Hemisphere.”
Ecological Applications 12(3): 891-899.
ABSTRACT: There is general agreement that terrestrial systems in the Northern Hemisphere
provide a significant sink for atmospheric CO2; however, estimates of the magnitude and distribution of
this sink vary greatly. National forest inventories provide strong, measuretment-based constraints on the
magnitude of net forest carbon uptake. We brought together forest sector C budgets for Canada, the United
12
States, Europe, Russia, and China that were derived from forest inventory information, allometric
relationships, and supplementary data sets and models. Together, these suggest that northern forests and
woodlands provided a total sink for 0.6-0.7 Pg of C per year (1 Pg = 10(15) g) during the early 1990s,
consisting of 0.21 Pg C/yr in living biomass, 0.08 Pg C/yr in forest products, 0.15 Pg C/yr in dead wood,
and 0.13 Pg C/yr in the forest floor and soil organic matter. Estimates of changes in soil C pools have
improved but remain the least certain terms of the budgets. Over 80% of the estimated sink occurred in
one-third of the forest area, in temperate regions affected by fire suppression, agricultural abandonment,
and plantation forestry. Growth in boreal regions was offset by fire and other disturbances that vary
considerably from year to year. Comparison with atmospheric inversions suggests significant land C sinks
may occur outside the forest sector.

This paper appears to summarize the inventory based data that we would be interested in, but
focuses on the 1990s (presumably because 1990 is the baseline for Kyoto accounting). Check it
for refs, stats, and discussion. The abstract, at least, glosses over the importance of long-term
trends in sequestration, which may present a very different picture than instantaneous snapshots
looking at only a couple recent decades.
Myneni, R. B., J. Dong, et al. (2001). “A large carbon sink in the woody biomass of Northern forests.”
Proceedings of the National Academy of Sciences of the United States of America 98(26): 1478414789.
ABSTRACT: The terrestrial carbon sink, as of yet unidentified, represents 15-30% of annual
global emissions of carbon from fossil fuels and industrial activities. Some of the missing carbon is
sequestered in vegetation biomass and, under the Kyoto Protocol of the United Nations Framework
Convention on Climate Change, industrialized nations can use certain forest biomass sinks to meet their
greenhouse gas emissions reduction commitments. Therefore, we analyzed 19 years of data from remotesensing spacecraft and forest inventories to identify the size and location of such sinks. The results, which
cover the years 1981-1999, reveal a picture of biomass carbon gains in Eurasian boreal and North
American temperate forests and losses in some Canadian boreal forests. For the 1.42 billion hectares of
Northern forests, roughly above the 30th parallel, we estimate the biomass sink to be 0.68 +/- 0.34 billion
tons carbon per year, of which nearly 70% is in Eurasia, in proportion to its forest area and in disproportion
to its biomass carbon pool. The relatively high spatial resolution of these estimates permits direct validation
with ground data and contributes to a monitoring program of forest biomass sinks under the Kyoto
protocol.
Amiro, B. D., B. J. Stocks, et al. (2001). “Fire, climate change, carbon and fuel management in the
Canadian boreal forest.” International Journal of Wildland Fire 10(3-4): 405-413.
ABSTRACT: Fire is the dominant stand-renewing disturbance through much of the Canadian
boreal forest, with large high-intensity crown fires being common. From 1 to 3 million ha have burned on
average during the past 80 years, with 6 years in the past two decades experiencing more than 4 million ha
burned. A large- fire database that maps forest fires greater than 200 ha in area in Canada is being
developed to catalogue historical fires. However, analyses using a regional climate model suggest that a
changing climate caused by increasing greenhouse gases may alter fire weather, contributing to an
increased area burned in the future. Direct carbon emissions from fire (combustion) are estimated to
average 27 Tg carbon year(-1) for 1959-1999 in Canada. Post-fire decomposition may be of a similar
magnitude, and the regenerating forest has a different carbon sink strength. Measurements indicate that
there is a net carbon release (source) by the forest immediately after the fire before vegetation is reestablished. Daytime downward carbon fluxes over a burned forest take 1-3 decades to recover to those of a
mature forest, but the annual carbon balance has not yet been measured. There is a potential positive
feedback to global climate change, with anthropogenic greenhouse gases stimulating fire activity through
weather changes, with fire releasing more carbon while the regenerating forest is a smaller carbon sink.
