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Forest Research Information Paper
No.
143
The Impacts of Climate Change
on Ontario's Forests
Ministry of
Natural
Resources
Forest Research Information Paper
No.
143
The Impacts of Climate Change
on Ontario's Forests
by
S.J. Colombo*, M.L. Cherry, C. Graham
S. Greifenhagen, R.S. McAlpine, C.S. Papadopol
W.C. Parker, T. Scarr, M.T. Ter-Mikaelian
Ontario Ministry of Natural Resources
and
M.D. Flannigan
Canadian Forest Service
S.J. Colombo and L.J. Buse
Editors
1998
Ontario Forest Research Institute (OFRI)
Ontario Ministry of Natural Resources
1235 Queen St. E., Sault Ste. Marie, ON
P6A 2E5 Canada
Tel. (705) 946-2981, Fax. (705) 946-2030
*E-mail: [email protected]
Canadian Cataloguing in Publication Data
Main entry under title:
The impacts of climate change on Ontario's forests
S.J. Colombo ...[et al.]
(Forest research information paper, ISSN 1319-9118 ; no. 143)
Includes bibliographical references.
ISBN 0-7778-7588-8
1. Climatic changes—Ontario. 2. Forests and forestry—Ontario.
Forest microclimatology—Ontario. I. Colombo, S.J. (Stephen John).
II. Ontario Forest Research Institute. III. Series.
SD390.7C55146 1998
577.3'722'90713
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C98-964023-X
3.
Abstract
This report reviews literature concerning the effects of global climate change on forest plants
and communities and provides author’s opinions of the potential impacts climate change may have
on Ontario’s forests. There is growing evidence that environmental changes caused by elevated
atmospheric carbon dioxide (CO2) and its potential effects on global climate will alter forest ecosystems in Ontario. A doubling of CO2 from pre-industrial levels is expected to occur within 80 years.
Increased CO2 may increase average summer temperatures in Ontario between 3°C and 6°C, with the
largest increases in northwestern and southern Ontario. Precipitation is predicted to increase in
northeastern Ontario, but to decrease in southern and northwestern Ontario. An increase in summer
temperatures with no or little increase in precipitation would increase the frequency and severity of
drought by elevating evapotranspiration. In addition, the incidence of extreme weather events and
variation in weather are expected to increase.
The length of the forest fire season is expected to increase with longer growing seasons. In
addition, increased moisture loss from forests due to elevated temperatures would increase forest fire
frequency and severity. Forest plant diseases and insects attack plants that have been stressed: increases in drought could also increase the frequency of major insect and disease outbreaks. An
increase in forest fires, insect outbreaks and diseases would, in turn, alter the age structure and plant
species in forest ecosystems, with the greatest impacts expected in northwestern and southern Ontario. Extreme weather events, such as ice storms, floods, and very high or widely fluctuating temperatures could further damage or stress plants.
Increased CO2, drought, and temperature will affect the growth and survival of plants by
altering their physiological behaviour. The genetic structure of plant populations may be affected by
altered selection pressures resulting from a changed environment, and species with larger genetic
variability are likely more adaptable to a variety of climate conditions and as a result may be more
successful. Competitive abilities of plant species now present in Ontario’s forests may change, with
some species becoming more competitive and others less so (e.g., herbaceous plants are favoured by
increased CO2 compared to woody plants). Productivity and timber supply in northwestern and
southern Ontario may decline due to increases in drought, forest fires, insects and disease. However,
this could be partially offset by increases in growth rates accompanying higher CO2 levels, warmer
temperatures, and a longer growing season. Increases in precipitation in northeastern Ontario along
with higher CO2 levels, increased temperatures and longer growing season could significantly increase productivity and timber supply in that region. Over hundreds of years, plant species may
migrate northward. In one scenario, tolerant hardwood forests of central Ontario may migrate as far
north as Kapuskasing. Species, such as those of the oak-hickory forests of the central U.S., may
eventually migrate into what is currently the Great Lakes-St. Lawrence forest. However, differing
migration rates and the reactions of individual species to new environmental conditions could result
in new plant species mixes for which we lack forest management experience.
Forest management offers some means of reducing negative impacts to forests if the anticipated
levels of climate change occur. Thinning to reduce moisture stress and early harvesting of stands
deteriorating due to stress, followed by planting with more climatically adapted populations and
species could help maintain higher levels of productivity. Climatic adaptation could be increased
through tree breeding aimed at increasing pest and stress tolerance. Forests are important for their
role in absorbing and storing carbon from the atmosphere. Although not presently a stated goal,
carbon sequestration (storage) could in the future become an objective of forest management. Carbon
sequestration is maximized by silvicultural practices that increase tree growth rates but release little
carbon through the burning of fossil fuels. Process-based models of specific elements of forest ecosystems will be needed to predict the effects of climate change and consequently to develop forest
management practices that will minimize negative effects on Ontario’s forests.
Acknowledgements
We are grateful to the following individuals for providing technical reviews of individual
sections of this report:
2. Climate
Mike Wotton, Canadian Forest Service (CFS)
3. Hydrology
Michael Ter-Mikaelian, OFRI, Ontario Ministry of Natural Resources
(OMNR)
5. Fungi
Mike Dumas, CFS
Tim Meyer, OFRI, OMNR
6. Forest Fires
Mike Wotton, CFS
Al Tithecott, Aviation, Flood and Fire Management Section,
OMNR
7. Physiology
Francine Bigras, CFS
8. Genetics
Cheng C. Ying, B.C. Ministry of Forests
9. Succession
Wayne Bell, OFRI, OMNR
10. Modelling
Art Groot, CFS
Rich Fleming, CFS
11. Silviculture
Luc Duchesne, CFS
Our appreciation is also extended to Lisa Buse for editing the document for style, Trudy
Vaittinen for desktop publishing and graphics, and Anne Rovansek for typing.
Contents
Section 1.
Section 2.
Section 3.
Section 4.
Section 5.
Section 6.
Section 7.
Section 8.
Section 9.
Section 10.
Section 11.
Section 12.
Introduction ................................................................................................................................................ 7
Stephen J. Colombo, Celia Graham, Michael T. Ter-Mikaelian
Ontario's Climate in the 21st Century ....................................................................................................... 9
Mike D. Flannigan
Forest Hydrology in Relation to Global Change ................................................................................... 12
Chris S. Papadopol
Insects and Climate Change ................................................................................................................... 16
Taylor Scarr
The Impact of Climate Change on Fungi in the Forest Ecosystem ................................................... 18
Sylvia Greifenhagen
The Impact of Climate Change on Forest Fires and Forest Fire Management .................................. 21
Robert S. McAlpine
Plant Physiological Responses to a Changing Environment............................................................. 25
Stephen J. Colombo
Genetic Implications of Climate Change ............................................................................................... 29
Marilyn L. Cherry
Climate Change and Forest Vegetation Dynamics in Ontario ............................................................. 33
William C. Parker
The Use of Models in Global Climate Change Studies ......................................................................... 36
Michael T. Ter-Mikaelian
Forest Management Responses to Climate Change ............................................................................ 40
William C. Parker, Stephen J. Colombo, Marilyn L. Cherry, Sylvia Greifenhagen, Chris S. Papadopol, Taylor Scarr
Conclusions ............................................................................................................................................. 50
References ................................................................................................................................................ 51
Section 1.
Introduction
Stephen J. Colombo, Celia Graham, and
Michael T. Ter-Mikaelian, Ministry of Natural
Resources
The accumulation of carbon dioxide
(CO2) in the atmosphere and the changes
this may cause to climate have potentially
important consequences for Ontario’s
forested ecosystems. While forests tend to
be viewed as unchanging due to the long
life spans of trees compared to humans,
forests in Ontario have been changing as a
result of human activity since the middle
of the 19th century (Armson et al. 1998).
Historically, harvesting has been the major
contributor to changes in species composition and distribution of forest types. However, since about the middle of the 20th
century, forests in Ontario and elsewhere
in North America have also been affected
by other aspects of human activity: the
acidification of forest soils and the deposition of nitrogen as a by-product of industrial pollution have altered soil chemistry
throughout much of central and southern
Ontario; ground-level ozone pollution,
primarily in southern and central Ontario,
has direct damaging effects on forest
vegetation; the reduction of ozone high in
the earth’s atmosphere has increased
ultraviolet radiation reaching the earth,
with potentially serious effects on some
plant species. Each of these factors by
themselves is a contributor to changes in
Ontario’s forests. Climate change, resulting
from increased atmospheric CO2, is expected to interact with the above factors to
significantly alter the composition and
function of forest ecosystems in Ontario
(Schindler 1998).
There is growing concern that the
increase in atmospheric CO2 (and other
gases produced by human activity, such as
methane and chlorofluorocarbons) will
increase air temperatures as a result of the
“greenhouse effect” (Kuo et al. 1990). The
trapping of heat by greenhouse gases that
occurs naturally is beneficial as it maintains warm temperatures over most of the
globe at suitable levels for agriculture and
forests. However, industrial pollution will
result in an approximate doubling of
atmospheric CO2 by the end of the next
century. Examination of very long time
scale polar ice cores shows a strong correlation between temperature and the concentration of CO2 in the atmosphere. Accumulating greenhouse gases such as CO2
will trap an increasingly larger portion of
the re-radiating solar energy in the atmosphere, and this may warm the earth measurably above current levels (Kräuchi 1994).
According to Kräuchi (1994), the warming
seen over the last century is almost certainly (i.e., with greater than 99% probability) the result of a real warming trend, and
this warming is associated with an increase in atmospheric CO2. Precipitation
patterns are also likely to be altered in the
event of climate warming, with some areas
becoming wetter and others drier (Joyce et
al. 1990). The frequency of extreme
weather events is also expected to increase
(Hengeveld 1995), with potential increases
in the occurrence of severe drought, very
high temperatures, ice storms, and rapidly
fluctuating temperatures.
Forest management practices must
change to keep pace with climatically
induced changes in forest ecosystems.
Models are required to predict these
changes, since forests are complex ecosystems that often respond to climate in
unexpected ways both structurally (i.e., the
species and ages of plants and animals in
the ecosystem) and functionally (i.e.,
physiological and biogeochemical processes). Even our understanding of the
effects of the present climate on forest
ecosystems is incomplete and climate
change effects cannot be predicted solely
by interpolation from present day field
conditions or from laboratory experiments.
In the future, forest ecosystems will be
affected by climate change in ways that
have never been observed or for which
data are unavailable, and predictions
based on present forest conditions may not
be relevant. Models are also useful because
forest ecosystems are hierarchical (i.e.,
effects controlling ecosystem structure and
function can occur at scales ranging from
regional to as small as an individual plant
and soil microbial populations), and have
many components that may be affected
differently both in terms of the magnitude
and direction of change. Even if one knew
the separate effects of climate change on
each component, their interactions would
prevent assembling these effects into an
adequate description of complex ecosystem effects. Thus, models are the best tool
we have to predict the effects of climate
change on forest ecosystems.
Increasing recognition of climate
change has lead to an international agreement to reduce greenhouse gas emissions
through the United Nations Framework
Convention for Climate Change in 1992 and
the Kyoto Protocol in December 1997. The
role of forests in sequestering and storing
carbon is established in this Convention
and Protocol. Countries that ratify the
Protocol will report on the area of managed forests, reforestation (renewal of
harvested forests), afforestation (conversion of non-forested to forested land) and
deforestation (loss of forest). Forests established between 1990 and 2012 may be
counted as contributions towards Canada’s emission reduction target of 6%, as
defined by the Kyoto Protocol.