However, changes in fuel type need to be considered in this scenario since fire spreads more slowly
through younger deciduous forests. Proactive fuel management is evaluated as a potential
mechanism to reduce area burned. However, it is difficult to envisage that such treatments could be
employed successfully at the national scale, at least over the next few decades, because of the large
scale of treatments required and ecological issues related to forest fragmentation and biodiversity.
13
Schimel, D. S., J. I. House, et al. (2001). “Recent patterns and mechanisms of carbon exchange by
terrestrial ecosystems.” Nature 414(6860): 169-172.
ABSTRACT: Knowledge of carbon exchange between the atmosphere, land and the oceans is
important, given that the terrestrial and marine environments are currently absorbing about half of the
carbon dioxide that is emitted by fossil-fuel combustion. This carbon uptake is therefore limiting the extent
of atmospheric and climatic change, but its long-term nature remains uncertain. Here we provide an
overview of the current state of knowledge of global and regional patterns of carbon exchange by terrestrial
ecosystems. Atmospheric carbon dioxide and oxygen data confirm that the terrestrial biosphere was
largely neutral with respect to net carbon exchange during the 1980s, but became a net carbon sink
in the 1990s. This recent sink can be largely attributed to northern extratropical areas, and is roughly split
between North America and Eurasia. Tropical land areas, however, were approximately in balance with
respect to carbon exchange, implying a carbon sink that offset emissions due to tropical deforestation. The
evolution of the terrestrial carbon sink is largely the result of changes in land use over time, such as
regrowth on abandoned agricultural land and fire prevention, in addition to responses to
environmental changes, such as longer growing seasons, and fertilization by carbon dioxide and
nitrogen. Nevertheless, there remain considerable uncertainties as to the magnitude of the sink in different
regions and the contribution of different processes.
Malmstrom, C. M. and K. F. Raffa (2000). “Biotic disturbance agents in the boreal forest:
considerations for vegetation change models.” Global Change Biology 6: 35-48.
ABSTRACT: Disturbance regimes strongly determine vegetation patterns and succession in the
boreal landscape. One of the current challenges for boreal vegetation modellers is to represent disturbance
agents as dynamic factors that can respond to climate change. Outbreak species of insects and plant
pathogens can cause marked changes in vegetation patterns and should be incorporated into vegetation
change models. This introduction to the ecology of boreal biotic disturbance agents is designed as a brief
overview for global change researchers and modellers. We discuss the importance of biotic disturbance
agents in the boreal forest, offer an overview of their ecology, and review modelling approaches. We
illustrate these issues with examples from different systems, drawing largely from our experience with bark
beetles.

Good for background on insects?
Volney, W. J. A. and R. A. Fleming (2000). “Climate change and impacts of boreal forest insects.”
Agriculture Ecosystems & Environment 82(1-3): 283-294.
ABSTRACT: The circum-polar boreal forest has played an important role in the wealth of
northern nations since the 15th century. Its natural resources spurred strategic geopolitical developments
beginning in the 16th century but intense development of the boreal forest is largely limited to the 20th
century. Insects cause considerable loss of wood that has an adverse effect on the balance of carbon
sequestered by forests. Current understanding of processes that lead to stand-replacing outbreaks in three
insect species is reviewed in this paper. Many of these processes depend on climate either directly, such as
reduced survival with extreme weather events, or indirectly, mainly through effects on the host trees. In the
boreal zone of Canada, pest-caused timber losses may be as much as 1.3-2.0 times the mean annual
depletions due to fires. Pests are thus major, but consistently overlooked forest ecosystem components that
have manifold consequences to the structure and functions of future forests. Global change will have
demonstrable changes in the frequency and intensity of pest outbreaks, particularly at the margins of host
ranges. The consequent shunting of carbon back to the atmosphere rather than to sequestration in forests as
biomass is thought to have positive feedback to global warming. Whereas significant progress has been
made in developing carbon budget models for the boreal forests of Canada, enormous problems remain in
incorporating pest effects in these models. These problems have their origins in the nature of interactions
among pests with forest productivity, and problems with scaling. The common problems of verification and
validation of model results are particularly troublesome in projecting future forest productivity. The
interaction of insects with fires must be accounted for if realistic carbon sequestration forecasts in a
warming climate are to be made, These problems make assessments of mitigation and adaptation of pest
management alternatives difficult to evaluate at present. Nevertheless, the impacts of stand-replacing insect
population outbreaks is important in formulating future resource management policy.
14

Good for background on insects?
Chen, W. J., J. Chen, et al. (2000). “An integrated terrestrial ecosystem carbon-budget model based
on changes in disturbance, climate, and atmospheric chemistry.” Ecological Modelling 135(1): 55-79.
ABSTRACT: Disturbances (e.g. fire, insect-induced mortality, and harvest) and management
practices (e.g, planting) affect the forest carbon (C) cycle, so do non-disturbance climatic and atmospheric
factors (e.g. growing season length and temperature, abiotic decomposition factor, annual precipitation,
atmospheric CO2 concentration, and nitrogen (N) deposition). Previous studies investigated the effects of
these factors individually or in some combinations, but not their integrated effects at regional and global
scales. This study describes an Integrated Terrestrial Ecosystem C-budget model (InTEC), which integrates
effects of all these factors on the annual C cycle of a forest region. InTEC is based on the Farquhar's leaf
photosynthesis model, the Century C cycle model, the net N mineralization model of Townsend et al.
[Ecol. Appl., 6 (1996) 806] and an age-NPP relationship derived from forestry inventory-based agebiomass relationships. To integrate these existing models, which were developed for different purposes and
had different spatial and temporal scales, into a coherent mechanistic model, we (1) develop a spatial and
temporal up-scaling algorithm to use the instantaneous leaf-level model for a region at annual time step;
and then (2) combine the upscaled results with an age-NPP relationship to obtain the annual NPP of a forest
region. A historical change approach is then used to describe the regional annual C cycle, which not only
improves the accuracy of its historical and present estimates, but also enables us to predict its future
responses, both of which are critical in formulating mitigation and adaptation strategies for global changes.
Applying InTEC to Canada's forests, we first investigate the impacts of each factor on the C cycle over the
short term (i.e. in the year of perturbation) and the long term (i.e. in the years after perturbation). The shortterm and long-term effects are determined by changing one of the 10 factors in year 1 since the
industrialization while keeping this factor in all other years and all other factors in all years at pre-industrial
levels. Integrating all these short- term and long-term effects for the actual historical data of the 10 external
forcing factors, we then estimate that the annual mean NBP (= NPP - soil respiration - fire emission - forest
praoducts oxidation) of Canada's forests was 40 +/- 20 Tg C per year (i.e. a sink) in 1810s, reduced to - 131
+/- 66 Tg C per year (i.e. a source) in 1870s, increased thereafter to a maximum of 200 +/- 100 Tg C per
year in 1930s, and decreased again to 57 +/- 27 Tg C per year in 1990s. From 1800 to 1998, the
aboveground biomass of Canada's forests increased by similar to 19%, while the soil C stock increased by
similar to 2%. (C) 2000 Elsevier Science B.V. All rights reserved.
Houghton, R. A. and J. L. Hackler (2000). “Changes in terrestrial carbon storage in the United
States. 1: The roles of agriculture and forestry.” Global Ecology and Biogeography 9(2): 125-144.