Ontario needs to begin to formulate
the role of forest ecosystems and forestry
as part of a broader response to the international commitment to address climate
change. The sustainability, biodiversity,
health, and economic benefits of forests
may be affected to varying degrees by
climate change. The long-lived nature of
trees requires that we consider the effects
of practices for periods of at least one
rotation but preferably for several rotations (e.g., 200-300 years). It is the responsibility of the Ontario Ministry of Natural
Resources (OMNR) as the steward of
Crown forests to understand the potential
effects of climate change on forests and
begin to incorporate these effects into its
planning. The OMNR’s mandate to sustain
the health and integrity of natural resources will need to include policies and
guidelines to manage for mitigation and
adaptation to climate change. One of the
first steps is to develop an understanding
of the impacts of climate change on Ontario’s natural resources.
This discussion paper examines the
multiple effects of climate change on
Ontario’s forest ecosystems. The co-authors of this report have prepared sections
addressing the key issues and impacts in
their respective disciplines. Some possible
actions to mitigate adverse effects of climate change are addressed in the section
“Forest Management Responses to Climate
Change.“
Section 2.
Ontario's Climate in the 21st Century
Mike D. Flannigan, Canadian Forest
Service
While we tend to think of climate as
being constant, in fact it is always changing. Some changes follow patterns with
extremely long time scales, such as the
21,000 year cycle of the precession of the
earth’s axis about the pole. Weather, in
comparison, is by definition variable, and
is the short-term (hours to months) variation of the atmosphere. Climate is the
weather at some location averaged over a
specified time period (typically 30 years)
plus information on the variability and
weather extremes. Climate, and its associated weather, influence the natural environment directly, through elements such
as temperature and precipitation, and
indirectly, through its influence on disturbance and permafrost. Any change in
variability in climate could be critical
because many of the ecological impacts of
climate are the result of extremes. At the
local scale, climate is influenced by variations in solar radiation due to latitude,
distribution of continents and oceans,
atmospheric pressure and wind systems,
ocean currents, major terrain features,
proximity to water bodies, and local features, such as exposure, local topography,
and urbanization (see Trewartha and Horn
1980).
The “greenhouse effect” is the influence of gases such as carbon dioxide,
water vapour and methane on the earth’s
radiation budget. The greenhouse gases in
our atmosphere allow the shorter wavelength radiation (incoming solar) to reach
the earth’s surface while absorbing the
longer wavelengths (outgoing terrestrial),
which, in part, is re-radiated back to the
earth. Human activities have increased
carbon dioxide, methane and other natural
greenhouse gases, in the atmosphere, as
well as added human-made gases such as
chlorofluorocarbons (CFCs) and
hydroflurocarbons (HFCs). Increases in
greenhouse gas concentrations are responsible for enhancing the natural greenhouse
effect. Global mean surface air temperature has increased by 0.3° to 0.6°C since
the late 19th century (Intergovernmental
Panel on Climate Change (IPCC) 1996).
For Ontario, surface air temperatures have
risen by 0.5° to 0.7°C since 1895 (Gullett
and Skinner 1992). The IPCC (1996) states
that “the balance of evidence suggests a
discernible human influence on global
climate” and that the climate is expected to
continue to change in the future. Incontrovertible attribution of the long-term cause
of current climate change is difficult due to
the natural short-term variability in the
earth’s climate. Future predictions are
difficult because of the complex interactions in the climate system.
General Circulation Models (GCMs),
sophisticated computer models, are the
primary tool used to estimate what the
future climate will be. Numerous GCMs
are used (Lau et al. 1996), including a
Canadian GCM (Boer et al. 1992,
McFarlane et al. 1992). Most GCMs have
outputs for 1xCO2 and 2xCO2 scenarios,
which roughly correspond to atmospheric
CO2 conditions in the mid-20th century
and the second half of the 21st century,
respectively. GCMs suggest that the average global surface air temperature will
increase by 1 to 3.5°C by 2100 (IPCC 1996).
However, more pronounced changes
should occur at high latitudes and be
greatest in winter. The spatial resolution of
these models is often around 400 km.
Regional Climate Models are now being
developed to provide climate
estimates at finer spatial resolution (~40
km). These will be more suitable for predicting regional effects of climate change in
Ontario (Caya et al. 1995).
The present climate of Ontario is best
described as continental, with cold winters
and warm to cool summers. The climate
around the Great Lakes tends to be
warmer and wetter in winter because of
the heat and moisture available from the
large bodies of water. Conditions range
from warm and moist in the south to cold
and dry in the northwest (Table 2.1). A
more detailed discussion of the recent
climate of Ontario can be found in Hare
and Thomas (1974).
Projected global warming of 1 to 3.5°C
over the next century means that the climate would warm at a rate faster than at
any time in the past. These increased
temperatures could make the next century
the warmest so far during this interglacial
period. Ontario is a large and diverse
geographical region with great variation in
climate. Figure 2.1 shows the predicted
increase in surface air temperature during
the 1 May - 31 August period derived from
the Canadian GCM, comparing a doubled
(i.e., 2xCO2) to present (i.e., 1xCO2) CO2
concentration. According to this scenerio,
temperature increases of 3°C to over 5°C
are expected across Ontario. The largest
increases are expected over southwestern
sections of northwestern Ontario, while the
smallest increases are anticipated over the
extreme northwestern region of Ontario
along Hudson’s Bay. If these predictions
are realized, the summer temperature
regime in Sudbury at the end of the next
century would be similar to the current
summer temperature regime in Windsor
(Table 2.1).
Figure 2.2 shows the predicted effect
of a doubled CO2 environment on summer
precipitation across Ontario, according to
the Canadian GCM. Values over 1.0 indicate increases in precipitation whereas
values less than 1.0 indicate decreases in
precipitation for the end of the next century. Precipitation ratios range from just
under 1.0 for much of northwestern Ontario and most of southern Ontario to over
1.2 for northeastern Ontario. There is
increased potential for water stress over
regions with decreased precipitation in
conjunction with increased temperatures.
Precipitation has been increasing since
1910 over the continental United States and
most of this increase is due to increased
frequency of extremely heavy precipitation
events (Karl and Knight 1998). An increase
in the number and severity of extreme
weather events also is predicted to result
from climate change.
The impacts of climate change have
broad and far reaching implications for
Ontario’s forests, ranging from disturbances (insects, disease, fire and wind) and
biotic responses (physiology, genetics and
plant succession) to how we manage our
forests within this new environment (Weber
and Flannigan 1997). The continued development of regional circulation models with
shorter time intervals will be important to
predict and respond to the impacts of climate change on Ontario’s forests.
Table 2.1. Selected climate data for selected sites across Ontario from 1961-90 (Environment Canada 1993).
Station
Latitude
(0N)
Longitude
(0W)
Mean
annual temp.
(0C)
Mean
annual prec.
(mm)
Mean
January temp.
(0C)
Mean
July temp.
(0C)
Growing
degree days
(base 50C)
Windsor
42
83
9.1
902
-5.0
22.4
2544
Sudbury
47
81
3.5
872
-13.5
19.1
1680
Big Trout Lake
54
90
-2.8
598
-23.9
16.2
1075
Section 3.
Forest Hydrology in Relation to Global Change
Chris Papadopol, Ontario Forest Research
Institute, Ministry of Natural Resources
Water availability to forest plants
varies with precipitation, evaporative
demand and the capacity of the soil to store
water. Climate warming may modify water
availability by changing precipitation and
evaporative demand. The soil water balance of forested sites is important because
water availability strongly affects forest
productivity; numerous studies show that
drier than normal seasons reduce tree ring
size.
Forest ecosystems can also modify the
local hydrology and environment. Forests
affect the environment locally and seasonally through albedo (i.e., reflectivity of
sunlight), roughness (i.e., evenness of the
canopy) and transpiration. Under favourable conditions, forests also have the potential to mitigate some of the local effects of
climate change expected in the next century, for example by acting as CO2 sinks
(i.e., enhancing biomass and litter production) (see Section 11).
Climate warming will accelerate the
circulation of moisture in the global water
cycle (Bolin 1986). Since regional precipitation depends on major air circulation patterns, climate change may either increase or
decrease the amount of precipitation in a
given area (see Section 2, Figure 2.2). Anticipated increases in summer temperatures
will increase evapotranspiration from
forests. The increased Atmospheric Demand for Evaporation, ADE, is an important way that climate warming may influence vegetation. Where soil water storage is
poor (e.g., coarse textured and thin soils),
an increase in ADE may reduce soil water
availability, and through this, gradually
change the productivity and survival of
forest plants.
Models of forest water balance can
provide estimates of soil water availability
on sites where soil texture and forest plant
species are known. It may be possible to use
such models to develop regional estimates
of forest water use where the spatial distribution of soil texture and plant species are
known. To show the influence of warming
on ADE, the Thornthwaite model for
evapotranspiration, ETp (Thornthwaite
1946), was run for three scenarios: (i) no
thermal increase, recorded mean air temperature (ETpO), (ii) recorded mean air
temperature + 2oC (Etp2), and (iii) recorded
mean air temperature + 4oC (Etp4), using
historic daily data from Blind River, Ontario, and soil hydraulic conductivity for a
typical stand in the Kirkwood forest, near
Thessalon, Ontario. A water balance model
was then run to simulate water availability
in past growing seasons.
Warming increases evapotranspiration
with every degree Celsius in temperature
causing an additional 0.15 mm/day or 4.5
mm/month ADE (Figure 3.1). This increase
should be interpreted in the context of the
range of daily ADE, which during the
growing season in Ontario, roughly varies
between 6 and 2 mm/day from south to
north. This increase in evapotranspiration
will reduce soil moisture and, in my opinion, may limit the distribution of some
species and reduce the productivity of
others. In comparison with recent historical
conditions, the future soil water regime of
some regionsof Ontario will be less favourable, especially on soils with high hydraulic conductivity, which cover large areas of
Ontario.
An example of the possible site effects
of increased evapotranspiration is given in
Figure 3.2, for a forest stand located in the
Kirkwood forest. The soil on this site has
an unavailable water content (i.e., held
with a tension greater than -1.5 Mpa) of
between 25 and 50 mm of water up to 1.0
m soil depth (based on a column of soil).
Soil water balances were reconstructed
from weather data from Blind River for
1970, a year with abundant precipitation.
Soil drainage has a great influence on
the available moisture (Figure 3.2). For
every 10 mm of rain, more than 50% infiltrates the soil, the rest is lost to runoff and
evaporation. As the amount of rain per
rainfall increases, the proportion of infiltration increases. Therefore, although the
soil is supplied abundantly with water, it
does not have the capacity to retain this
water and supply it steadily to trees. In
fact, after an abundant rain, water is easily
available for only two to three days. In
Ontario’s forests, except for the clay belt,
available water varies, approximately,
between the limits indicated by Figure 3.2.
However, in large areas in northwestern
Ontario, where soils are shallow and stony,
they are also more prone to water deficit.
The expected increase in annual variability
of rains (Bolin et al. 1986), may result in
more frequent and longer occurrences of
soil water stress.
Soil hydraulic conductivity (the rate of
water movement in a soil), which significantly affects soil water regime, depends
greatly on soil texture — the coarser the
soil, the greater the conductivity. While
organic matter significantly improves soil
water retention by reducing hydraulic
conductivity, unfortunately, the organic
layer of most soils in Ontario (with the
Figure 3.1. Rainfall in 1970 in Blind River, Ontario; estimated potential evapotranspiration (ETp) for actual temperatures (ETp0), and with 2oC (ETp2) and 4oC (ETp4) warming.
exception of peatlands) is thin. Site
disturbances, especially hot ground fires
and some mechanical site preparation
techniques, can greatly reduce the thickness of the soil organic layer, leading to
increased soil water deficits. Sites with
coarse-textured soils overlain by thin
organic layers are most susceptible to
problems with water availability. Organic
matter can be enhanced silviculturally by
promoting hardwoods.
The forest species that grow in Ontario, and whose distribution and productivity is going to be affected by climate
warming include the commercial species
black spruce, jack pine, and red pine.
Typically, these are shallow-rooted species,
which depend solely on moisture available
in the first metre of soil. At present, these
species are productive because rains are
frequent or humidity is high, which either
re-supplies the soil with moisture at short
intervals or results in low ADE, respectively. In a progressively warmer scenario,
with increased evapotranspiration but
similar soil water holding capacity, these
species are likely to suffer moisture stress
more frequently and for longer periods.
The expected increase in climatic variability may make the situation worse, because
large rainfalls, likely to occur under this
scenario, do not greatly improve the water
regime due to the large amount of precipitation lost to infiltration. These stands will
first be affected in terms of reduced productivity, and then, in the event of a prolonged drought with high ADE, mortality
may occur. Reduced stocking through
thinning is a potential means of redistributing soil moisture to prolong the productive life of such stands. In contrast with
shallow rooted species, deep rooted ones
have the advantage of being able to absorb
water from greater soil depths. Deeply
rooted species are expected to be better
adapted to the increased ADE and soil
moisture deficits that may occur in some
areas of Ontario.
Figure 3.2. Rainfall in 1970 in Blind River, Ontario, and estimated infiltration and soil water storage for soils with 25
and 50 mm reserve.
Across Ontario, the influence of
climate warming on the soil water balance
will be affected by (i) air circulation patterns, (ii) regional soil characteristics, and
(iii) inherent natural variability. On typical
forest sites in the next century, in my
opinion we might expect that in southwestern Ontario existing forest ecosystems will experience moderately increased moisture stress. Over a 30- to 50year time frame, soil moisture stress
should be controllable through thinning.
In the clay belt, water availability is expected to remain high (Section 2). On
some low-lying peatland sites in northeastern Ontario, where water tables are
already high and drainage impeded, the
forecasted 10 to 20% projected increases in
precipitation (Section 2, Figure 2.2) may
raise the water table enough to cause
flooding in some stands. On these sites,
drainage could be used to preserve existing stands. In the boreal forests in northwestern Ontario, where soils are shallow
over shield or till deposits vegetation is
expected to experience high levels of soil
moisture stress as a result of climate
change. This area is already prone to
forest fires, which are predicted to increase under a warming scenario (Section
6). The establishment of mixed coniferhardwood forests should be encouraged
to promote the buildup of forest litter and
humus, which will improve soil moisture
retention.
Section 4.
Insects and Climate Change
Taylor Scarr, Forest Management Branch,
Ministry of Natural Resources
Insect outbreaks have substantial
effects on Ontario’s forests. Outbreaks
such as spruce budworm and gypsy moth
often occur over large areas and can cause
widespread tree mortality (Hardy et al.
1986). Together with fire they are the
major disturbance influencing the successional patterns in both the Boreal and
Great Lakes–St. Lawrence forests
(Fleming and Candau 1997). They further
affect the nutrient and biogeochemical
cycles of forests through the conversion of
tree biomass to other trophic levels of the
ecosystem.
If the predicted changes in climate
occur, resulting in increases in mean
annual temperature and more extreme
weather, there will be direct effects on
insect population dynamics, which in turn
will affect forest stand structure, composition, and function. The greatest effect of
the predicted climate change is likely to
be on the insect disturbance regime; that
is, the frequency, duration, and severity of
population outbreaks (Fleming 1996).
Because fire regimes are often intricately
linked with insect disturbance, changes in
insect outbreak patterns will cause
changes in the fire regimes, which together will affect the composition of the
forests of Ontario (Fleming and Candau
1997).
The challenge caused by climate
change for forest managers is that it will
be very difficult to predict which tree
species will form the future forest in a
region, and which insect species will
become the major disturbance forces in
that new forest (Sandberg 1992). Each tree
and insect species must be considered
individually in terms of its response to
climate change (Logan et al. 1995), yet each
will influence the other. The uncertainty
over future forest condition makes it difficult to project sustainable timber supplies
and to determine how to mitigate the effects of climate change to maintain a
healthy forest that can meet society’s demands (Fleming and Volney 1995).
Tree species will respond differently to
climate change (changes in the average and
extremes in temperature, precipitation,
weather events, CO2 concentration, fire,
insect outbreaks, disease). In the southern
part of current ranges, tree regeneration
rates are expected to decrease while senescence rates are likely to increase (Fleming
1996). Local extinction may result if an
outbreak of an insect occurs that attacks
older trees, driving the tree population
below the threshold at which it can sustain
itself. For northerly sites, tree regeneration
rates should increase, while senescence
rates should decrease. The result, again, is
destabilization of the ecosystem. As described by Fleming (1996), "chance, historical factors, and threshold effects" will
significantly affect the condition of the
forest ecosystem as this destabilization
occurs.
Climate change is expected to have
several effects on insect-tree interactions:
• insects that are currently pests may no
longer remain so depending on their
response, as well that of their host trees,
to climate change (Hedden 1988);
• tree growth rates may increase under
warmer temperature conditions, but
poikilothermic insects may respond more
• some insect pheromones may be less
stable at higher temperatures, reducing
the species' reproductive potential and
competitiveness (Hedden 1988);
mortality, increased fecundity, and decreased effects of pathogens (Fleming
1996).
These effects of climate change are not
mutually exclusive, and will be influenced
by effects of climate change on trees and
their competitiveness with other trees and
plants, other disturbance regimes such as
fire and extreme weather, the speed at
which climate change occurs, and chance.
The result of these effects and the
destabilized ecosystem will be individualistic movement of parts of the system in
response to climate change. For forest
managers, this inherent uncertainty provides only generalizations (Hedden 1988):
• shortening stand rotations to reduce the
period of vulnerability and increase
vigour;
• the increased CO2 concentration may
enable trees to produce more carbonbased antifeedants, increasing the resistance of some tree species to some insects;
• aggressive tree breeding to increase
resistance to insect pests or to speed
adaptation to the emerging climate (see
Section 8);
• increased CO2 concentration may increase the carbon to nitrogen ratio in tree
foliage, resulting in increased feeding by
defoliators to obtain sufficient nitrogen;
• controlling competing vegetation (e.g.,
via thinning, weed control) to reduce
stress to regenerating trees and help
produce desired species composition in
the future forest (see Section 9);
efficiently, giving them a competitive
advantage (Fleming and Tachell 1995);
• tree growing seasons may be extended,
but insect species may increase their
number of populations per year;
• some insect species may become pests if
the new temperature or moisture regimes are outside the optimum range for
their parasites, predators, or pathogens,
allowing the host species to escape these
natural controls;
• some insect species will be adversely
affected by effects of climate change on
diapause requirements;
• increased drought could increase sucrose
concentration in foliage, favouring insects;
• increased drought can lead to earlier leaf
stomatal closure, increasing temperature
and decreasing relative humidity of the
leaf outer microclimate, resulting in
increased insect growth rates, decreased
• sanitation cutting to encourage healthy
stands;
• minimizing adverse disturbances during
harvesting to reduce stress;
• using insecticides to control damaging
insects and reduce timber volume losses.
Section 5.
The Impact of Climate Change on Fungi in the
Forest Ecosystem
Sylvia Greifenhagen, Ontario Forest
Research Institute, Ministry of Natural
Resources
Of the many predicted effects of
global warming, a rapid increase in average temperatures (1 to 3.5°C over the next
century), combined with increased
drought periods and increased frequency
of catastrophic weather events, will have
the most significant impact on fungal
communities in Ontario’s forest ecosystems. Soil microbes, of which fungi are a
major component, are the drivers behind
many of the processes occurring below the
forest floor. Ecosystems are regulated by
the rates at which soil processes occur.
These below ground systems will be critical determinants of ecosystem response to
climate change (O’Neill 1994). The functional biodiversity of an ecosystem, especially of below-ground organisms, plays
an important role in regulating the impacts
of disease by causing disruptions in ecological continuums, thereby limiting disease outbreaks. Climate-caused changes in
functional groups may substantially affect
this regulatory role. The effects of global
warming on tree diseases and the entire
soil microbial population, including
mycorrhizae, will vary with fungal species,
the biotic forest community, the abiotic
environment, and interactions and associations between these components.
Forest Tree Diseases. Over 20 million
cubic metres of timber are annually depleted by diseases in Ontario’s forests
(Gross et al. 1992). Increases in incidence
and severity of diseases because of global
warming will substantially affect the
timber resource. Many of the most impor-
tant diseases in Ontario’s forests, such as
root diseases, stem decays, and declines,
require a stressed host before infection or
disease expression occurs. When a tree is
stressed, less energy is available to sustain
the physiological processes critical to
disease resistance, as more energy is
allocated to life-sustaining processes
(Wargo and Harrington 1991). Diseases
respond to stress in plants in various
ways such as increased incidence or
severity. When stressed, a normally
resistant tree species may become susceptible to a certain disease, broadening the
host range of the pathogen. Stress caused
by an increase in the number and severity
of catastrophic weather events, especially
drought, may increase disease susceptibility, especially where plants are not physiologically adapted to a site or are near the
limits of their range (McDonald et al.
1987). For example:
• above average temperatures, possibly
associated with soil drying and fine root
death, have played an important role in
sugar maple decline (Cannell et al.
1989);
• in one study, a 2°C increase in soil temperature above the optimal temperature
for growth of white birch (i.e., 18.5°C)
caused substantial fine root death
(Redmond 1955);
• red spruce dieback may be associated
with summer drought and a general
increase in temperature since the 1800’s;
• parasitism by Armillaria root disease
increases during periods of drought,
while wet periods favour its saprophytic
(i.e., living on dead organic matter) role
(Nechleba 1927);
• certain Armillaria species primarily
attack conifers, but will attack
hardwoods weakened by ice damage to
the crowns (Dance and Lynn 1963).
Drought-induced stress will be most
severe on the shallow soils of the boreal
forests of northwestern Ontario, and incidence and severity of Armillaria ostoyae, the
most common root decay fungus in the
boreal forest, may increase on these sites.
An increase in the host range of this stressinduced disease may occur in the hardwood and mixedwood forests of eastern
and northeastern Ontario.