ABSTRACT: 1 Changes in the areas of croplands and pastures, and rates of wood harvest in
seven regions of the United States, including Alaska, were derived from historical statistics for the period
1700-1990. These rates of land-use change were used in a cohort model, together with equations defining
the changes in live vegetation, slash, wood products and soil that follow a change in land use, to calculate
the annual flux of carbon to the atmosphere from changes in land use. 2 The calculated flux increased from
less than 10 TgC/yr in 1700 to a maximum of about 400 TgC/yr around 1880 and then decreased to
approximately zero by 1950. The total flux for the 290-year period was a release of 32.6 PgC. The area of
forests and woodlands declined by 42% (160 x 10(6) ha), releasing 29 PgC, or 90% of the total flux.
Cultivation of soils accounted for about 25% of the carbon loss. Between 1950 and 1990 the annual flux of
carbon was approximately zero, although eastern forests were accumulating carbon. 3 When the effects of
fire and fire exclusion (reported in a companion paper) were added to this analysis of land-use
change, the uptake of carbon calculated for forests was similar in magnitude to the uptake measured
in forest inventories, suggesting that past harvests account for a significant fraction of the observed
carbon sink in forests. 4 Changes in the management of croplands between 1965 and 1990 may have led
to an additional accumulation of carbon, not included in the 32.6 PgC release, but even with this additional
non-forest sink, the calculated accumulation of carbon in the United States was an order of magnitude
smaller than the North American carbon sink inferred recently from atmospheric data and models.
Houghton, R. A., J. L. Hackler, et al. (1999). “The US carbon budget: Contributions from land-use
change.” Science 285(5427): 574-578.
ABSTRACT: The rates at which lands in the United States were cleared for agriculture,
abandoned, harvested for wood, and burned were reconstructed from historical data for the period 1700-
15
1990 and used in a terrestrial carbon model to calculate annual changes in the amount of carbon stored in
terrestrial ecosystems, including wood products. Changes in land use released 27 +/- 6 petagrams of carbon
to the atmosphere before 1945 and accumulated 2 +/- 2 petagrams of carbon after 1945, Largely as a result
of fire suppression and forest growth on abandoned farmlands. During the 1980s, the net flux of carbon
attributable to land management offset 10 to 30 percent of U.S. fossil fuel emissions.
Papers to get:
Yu, Z. C., M. J. Apps, et al. (2002). “Implications of floristic and environmental variation for carbon
cycle dynamics in boreal forest ecosystems of central Canada.” Journal of Vegetation Science 13(3):
327-340. (Not available online)
ABSTRACT: Species composition, detritus, and soil data from 97 boreal forest stands along a
transect in central Canada were analysed using Correspondence Analysis to determine the dominant
environmental/site variables that differentiate these forest stands. Picea mariana stands were densely
clustered together on the understorey DCA plot, suggesting a consistent understorey species composition
(feather mosses and Ericaceae). whereas Populus tremuloides stands had the most diverse understorey
species composition (ca. 30 species, mostly shrubs and herbs). Pinus banksiana stands had several
characteristic species of reindeer lichens (Cladina spp.), but saplings and Pinus seedlings were rare.
Although climatic variables showed large variation along the transect, the CCA results indicated that site
conditions are more important in determining species composition and differentiating the stand types.
Forest floor characteristics (litter and humus layer, woody debris, and drainage) appear to be among the
most important site variables. Stands of Picea had significantly higher average carbon (C) densities in the
combined litter and humus layer (43530 kg- C.ha(-1)) than either Populus (25500 ka-C.ha(-1)) or Pinus
(19400 kg-C.ha(-1)). The thick surface organic layer in lowland Picea stands plays an important role in
regulating soil temperature and moisture, and organic-matter decomposition, which in turn affect the
ecosystem C-dynamics. During forest succession after a stand-replacing disturbance (e.g. fires), tree
biomass and surface organic layer thickness increase in all stand types as forests recover; however, woody
biomass detritus first decreases and then increases after ca. 80 yr. Soil C densities show slight decrease with
ages in Populus stands, but increase in other stand types. These results indicate the complex C-transfer
processes among different components (tree biomass, detritus, forest floor, and soil) of boreal ecosystems
at various stages of succession.
This may provide scaling rules, or ideas of how species and pattern interact?
16