Soil Microbes. Soil contains the largest
terrestrial pool of organic carbon (Batjes
1996). Changes in the abundance and
diversity of soil microbial communities
and functional groups as a result of climate
change may have far-reaching impacts on
many ecosystem processes. For example,
soil microbes, including fungi, are responsible for carbon and nutrient cycling and
formation of soil structure in forest ecosystems. Climate change may affect the rates
of decomposition or organic residues in
soil, which will influence the availability of
nutrients required for plant growth. Because of the intricate relationships that
exist between above-ground plants and
soil biota, changes to any one component
can have far-reaching effects throughout
the ecosystem.
Although the effects of climate change
on soil microbes will vary substantially
with site and microbial species, in general,
drought and fire reduce soil microbial
diversity, at least in the short term. Reduced diversity may have adverse effects
on forests, because a highly diverse
mycoflora could be important to the ability
of plants to adjust to climate change
(O’Neill 1994). Increased atmospheric CO2
levels may also significantly affect soil
microbial processes. Concentrations of
nitrogen and other nutrients in plants may
decrease as atmospheric CO2 levels in-
crease, resulting in a gradual decrease in
degradability of plant residues by microbes
(Couteaux et al. 1995) and an accumulation of
nutrient-poor organic matter (Lekkerkerk et
al. 1990). Mycorrhizae are a highly specialized
group of soil fungi that form symbiotic associations with plant roots, enhancing plant
nutrition, water uptake, growth, and stress
resistance (Molina et al. 1992). As with soil
microbes generally, mycorrhizal associations
are affected by soil moisture and temperature;
the effects of climate change may, therefore,
vary with fungal and host plant species
(Monz et al. 1994). Certainly the complexity of
plant-microbial-environment interactions
make the prediction of climate change effects
extremely difficult! However, under the
assumed climate change scenario, the following events may occur:
• fungi that are favoured by disturbance will
become more prevalent (Miller and Lodge
1997);
• the rate of litter decomposition may rise by
up to one third its present rate if annual
temperatures rise by 3°C (Cannell et al.
1989, Schimmel 1995). Marginal soils should
become more productive, at least in the
short term, where drought is not a limiting
factor;
• long-term, repeated drought will cause
fluctuations in the microfungal biomass,
reducing the availability of nutrients and
thereby limiting plant growth (Lodge et al.
1994). Drought effects may be mitigated by
mycorrhizae, which enhance stress resistance and nutrient uptake in trees (Miller
and Lodge 1997);
• the migration of many pioneering tree
species will depend on the successful migration of their host-specific mycorrhizae
(Meyer et al. 1982);
• the productivity of boreal forests in the clay
belt of northeastern Ontario, where water
availability should remain adequate (see
Section 2), could benefit from an increase in
the rate of litter decomposition caused by
increased temperatures.
Interactions between climate and
biotic systems are extremely complex
(Ojima et al. 1991) and understanding the
potential impacts of climate change on
fungi in forest ecosystems is a great challenge. Information is needed on how
specific fungi and fungal communities
interact with each other, with the forest
ecosystem in general, and with the changing global environment. Stress-hostpathogen relationships and interactions
need to be identified (Wargo and
Harrington 1991). A better understanding
of microbial processes, microbial diversity,
and variations with site, forest composition, temperature, and moisture in Ontario’s forest soils will provide information
needed to predict microbial responses to
altered environmental conditions. More
information is needed on the ecological
specificity of mycorrhizae and their successional variation (Molina et al. 1992).
This knowledge will improve our understanding of the roles fungi play in community development and ecosystem stability
(Molina et al. 1992), and can be used to
develop sound forest management practices for a period of rapid global change.
Section 6.
The Impact of Climate Change on Forest Fires
and Forest Fire Management in Ontario
Robert S. McAlpine, Aviation, Flood and Fire
Management Branch, Ministry of Natural
Resources
There is strong consensus that climate
change will increase fire activity in Ontario
(Simard 1997). This increase in fire activity
can be attributed to three of the implications
of global climate change: (i) increased frequency and severity of drought years; (ii)
increased climatic variability and incidence
of extreme climatic events, and (iii) increased
spring and fall temperatures.
The most influential implication of
climate change for forest fire management is
the predicted increased frequency and severity of drought years. Clearly, during years of
much lower than normal rainfall, fuel moisture levels decrease and the forest is predisposed to fire. This is manifested as an increase in the forest fire weather severity
rating (Williams 1959, Van Wagner 1970,
1987)—an integration of weather factors
(temperature, relative humidity, wind speed
and precipitation) over periods of various
lengths (daily, monthly, seasonal, etc.). Fire
weather severity is an objective yardstick for
comparing weather (and hence the risk of
forest fires) from site to site and from year to
year (Van Wagner 1970). Flannigan and Van
Wagner (1991) estimated that climate change
would produce a 40% increase in fire
weather severity in Canada, resulting in a
similar increase in area burned. Stocks et al.
(1998) extended this with results from refined climate change models to predict
altered patterns of fire weather severity in
Canada.
Figure 6.1 uses methods similar to those
of Stocks et al. (1998) to show the impact of a
doubling of atmospheric CO2 on the seasonal
fire weather severity in Ontario. The figure
shows a general increase in severity across
the province, with some larger changes in
the extreme west (Kenora area) and southeast (Ottawa area) of the province. The most
pronounced changes will occur during June
and July and to a slightly lesser extent, May
(Figure 6.2). While August and September
also show a predicted increase in fire
weather severity, it is not as conspicuous.
The area near Quetico Park (south west of
Thunder Bay) changes very little in any
month. In contrast, the fire weather severity
around Sudbury and for much of Southern
Ontario is expected to increase to near prairie-like conditions (see Figure 1 in Stocks et
al. 1998 for comparison).
A second major element of climate
change that will affect fire management is
increased variability of the climate and
increased incidence of extreme climatic
events. Fire “flaps” result from a short-term
increase in fire danger caused by two or
more weeks without appreciable rain coupled with an ignition source (Canadian
Forestry Service 1987). This kind of climatic
event could easily be offset by episodic
cooler moist weather and would therefore
not appear in the monthly fire weather
severity plots of Figures 6.1 and 6.2. With
increased climatic variability, the incidence
of these short term peaks in fire danger will
become more prevalent. In addition, Fosberg
et al. (1990) and Price and Rind (1994) predict that climate change will be accompanied
by increases in lightning activity, the cause
of 80% of the area burned in Ontario. Typically, large fire runs (and hence area burned)
are the result of a few days of extreme fire
weather. With increases in these extreme
events along with an increase in lightning
activity, an increase in area burned can be
expected.
A third element affecting forest fire
activity is the predicted increase in spring
and fall temperatures, which extends both
the growing and forest fire seasons. Wotton
and Flannigan (1993) estimate that climate
change will extend fire season length in
Ontario by 25 days (a 16% increase). Figure
6.2 shows a slight increase in fire weather
severity in September, however the monthly
resolution of this map is too long to show the
predicted increase in fire season length. In
addition, data for the month of April were
unavailable. April may show a larger increase in fire weather severity than September, as the trend from Figure 6.1 shows larger
changes in fire weather severity early in the
season.
The increases in drought years, extreme
climatic events, and fire season length indicate that climate change will result in longer
fire seasons, with greater fire load and
greater incidence of extreme fire load years.
Trends since 1985 indicate increased forest
fire activity in Ontario. Whether this is the
result of climate change, increased weather
variability, or some other factor is difficult to
assess. In any case, if the current protection
levels are to be maintained, and a increases in
area burned minimized, the changes in the
environment brought on by climate change
will necessitate increases in fire management
expenditures. How to best minimize the total
fire management investment and provide an
acceptable level of fire protection will be the
challenge of the next few years.
Forest fires are a natural part of the
global carbon cycle. Increased fire activity
will release more CO2 into the atmosphere,
adding to the greenhouse effect. Table 6.1
shows carbon emissions from forest fires in
Ontario based on estimates of fuel volume
and carbon emission factors published by
Stocks (1990, 1998, pers. comm.).
Values in Table 6.1 are presented by fire
management zone. The intensive zone corresponds to those areas of central and Northern
Ontario containing major population centers,
recreational areas, and forest industry. Fires
in the intensive zone are aggressively detected and suppressed (note the smaller
average fire size). The measured zone encompasses a broad east-west band north of the
intensive zone, and covers areas of moderate recreational use and future wood supply. Most fires are aggressively detected and
attacked, however if initial attack fails, the
fire is assessed to determine if suppression
action will continue as aggressive, moderate, or minimal. The extensive zone represents the far north of Ontario where most
fires are allowed to burn unsuppressed
unless specific resources are at risk. Estimates of carbon emissions from prescribed
fire, largely from burning of logging debris,
are also provided in Table 6.1.
The combined CO2 emissions from
wildfire and prescribed fire is in excess of
3.5 Terragrams (Tg) of CO2 (3.5 million
tonnes). This constitutes about 2% of Ontario’s total CO2 emissions. Increases in the
level of protection in the measured or extensive zones of Ontario (the primary CO2
production zone on a per fire basis) would
reduce these emissions. To demonstrate, if
the entire area of the measured and extensive zones were converted to intensive
protection, the average forest fire size in
these zones would perhaps be reduced to
that of the current intensive zone. This
would reduce carbon emission by 2.38 Tg
CO2. However, this quantity of sequestered
carbon cannot be protected ad infinitum.
The carbon will be eliminated from the site
either by decomposition or large conflagration type fires (due to excessive fuel loads)
unless it is removed from the site and sequestered elsewhere (e.g., wood products).
The change in level of protection to reduce
carbon emissions from wildland fires
would change the fire return interval of a
large part of Ontario’s wilderness. The
ecological ramifications and economic costs
of this change in fire return interval must be
carefully considered.
Table 6.1. Annual average greenhouse gas emissions from Ontario wildland forest fires and prescribed burning from
1989 to 1996.
Fire
management
zone/
C02 source
Annual
area
burned (ha)
Average
fire size
(ha)
Average
no. fires
annually
CO2
emission
(tonnes)
CO2
emissions
(tonnes)
Aerosol
emissions
(tonnes)
Percent
of total
emissions
Intensive
46, 366
36
1,279
515,820
52,162
5,274
15
Measured
34,071
187
183
379,037
38,330
3,876
11
Extensive
211,348
1658
128
2,351,248
237,767
24,041
67
Prescribed
fire (slash
piles)
not applicable
36,000 kg1
17,000 piles
272,340
12,255
2,785
8
291,785
1,881
1,589
3,518,445
340,514
35,976
100
Total
estimated average weight of wood per slash pile
1
Section 7.
Plant Physiological Responses to a Changing
Environment
Stephen J. Colombo, Ontario Forest Research
Institute, Ministry of Natural Resources
The physiological function of commercial tree species is the basis for their
productivity and the wood-based economic benefits derived from Ontario’s
forests. In addition, the diversity of forest
plants depends on physiological attributes
that allow different species to survive and
thrive despite environmental stresses. If
climate change alters the occurrence of
plant physiological stress then the commercial benefits derived from forests and
the biological diversity of forest ecosystems in Ontario will also be changed
(Joyce et al. 1990).
Plant physiology is one means by
which environment is translated into
effects on forest ecosystems, at first by
action on the physiology of an individual
plant, and as a consequence on plant
populations and communities. Forest
vegetation is directly affected by temperature, the concentration of CO2 in the air,
mineral nutrition, and water supply, all of
which are expected to change in Ontario in
coming decades (Walker and Steffen 1997).
In addition to such direct effects, climate
also affects forest plant communities
indirectly through plant-to-plant competition for site resources (e.g., water, light,
nutrients). An understanding of the direct
and indirect effects of climate change on
plant physiology is needed to predict
climatically induced changes in forest
productivity, forest health, and
biodiversity.
Table 7.1 summarizes some of the
effects of increased atmospheric CO2,
temperature, and moisture stress due to
more frequent and prolonged droughts on
plant physiological processes and
growth. Rates of photosynthesis are
increased by higher concentrations of
CO2 and warmer temperatures (Battaglia
et al. 1996); however, the magnitude of
such increases is proportional to growth
rate (Tissue et al. 1996) and nutrient
supply (Drake et al. 1997). Stomatal
conductance (which is related to the rate
of water loss from leaves by transpiration) is reduced by increased CO2 and as
an aftermath of drought, but increased
by warmer temperatures. Water use
efficiency (the ratio between the rate of
photosynthesis and the loss of water
through transpiration) increases with
elevated CO2 and drought, but decreases
if conditions are warm and very humid.
Phenology (the timing of bud burst,
flowering, and other growth processes)
is increased by warmer temperatures but
delayed by drought and elevated atmospheric CO2 (Murray et al. 1994). Warmer
temperatures in the spring lead to earlier
bud burst, which potentially exposes
new growing shoots to freezing damage
(Colombo 1998). Warmer temperatures
in the fall may delay frost hardening and
warmer winters could reduce the
amount of chilling plants receive; insufficient chilling may not completely overcome dormancy of some species in
southwestern Ontario, which would
delay bud burst resulting in a shortened
growing season. Drought, in comparison, can shorten the growing season by
causing plants to cease growth earlier in
the summer. While each climate change
factor has an independent effect on plant
physiology, in many cases there are potential interactions that produce complicated
effects and modified plant responses. In
general, more information on such interactions will allow us to better predict the
effects of climate change on plant physiology.
Our understanding of plant responses
to the environment is largely based on
short-term experiments conducted in
controlled environments, in which only
one or two factors were varied, and small
or young plants were used. While this is a
logical first step in attempting to understand responses to climate change, caution
is required when extrapolating plant-scale
results to ecosystems, because of the oversimplification these experiments entail.
Scaling effects frequently alter the way
finer scale events (e.g., leaf or plant level
responses over short time spans) translate
into larger scale results (e.g., stand or
community function and structure over
long time spans) (Körner 1993). Direct
observations of plant behaviour and interactions in forest plant communities are
required to link physiological processes to
long-term reactions of forest ecosystems.
Information obtained from studies of
physiological behaviour in a plant community is required to develop management
options to mitigate the negative effects of
climate change. There is probably more
value in controlled environment studies
that are planned based on observations of
plant behaviour in a community; in this
top-down approach it is possible to target
a particular species and to dis-aggregate
the effects seen at higher levels of organization in terms of species interactions and
primary physiological processes.
All areas of Ontario will experience a
doubling of atmospheric CO2 in the latter
half of the next century and this is expected to increase temperatures, with the
greatest temperature increase predicted in
northwestern Ontario (see Section 2).
Precipitation in Ontario is expected to
decrease in the northwest and south and
increase in the northeast (Section 2). The
warmer and drier conditions expected in
northwestern and southern Ontario will
favour species that are more tolerant of
periodic drought (Schindler 1998). Based
on their physiology, more frequent and
severe drought will affect the growth of
the following tree species in northwestern
Ontario increasingly in the order: jack pine
(least negatively affected), white spruce,
aspen, and black spruce (most negatively
affected).
Relative physiological responses of
competing forest plant species to climate
change can be as important as absolute
species responses. “Response hierarchies”
based on plant physiological responses to
increased CO2, have been developed by
Körner (1993). In general, increased CO2
will favour evergreen species less than
deciduous woody species, which will in
turn be less favoured than perennial species (e.g., fireweed, raspberry, and
grasses). Annual herbaceous species will
be most favoured by increased CO2. Elevated CO2 will favour seedlings more
than young trees and young trees more
than old trees. Late successional species
(e.g., maple, yellow birch, white spruce,
white pine) will be less favoured than
early successional species (e.g., aspen,
poplar, oak, jack pine, black spruce). Species with small or infrequent seed and fruit
crops (e.g., black spruce, aspen) will be
less favoured than species with large
frequent seed and fruit crops (e.g., oak,
white pine). Nitrogen-fixing species will be
more responsive to elevated CO2 than nonnitrogen-fixing species, and mycorrhizal
species more so than non-mycorrhizal
species. In terms of forest sites, elevated
CO2 levels will favour plants growing on
non-nutrient deficient and warm soils over
those on nutrient deficient and cold soils.
Similar response hierarchies are needed to
understand the effects of increased temperature and drought on Ontario forest
species.
The rise in winter temperatures across
the province should help to expand the
potential range of less frost hardy species
from the Great Lakes-St. Lawrence forest
region into what is now the southern
boreal forest (Reed and Danseker 1992). In
northwestern Ontario, where drought will
be more common, drier conditions combined with warmer winter temperatures
would favour the northern expansion of
the ranges of red oak and red pine, while
the range of sugar maple could also move
north but be limited to moister sites. In
northeastern Ontario, where warmer
winter temperatures may be accompanied
by increased summer precipitation, the
southern range of the boreal forest and the
northern range of the Great Lakes-St.
Lawrence forest should move north.
Within perhaps 100 to 200 years, increased
winter temperatures in southern portions
of northeastern and northwestern Ontario
may create conditions favourable to oakhickory forest species that are presently
restricted to Minnesota, Wisconsin, and
southern Michigan.
Increased, with possible feedback
reductions due to resource limitations,
(e.g., nutrient supply)
Decreased (usually)
Slightly decreased
Reduced
Increased
Increased
Increased
Shortened growing season due to
delayed bud burst in the spring and
earlier bud set in the fall
• Increased growth rates
• Reduced stomatal density in many
species
• Increased root growth (species
dependent) and greater allocation to
stemwood volume
Increased drought tolerance due to
stomatal closure
Photorespiration
Dark respiration
Stomatal conductance
Light use efficiency
Water use efficiency
Nutrient use efficiency
Phenology
Carbon partitioning/
plant structure
Susceptibility to stress
Elevated CO2
Photosynthesis
Physiological process
Potentially increased damage from
spring and winter freezing
• Increased growth rates
• Earlier bud burst and flowering
• Earlier bud break
• Later development of winter frost
hardiness
• Potential lack of chilling for dormancy
in southwestern Ontario
No effect
Reduced at warmer temperatures (if
vapour pressure deficit unchanged)
Increased susceptibility to other stresses
(e.g., acid precipitation, ozone) and
insects and disease
• Increased flowering and seed
production
• Increased root growth/reduced shoot
growth
• Reduced leaf area
Earlier cessation of shoot elongation
May be increased
Increased
Decreased
Reduced
Increased at temperature up to 30-350C
No change
Increased
Increased
Reduced during drought and for a
period following drought relief
Increased drought severity and
frequency
Increased
Increased
Increased but with possible feedback
reductions or resource limitations
Warmer temperature/Longer
frost-free season
Table 7.1. The effects of three aspects of climate change (increased atmospheric CO2 concentration, warmer temperature, and drought) on selected important plant physiological processes.
Section 8.
Genetic Implications of Climate Change
Marilyn L. Cherry, Ontario Forest Research
Institute, Ministry of Natural Resources
The genetic makeup of plant and
animal species in Ontario will be affected
by the consequences of climate change,
including increased temperatures and CO2
levels, changes in moisture patterns,
higher occurrence of extreme weather
events and forest fires, changes in growing
season length, and changes in insect and
disease occurrences, due to the selection
pressure exerted by these effects. It is
generally believed (e.g., Peters 1990) that
species which are presently widespread
will experience drastic shifts in range
boundaries and undergo certain losses of
genetic variation and some population
extirpation, while smaller, localized species may undergo severe reductions in size
or possibly extinction. Effects of climate
change are not expected to be smooth and
gradual; instead, they will involve thresholds to limits of tolerance (Vitousek 1994).
Predictions as dire as a 37% decrease in the
extent of the boreal forest with a 3°C global
temperature increase have been made
(Peters 1990). However, as the extent and
distribution of genetic variability is poorly
known for most forest species, it is difficult
to predict how populations will change in
relation to the uncertainties surrounding
global warming.
General plant and animal responses to
changes in the environment include
phenotypic plasticity, migration, and
evolutionary change (Stettler and
Bradshaw 1994). Generalist species are
those in which a typical genotype is able to
flourish under a wide range of environmental conditions. Phenotypic plasticity,
the ability to acclimate in response to
environmental cues, is a trait of generalist
species, and may itself differ between
genotypes of a species. Phenotypic plasticity will allow for survival of individuals
that may not be the most genetically fit in a
particular environment (Eriksson et al.
1995).
Migration rates following climate
change will differ for every species, depending on how efficiently they are able to
disperse and whether migration corridors
exist between favourable environments
(Peters 1990). Species assemblages will
dissociate due to differing rates of migration, and new species combinations will
form (Peters 1990; Stettler and Bradshaw
1994; Walker and Steffen 1997). Physical
barriers to dispersal, such as the Great
Lakes, will impede migration. Dispersal in
some animal species will be affected by
social requirements (such as territoriality
and annual bird migration) (Harris et al.
1984). Migration in plant species will be
affected by seed and pollen quantities,
dispersal rates (Table 8.1), and whether
conditions are favourable for fertilization,
seed production, or vegetative propagation.
Evolutionary adaptation to new
climate conditions can only occur where
sufficient genetic variation exists to allow
selective forces to discriminate between
adaptive and maladaptive traits (Harris et
al. 1984). Once an allele (one form of a
given gene) is fixed (only that one form of
the gene is present in a population) or lost,
only mutation or immigration can restore
genetic variability. Adaptation may occur
more rapidly in species with shorter life
cycles, as long as conditions are favourable
for reproduction, than in longlived species
such as trees which will undergo a time
lag response to changing conditions
(Brubaker 1986). Responses within
a species’ natural range may not be uniform, but might vary from region to region
(Rehfeldt et al. 1998). Due to genetic constraints to adaptation and time lags in
adapting, local populations are not always
the fittest (Matyas 1994). Certain species
unable to acclimate or adapt to changing
climatic conditions may not be able to
disperse rapidly enough to avoid extinction without human intervention.
Species most susceptible to changes
in climate are those that are localized,
highly specialized, or poor dispersers
(Peters and Lovejoy 1992). Populations
most at risk are isolated or peripheral
communities at the edge of a species’
range, and those that occupy montane,
alpine, arctic, or coastal sites (Peters and
Lovejoy 1992). Species considered most
sensitive to past climate change showed
evidence of latitudinal and elevational
shifts in response to changing conditions
(Nowak et al. 1994).
An increase in atmospheric CO2 will
increase growth of some species at the
expense of others (Peters 1990). Under
conditions of increased CO2, selection may
favour genotypes with an ability to compete for limiting resources other than CO2
(Bazzaz et al. 1995).
Population reductions are expected
along the southern edges of a species
range and inland, away from the moderating effects of large bodies of water, as a
result of increasing temperatures and
moisture stress (Peters 1990; Nowak et al.
1994). The latter is expected in northwestern Ontario, where drought is expected to
become more frequent and severe (see
Section 2). Population reductions will also
occur if populations shift upwards in
elevation; however, this is unlikely to have
a major effect in Ontario. Plants subjected
to high stress, such as those at the edge of
a range, will be more susceptible to insects
and pathogens (Ledig and Kitzmiller
1992), which have the advantage of being
able to adapt to changing conditions more
rapidly because of their much shorter life
cycles.
With range reductions, population
fragmentation will occur, and inbreeding,
with its inherent loss of genetic variation,
will increase as population size decreases.
If selection due to climate change operates
Table 8.1. Relative range size and seed dispersal of some Ontario tree species.
Species
Range size
Mode of reproduction
Seed dispersal
jack pine
large
seed
poor
red pine
small
seed
good
eastern white pine
medium
seed
medium
black spruce
large
seed, vegetative
medium
red spruce
large
seed, vegetative
medium
white spruce
large
seed, vegetative
good
balsam fir
large
seed
medium
sugar maple
medium
seed, vegetative
good
red maple
medium
seed, vegetative
good
red oak
medium
seed, vegetative
poor
trembling aspen
large
seed, vegetative
very good
differentially on subdivided populations,
then the variation between the
subpopulations will increase, and discrete
ecotypes may be formed (Harris et al.
1984). The length of time that a population
remains at reduced numbers will have a
greater impact on reduction in genetic
variability than the actual number of
individuals in the isolated population
(Harris et al. 1984). Whereas highly heterozygous individuals (those with different
alleles in a given gene pair over many of
the gene pairs) can generally tolerate a
broader range of environmental conditions, perhaps due to the differing alleles
being advantageous under differing conditions (Harris et al. 1984, Ledig and
Kitzmiller 1992), favourable complexes of
genes that have adapted together will be
reduced with inbreeding.
The ability of a species to withstand
inbreeding and selfing is important in
isolated populations (Peters 1990).
Populations with reduced reproductive
potential or under low levels of selective
pressure will carry deleterious, potentially
harmful genes for a longer period; with a
high reproductive rate and intense selection, fewer adverse effects of inbreeding
will occur (Harris et al. 1984). If dramatic
climate change occurs over a short time
span, selective pressures will be intense,
and hence high reproductive rates will be
advantageous in isolated populations.
Populations in which inbreeding has
occurred prior to fragmentation are expected to carry fewer deleterious genes
and will not be as adversely affected by
subsequent inbreeding (Harris et al. 1984).
Species that reproduce both by both sexual
and asexual means will be less sensitive to
climatic change (Brubaker 1986), whereas
species that rely on asexual reproduction
will be less likely to adapt (Table 8.1)
(Harris et al. 1984).
Forest tree species generally have high
levels of genetic variability and gene dispersal rates (Brubaker 1986; Stettler and
Bradshaw 1994). An exception is red pine
which demonstrates low levels of genetic
diversity, probably because populations
were severely reduced during the last
glaciation. Trees also carry a high number
of deleterious genes (Stettler and
Bradshaw 1994). Due to their longevity,
trees withstand a broad range of climatic
variation per generation, and some species
have demonstrated phenotypically plastic
responses to environmental change.
The boreal forest of northern Ontario
has lower levels of biodiversity, with fewer
plant and animal species, than the deciduous forests of southern Ontario (Dudley et
al. 1996). Rare, threatened, and endangered species are often found on
nonforested sites (Harris et al. 1984), and
may be especially dependent on habitat
characteristics (Eriksson et al. 1995). Predictions for the effects of climate change
on forest habitat in Ontario are varied and
sometimes conflicting. However, most
models of tree migration predict a northward movement of coniferous species,
particularly spruce, and a corresponding
replacement by hardwood tree species
such as maples and oaks (Joyce et al. 1990;
Slocum 1995).
A climate change model based on
provenance trial data (Matyas 1994) predicts a decline in the growth and competitive ability of jack pine at the southern
limits of its distribution. Under controlled
climate experiments, some generalist
genotypes for growth traits were identified
for seedlings of this species (Cantin et al.
1997). Carter (1996) predicts a decrease in
growth due to warmer growing conditions
in white ash, yellow birch, black cherry,
balsam fir, tamarack, white spruce, jack
pine, and eastern white pine, and increased growth in red maple and green
ash. Other models predict a loss of balsam
fir, eastern hemlock, and sugar maple from
the Great Lakes region (Joyce et al. 1990).
It is undoubtedly premature to prescribe a northward transfer of species until
the extent of climate-induced changes can
be more accurately predicted. However, it
would be wise to revisit old provenance
tests to determine current limits to transferability.
Better estimates of the amount and distribution of genetic variation within species
are needed before the guiding principles
discussed above can be applied to each
species. Selection for pest resistance is also
recommended, as pest infestations are
likely to worsen (see Section 4). Conservation plans for rare, threatened, and endangered species should be developed and
implemented before population levels of
these species decrease irreversibly. Such
plans should include development of
dynamic appraoches that will promote
increases in genetic variance and future
adaptation, such as the multiple population breeding system proposed by
Namkoong (1984). Genetic implications of
global warming cannot be considered
alone; changes in gene frequencies will
depend on many factors, some of which
are the intensity of selection pressures,
responses of physiological processes, and
changes to forest succession, competition,
and pest incidence.
Section 9.
Climate Change and Forest Vegetation
Dynamics in Ontario
William C. Parker, Ontario Forest Research
Institute, Ministry of Natural Resources
Forest succession may be viewed as
the recovery of forest ecosystems following
any disturbance. Succession is dependent
on the physiological, population, and
community ecology of the resident flora
and fauna, as well as site and disturbance
characteristics (Bazzaz 1996). A disturbance is a natural or anthropogenic event
that destroys biomass and alters ecosystem
structure and resource availability (Pickett
et al. 1987, Attiwill 1994). Forest fires,
insect outbreaks, windthrow, ice damage
and harvesting are examples of disturbances. The size, frequency, intensity and
seasonality of disturbances influence
successional pathways through effects on
resource availability and sources of vegetation (seed, seed bank, vegetative reproduction, advance reproduction) available for
the colonization of the new growing space
(Oliver 1980, Petersen and Carson 1996).
The Boreal and Great Lakes-St. Lawrence (GLSL) Forest Regions of Ontario
differ in their natural disturbance regimes.
Boreal forest ecosystem dynamics are
driven by disturbance such as wildfire and
insects. Large, stand replacing crown fires
at 70- to 100-year intervals were the primary natural disturbance in the Boreal
Forest Region of Ontario, and favoured the
establishment of forests dominated by
early successional, fire adapted jack pine,
black spruce and poplar (Johnson 1992).
Defoliating insects also play a major role in
boreal forests. Spruce budworm outbreaks
lasting 5 to 15 years occur at 40-year intervals, affect large areas and predispose
infested areas to wildfire 5 to 8 years after
stand mortality (Stocks 1987).
Catastrophic fire is less frequent in the
GLSL Forest Region. In drier portions of
the GLSL Region, crown fires occur at
comparatively longer intervals (ca. 150 to
250 yr.). Frequent (20 to 40 yr.), low intensity, surface fires reduce the numbers of
fire-sensitive, shade tolerant species, increase understory light levels, and favour
sub-climax forests dominated by white
pine, red pine and red oak (Heinselman
1973, Whitney 1986). In more mesic habitats of the GLSL Forest Region, forests are
dominated by late successional, tolerant
hardwood species and eastern hemlock, as
large scale disturbances by fire and catastrophic windstorms (e.g., tornadoes) are
rare, with a return interval >1200 years
(Canham and Loucks 1984, Whitney 1986).
Comparatively frequent, low intensity
wind storms (thunderstorms and periodic
high winds) are the primary natural disturbance in these forests, affect a small percentage (<1.0%) of a given area annually,
and form canopy gaps (100 to 400 m2)
through windthrow of single or small
groups of trees. Smaller canopy gaps form
after the death of single trees, with return
intervals of 120 to 190 years (Dahir and
Lorimer 1996). These small gaps favour
advance reproduction of shade tolerant
overstory species.
Climate change can be viewed as a
progressive, anthropogenic disturbance
with an unusually long time frame relative
to natural disturbances. Altered temperature and precipitation regimes and elevated CO2 will have a direct impact on
forest structure through their effects
on the physiology and population ecology
of plant species, as well as ecosystem
processes such as decomposition, nutrient
cycling, and plant interactions with other
organisms (see Sections 4, 5 and 7). However, the increased frequency of disturbances due to fire, insects and extreme
weather expected to accompany climate
change will likely exert a stronger effect on
forest vegetation than the effects of modified climate alone, by increasing the rate at
which an equilibrium between vegetation
and climate is attained (Davis and Botkin
1985, Overpeck et al. 1990, Bazzaz 1996).
In Ontario, regional differences in vegetation response to climate change will depend on the plant species present, site
quality, and relative change in the current
climatic and disturbance regimes (Davis
and Botkin 1985, Grime 1993).
Changes in temperature and precipitation associated with a doubling of atmospheric CO2 could increase the forest
area burned annually in Canada by almost
50% (Flannigan and van Wagner 1991,
Wotton and Flanningan 1993). In Ontario,
increased frequency of wildfire is predicted for the boreal forests in the northwest, and GLSL forests of the central and
southern regions of the province (see
Section 6). If the warmer climate results in
higher incidence of insect outbreaks, the
risk of fire could be further increased
(Fleming 1996). In the boreal forest region,
more frequent wildfires will increase the
number of young, early successional
ecosystems dominated by fire-adapted
shade intolerant species (Grime 1993,
Bazzaz 1996), while in northwest Ontario,
boreal forests may be replaced by
grasslands and aspen parklands (Hogg
and Hurdle 1995).
A preview of the potential consequences of climate change in the Boreal
Forest Region is illustrated in the Experimental Lakes Area in northwestern Ontario (Schindler 1998). The period 1970 to
1990 was abnormally warm and dry.
Several, large lightning-ignited forest fires
occurred, followed by revegetation of
burned areas by fire-adapted jack pine
and black spruce. Because of the hot, dry
growing seasons that followed, mortality
of conifer regeneration was high. Some of
these areas burned a second time, resulting in the replacement of conifers by
trembling aspen and balsam poplar, while
some sites remained barren of vegetation
17 years after the second fire.
In the GLSL Forest Region, the predicted 4 to 6oC increase in growing season
temperature with little change in precipitation (see Section 2) will increase disturbance by climatic stress events and fire
(see Section 6) (Overpeck et al. 1990).
Periodic drought may weaken forest
stands and initiate “growth decline”,
mortality and the formation of canopy
gaps (Millers et al. 1989, LeBlanc and
Foster 1992, Reed and Desanker 1992).
Overstory individuals suffering decline
will be vulnerable to secondary attack by
insects and diseases, further accelerating
stand senescence. Lower quality sites will
be affected first, as will species with narrow ecological amplitude (e.g., red pine,
hemlock) (Solomon 1986). Canopy gaps
will initiate release of the understory, the
species composition of which will depend
on climate and past management effects
on regeneration (Davis and Botkin 1985).
Increased frequency of surface fires, related in part to the higher fuel loading in
declining stands, could slow the current
successional displacement of fire-dependent white pine and red oak by fire-sensitive sugar maple and balsam fir.
Models predict dramatic changes in
forest composition and cover in Ontario
based on changes in temperature and
precipitation (Solomon 1986, Pastor and
Post 1988, Sargent 1988, Solomon and
Bartlein 1992, Lenihan and Neilson 1993,
Mackey and Sims 1993). These models
predict the Boreal Forest Region will move
northward, displaced by the northward
expansion of temperate conifer and hardwood species of the GLSL Forest Region
(maple, basswood, oak, white pine). However, these models likely overestimate the
impact of changing climate on forest vegetation dynamics, as they do not adequately account for the effects of CO2
enrichment, barriers to migration, competition, soil characteristics, physiological
tolerance and acclimation, genetic variation, disturbance regime, etc. (see Section
11) (Lenihan and Neilson 1993, Loehle and
LeBlanc 1996). More accurate model predictions must await a better understanding
of the long-term effects of the interaction
of climate change, CO2 and other environmental factors on forest ecosystem structure and function. Despite this current
uncertainty, more frequent wildfire and
forest decline will likely increase the area
occupied by early successional ecosystems
at the expense of mid- and late successional ecosystems. In the near term, techniques are needed to identify vulnerable,
declining stands requiring silvicultural
intervention to minimize potential effects
of climate change on Ontario’s forests.
Section 10.
The Use of Models in Global Climate Change
Studies
Michael T. Ter-Mikaelian, Ontario Forest
Research Institute, Ministry of Natural
Resources
Models are commonly used to predict
the effects of climate change on forest ecosystems. Models are popular because: (i)
predictions are necessary either for
situation(s) that have not yet occurred or for
which data are not available; (ii) forest
ecosystems develop and change over long
periods — studying the effects of potential
climate change would require decades,
which unfortunately also corresponds to the
desired prediction time; and (iii) forest
ecosystems are hierarchical multi-component systems — climate change may affect
these components differently both in terms
of direction and magnitude. Even if the
separate effects of climate change on each
component were known, their interactions
make assembling a complete description of
ecosystem effects difficult. Models provide
an indirect method of predicting attributes
of forest ecosystems and how they change
over time.
Unfortunately, there is no existing
model comprehensive enough to predict the
response of forest ecosystems in Ontario to
climate change. In order to save time and
resources, a model predicting climate
change effects on forests should be developed using existing blocks (or modules)
from other models. Table 10.1 presents
examples of potential modules for some key
areas of forest ecology and management.
The following criteria were used to select
these examples: (i) the model included
climatic variables that can be manipulated
to predict the effects of climate change on
the forest; (ii) the temporal resolution of
these variables should match the long-term
resolution of the climatic models generating
future climate scenarios (e.g., a model
requiring daily values of some meteorological variable was considered impractical);
(iii) preference was given to models that
deal with a single process. For comprehensive reviews of climate change-related
models the reader is referred to Goudriaan
et al. (1998), Loehle and LeBlanc (1996), and
Urban and Shugart (1992).
Some of the models in Table 11.1 can be
applied to climate change predictions for
Ontario immediately. Most of the models
can be used independently to describe a
specific process or assembled into a more
complex model addressing several processes simultaneously. In both situations,
there are several guidelines to follow when
modelling the effects of climate change on
forest ecosystems:
Spatial scale. Although many processes
operate at a number of scales, direct effects
can usually be associated with one particular scale. For example, wildfires operate at
tree—stand—landscape scales (they burn
individual trees and stands, and change
landscape structure); however, the effects
are most pronounced at the landscape scale.
Therefore, when simulating a process, one
has to identify the scale at which the effects
are most pronounced (target scale); other
relevant scales can be included if the model
is multi-scaled.
Spatial hierarchy. Some processes may
be adversely influenced by climate change
at scales other than the target scale. Consider the task of estimating the effects of air
temperature increases on forest productivity at the stand level. At the tree level,
increased temperature increases individual
tree biomass; at the stand level, it decreases
stand density since trees compete more
intensively as their size increases. Thus,
elevated temperature may either increase
or decrease productivity at the stand level;
the effect cannot be estimated without more
accurate quantification of both processes.
Similarly, if we were interested in effects at
the landscape level, we would have to account for the effect on productivity at the
stand level, as well as increased fire frequency which decreases the mean forest age.
Therefore, models should include effects at
the target scale and one step below the
target scale to ensure accuracy.
Temporal scale: Equilibrium state vs.
transition state. "Transition state” predictions are given for periods when the climate
is actually changing. Transition state models
account for transition processes (e.g., rates of
species migration to new geographic areas);
these models are time-specific, i.e., a time
can be specified for each prediction. “Equilibrium state” predictions assume that the
climate will change and then remain stable
for a period sufficient for ecological processes to come to an equilibrium. Equilibrium
models are simpler because they ignore
some of the processes considered in transition state models. Their predictions, however, are not time-specific since it is impossible to know when an equilibrium state is
reached. Thus, when building a model it is
necessary to decide which type of prediction
should be made. The majority of existing
models are equilibrium models.
Temporal scale: Short-term vs. long-term
predictions. If a transition state model is
chosen, the length of projection needs to be
specified. Rates of climate-induced change
will differ for different processes; therefore,
depending on the prediction time, some
processes may be considered ”stable” and
therefore omitted from the model, while
others have to be modelled. For example, for
a 5-year prediction it is reasonable to assume
that the current geographic distribution of
species will not change, while in a 50-year
prediction possible shifts in species zones
must be accounted for.
Temporal resolution. It is important to
select appropriate temporal resolution (time
steps) for modelling climate change effects.
Large time steps can inadequately represent
a process because (a) the mean of the proc-
ess may be roughly the same but the variation may change dramatically, and (b) some
sub-periods within a selected time step may
be more important than others. For example,
warmer winters may have unique effects
depending on tree species: (a) evergreen
species will be affected by increased
evapotranspiration more than deciduous
species, (b) warmer winters and earlier
springs may adversely influence some tree
species if they interfere with chilling requirements for bud break phenology. At present,
time steps should not be shorter than a
month, because climatic models are not
accurate at shorter intervals.
Climatic variables. It is important to
identify the variables affecting the target
ecological process. Most climate change
predictions are given in terms of increasing
air temperature, which does not necessarily
translate into a change of the same magnitude for some ecological variables. For example, Street (1989) demonstrated how trends in
two variables (temperature and precipitation) compensate for each other’s effect on
forest fires, resulting in more moderate
predictions than those based on a single
variable trend.
There will be few chances to validate a
“climate change” model in the traditional
sense. For this reason, indirect testing of the
accuracy of climate change models will be
needed. Such testing can be done by independently testing modules of the larger
model. One means of testing the accuracy of
a climate change model is to determine
whether the model is able to predict past
effects of climate on vegetation or ecological
processes. Another way to test a climate
change model is to evaluate the survival and
growth of species planted outside their
native ranges (Loehle and Leblanc 1996). In
this context, process models (i.e., those based
on measurable ecological processes that are
causally related to climate) may have advantages over statistical models (i.e., models
based on correlations between climate and an
ecological process that may not have a causal
relationship) for indirect testing of the accuracy of climate change models (see
Korzukhin et al. 1996).
Model title/
reference
Arp and Yin 1992
CLIMEX/
Sutherst et al.
1995
Gross 1985
ForLand/
Antonovski et
al. 1992
Field
Hydrology
Insects
Disease
Fire
To predict the effects
of climate on longterm forest fire
dynamics
To identify white pine
blister rust
(Cronartium ribicola
J.C. Fisch.) hazard
zones
To simulate geographic
distribution of insects
using climatic variables
and species phenology
To predict major water
fluxes through upland
forests from commonly
available monthly
climate records and
descriptive site
information
Objective
Landscape/
1 year
Large-scale
(province)/
static
Large-scale
(continent)/
static1
Watershed/
about 1 day
Spatial scale/
time step
Seasonal mean
temperature;
seasonal
precipitation;
maximum drought
period
Mean minimum
July temperature;
mean daily July
temperature;
mean annual frostfree period; mean
date of first frost
Weekly mean
temperature;
weekly
precipitation
Monthly mean
temperature;
monthly
precipitation;
monthly mean
snow fraction of
precipitation
Input climatic
variables
Calibrated for 1600
km2 softwooddominated
landscape in
western Siberia
Has been used to
identify 4 hazard
zones (low,
intermediate, high,
and severe) for
Ontario
Has been applied to
predict the distribution
of Colorado beetle in
North America, and
livestock tick in Europe
Calibrated and tested
for 2 watersheds
(4.62 and 62.3 ha)
near Turkey Lakes;
Ontario
Application
Table 10.1 A list of models and their characteristics that can be readily adapted for studying climate change effects in Ontario.
Calibration for Ontario would
require estimation of key
model parameters
Needs further analytical
development; see also
Brasier (1996) for an
application of CLIMEX to
predict geographic
distribution of Phytophthora
cinnamomi (tree root pathogen)
Requires calibration for
Ontario. Since the model
assumes that geographic
distribution of a species
is defined primarily
by climate, it may be
applicable to certain species
(e.g., Gypsy moth)
No modification
required
Comments
To predict general
yield classes from
long-term climatic
factors
ForClim/
Bugmann 1996
Kellomaki et al.
1992
Proe et al.
1996;
Tyler et al.
1995
Plant
succession
Growth and
yield
1
To simulate growth
and yield of tree
stands from
physiological principles
Carter 1996;
Schmidtling
1994
Genetics
Stand/
1 year
1/12 ha/
1 year
1/12 ha/
1 year
Plantation/
static (predicts
the height at
ages 8-22 years
depending on
species)
Stand (assumes
spatial
homogeneity
of soil)/
1 month
Spatial scale/
time step
Monthly mean
temperature;
monthly
precipitation
Monthly mean
temperature;
monthly
precipitation
Monthly mean
temperature;
monthly
precipitation
Annual mean
minimum
temperature
Monthly mean daytime VPD; monthly
precipitation; mean
number of frost-free
days per month
Input climatic
variables
Douglas-fir and Sitka
spruce in Scotland
Tested against growth
and yield tables for
Scots pine, Norway
spruce, and birch
spp. in Finland
Tested for a large
number of sites in the
European Alps and
North America
Applied to 12
softwood and
hardwood species
(e.g., balsam fir,
eastern white pine,
jack pine, white
spruce, etc.)
Has been tested as
growth and yield
simulator of radiata
pine in Australia and
New Zealand
Application
a model where the output is for an "equilibrium" condition has no time step and is therefore "static", since it predicts only a single "state"
To simulate the effects
of climate on forest
structure, composition
and dynamics
To predict the effects
of temperature change
on tree height growth
from multi-location
provenance trial data
To simulate the growth
and yield of a forest
stand from simple
physiological principles
3-PG/
Landsberg and
Waring 1997
Tree
physiology
Objective
Model title/
reference
Field
Table 10.1 Continued
Calibration for Ontario would
require large, spatially
distributed data sets on
long-term productivity of
forests
Requires calibration for
Ontario; see also Landsberg
and Waring 1997
Requires calibration for
Ontario; see also Kellomaki
et al. (1992)
No modification required;
further studies needed to
estimate response after
the prediction date
An individual-tree growth
module should be extracted
and calibrated for Ontario
species; see also Kellomaki
et al. (1992) for a module
simulating frost damage
Comments
Section 11.
Forest Management Responses to Climate
Change
William C. Parker, Stephen J. Colombo, Marilyn L.
Cherry, Sylvia Greifenhagen, Chris S. Papadopol,
and Taylor Scarr, Ministry of Natural Resources
If the forecast changes in climate due
to increasing atmospheric CO2 are realized,
forests established now will mature in an
environment that is substantially different
from today. This report considers possible
climate effects on Ontario’s forests based
on projections from published literature
and our interpretations of likely effects in
Ontario. The question that naturally follows from this consideration of climate
effects is what, if anything, can be done to
minimize negative consequences to our
forests arising from climate change.
Forest management is the practice of
silviculture to direct forest succession in a
way that a desired combination of forest
benefits is obtained, be it for timber, wilderness areas, wildlife habitat, old-growth
forests, or other valued products. Despite
uncertainties as to specific impacts, climate
change is likely to significantly alter forest
ecosystems and their management. Current socioeconomic trends emphasizing
non-commodity values of forests will
likely expand if forests begin to be managed as sinks for atmospheric CO2, for
their ability to modify climate, and as
reservoirs of biodiversity (Woodman
1990). As a result, traditional silviculture
may become increasingly less effective at
meeting future forest management objectives.
Table 11.1 lists some possible approaches to forest management in a changing climate. The timely development and
selective, appropriate use of innovative
approaches to forest management in response to climate change are imperative
given the inherently long planning scale of
forestry and the economic importance of
forests to Ontario. In this section we describe some potential silvicultural activities
that forest managers may use to reduce
negative impacts of climate change. We
also address the possible use of forests and
tree plantations to store CO2 and slow the
rate of climate change.
Silvicultural Systems and Stand Management
Disequilibrium between forest vegetation and climate will occur where rotation
length exceeds the development of a new
climatic regime. This disequilibrium will
be associated with regional episodes of
forest decline as overstory species are no
longer adapted to the prevailing climate
(see Section 9). This will require
silvicultural systems that address the
management and regeneration of declining
stands. Harvesting is the most effective
tool available to forest managers for altering forest condition and may be used to
maintain forest health and productivity.
For example, in younger stands not ready
for commercial harvest, stand productivity
and health may be maintained or improved by thinning to remove suppressed,
damaged or poor quality individuals,
increase the vigour of selected overstory
individuals, and reduce the likelihood of
decline (Table 11.1). Alternatively, in older
stands productivity has declined as a result
of overstory species being poorly adapted
to the new climate, logging and planting
prior to stand deterioration may be used to
Purpose
Harvest chronically stressed stands of low vigour and slower growth rates that are susceptible to insects and disease
Reduce insect and disease susceptibility, and increase vigour through thinning, when stands are under prolonged and
severe moisture stress
Regenerate drought prone habitats with deeply-rooted species; select and breed drought tolerant genotypes
Protect regeneration from future warmer, drier seedling environments. Increase the amount of carbon stored by increasing
the period a site is occupied by trees, decreasing disturbance to forest floor, and increasing the rate of reforestation where
advance reproduction is used
Greater incidence of extreme events and drought are expected to increase tree stress and susceptibility to insect pests
Introduce southern species beyond recent northern range limits when temperature averages and extremes have warmed
sufficiently
Protecting diversity increases the likelihood that there will be individuals, species, and ecosystems that are adapted to
future climate conditions; requires strategies for genetic conservation and ecosystem protection
Increasing the amount of carbon stored by increasing the period a site is occupied by trees
Periodic updating of seed zones based on temperature averages and extremes
Longer growing seasons, warmer temperatures and reduced precipitation may already have increased forest fire activity.
Protection of valued forests requires a compensatory increase in forest fire suppression
Increasing the amount of carbon stored by increasing the area covered by forests
Increasing the amount of carbon sequestered by increasing the length of time it is sequestered (e.g., in order of increasing
sequestration time: non-recyclable paper; recyclable paper; books; lumber and construction board)
Advance reproduction requires less energy input compared to artificial regeneration and increases the rate of reforestation;
need to develop and use modified harvesting techniques to protect reproduction and residual overstory when logging
Activity
Shorten rotation lengths, where
appropriate
Thinning
Plant drought-adapted species
and genotypes
Increase use of alternatives to
clearcutting (e.g., shelterwood,
selection systems)
Increase insect pest
management preparedness
Plant climate-adapted species
Maintain genetic and biological
diversity
Rapidly reestablish trees in
harvested forests
Use climate-based seed zones
Increase forest fire suppression
Afforest non-forested land
Preferentially regenerate trees
for use in long-lived wood
products
Increase use of advance
reproduction
Table 11.1. Potential forest management activities to minimize the negative effects of climate change on Ontario’s forests. The suitability of these activities will
vary with the extent of climatic change, the condition of the stand in question, management objectives, and forest policy.
speed the replacement of forest types
(Table 11.1). Techniques for monitoring the
health of existing stands will be critical to
the timely identification of areas needing
protection or silvicultural intervention.
Harvesting can serve the dual purpose of facilitating the regeneration of the
next stand if applied to protect or promote
the advance reproduction of more siteadapted species in the understory, if they
occur. Where the understory is not properly matched to the prevailing site or
climate conditions, and not acceptable as a
source of regeneration, planting will be
required. As artificial regeneration is
vulnerable to environmental stresses
following planting, partial cutting systems
can be used to moderate the warmer, drier
seedling environment predicted for the
future (see Section 2). Partial cutting and
thinning need to be tailored to the ecology
of the species desired for regeneration
(Hedden 1989, Ostofsky 1989). However, if
climate change alters basic elements of
forest ecology, the species or populations
desired and the practices required for
regeneration success may change in as yet
unpredictable ways.
As many insect pests and forest diseases are stress-related, “stress management” practices such as partial cutting or
thinning may also be useful to reduce
susceptibility to insects and diseases
(Wargo and Harrington 1991). However, as
these same practices can sometimes increase vulnerability to other insects and
diseases (e.g., jack pine budworm,
Hypoxylon canker of aspen, and
Armillaria in conifers), site and species
specific application will be needed. Shortening the rotation length can be used to
decrease the period of vulnerability to
stress. Other silvicultural techniques that
reduce stress and susceptibility to insects
and diseases include the regulation of
species composition (i.e., planting appropriate species on sites) and maintainance
of biological diversity.
Climate change will affect the life
cycle of forest pathogens, and therefore,
the amount of damage suffered due to
insects and diseases (see Sections 4 and 5).
Gypsy moth, a significant defoliating
insect in southern Ontario, could increase
in severity if the incidence of fall drought
and warm spring temperatures is favoured
by climate change (Wagner 1990). In contrast, warm weather in the spring and fall
could adversely affect spruce budworm,
reducing tree losses to this insect
(Safranyik 1990). Shifts in the geographic
range of insects may result in the introduction of new species to Ontario. According
to Safranyik (1990), the mountain pine
beetle, presently found in South Dakota,
could migrate northward if winter minimum temperatures warm. This serious
forest insect pest could cause losses to pine
forests in northwestern Ontario. Were
climate change to result in periods of
severe insect infestation, insecticides might
be needed to protect young stands and
reduce losses in timber volume and forest
cover (Table 11.1).
Forest Regeneration
If the 3 to 4o C increase in annual
average temperature predicted for the next
50 years occurs, species will have to migrate approximately 300 km to the north
over that time to be matched to climate.
However, the migration rates of forest tree
species are too slow to keep pace with this
magnitude of climate change (Roberts
1989). Human-caused landscape fragmentation (e.g., agricultural lands, urbanization), lack of suitable habitat, and natural
barriers to plant migration (e.g., the Great
Lakes) will also hinder the movement of
species from their current to potential
future ranges.
Forest management provides an
avenue to assist the movement of species
from current to future ranges, but major
artificial regeneration efforts will be required to accomplish this (Davis 1989,
Mackey and Sims 1993). Experimental
planting of selected species and
populations to appropriate sites up to 100
km north of their current range could be
used to test the ability to assist species
migration. Provenance trials that test
populations from a wide variety of sites
located across the range of a species will
contribute to this effort by providing information about the transferability of species
and populations to new environments.
Species and population transfer northward
needs to also account for photoperiod
adaptation, since day length affects the
onset and cessation of growth. It has been
suggested that reserve areas, such as parks,
be linked through connective corridors in a
north-south gradient to aid species migration (Halpin 1997). However, northward
movement of species in Ontario is complicated by the lack of suitable soil types and
the expected lag in soil development during climate change. The movement of more
nutrient demanding hardwoods to acidic,
less fertile sites now occupied by conifers
may benefit from mixed planting with
species that ameliorate site conditions (e.g.,
N-fixers). This may also require planting
hardwood species inoculated with siteadapted mycorrhizal species. Habitats
expected to become drier in the future
might be regenerated with novel, more
deeply rooted species (Table 11.1).
The amount of silvicultural intervention needed to maintain a productive forest
will depend on the forest species in question, but it is clear that an effective genetic
resource management program will be an
important component of forest management response to climate change. Widely
distributed species (e.g., black spruce and
white spruce), which have broad genetic
diversity, may require little attention, but
local ecotypes may be lost and genetic
diversity reduced. Maintaining species
currently of economic importance but with
greatly diminished natural abundance due
to past management practices (e.g., white
pine, red pine and red oak) may require the
identification, production, and planting of
southern ecotypes adapted to the longer
photoperiods of more northern regions.
Assessing genetic variation within these
species will help to determine the limits of
transferability along climatic gradients and,
perhaps, will require periodic adjustment
of existing climate-based seed zones (Table
11.1). Given the current uncertainty regarding regional shifts in climate, planting stock
representing widely adapted populations
and diverse seed source mixtures can be
used to increase the likelihood of regeneration success. Aggressive genetic tree improvement programs designed to promote
increased genetic diversity and allow for
future adaptation will also be needed to
increase pest resistance and tolerance to
environmental stresses (Roberts 1989)
(Table 11.1).
Climate change may threaten rare
species because they lack enough economic
value to warrant addressing the potential
loss of suitable habitat (Peters 1990).
Butternut, red mulberry, and red spruce are
a few of the comparatively rare tree species
in Ontario that are confined to small, disjunct populations. These and similarly rare
species may require more intensive, costly
silvicultural activities to sustain them if
suitable habitat becomes difficult to find or
create due to climate change. As a consequence, conservation plans and
silvicultural approaches to sustain rare,
threatened and endangered species are
needed. Increasing the number of large
natural areas or reserves to maintain a wide
variety of habitat conditions has been
recommended to reduce the risk of local
extinction of rare species (Peters 1990), but
this by itself may be insufficient to prevent
extinction. Breeding plans for rare species
that incorporate systems to increase genetic
diversity should be used. However, our
ability to only forestall rather than prevent
local extinction needs to be weighed against
the cost of preservation activities. In addition, severe habitat loss could mean that
long-term preservation of rare species may
only be possible in “zoo-like” arboreta,
rather than in natural environments.
More intensive vegetation management
treatments to control less desirable tree
species and other plants may, in the future,
be required to assist the regeneration of
preferred commercial forestry species. This
may occur because of the comparatively
pronounced growth response of some
plants to elevated CO2 and warmer temperatures. Hardwoods show a greater
proportional increase in biomass under
elevated CO2 and may increase in competitive fitness relative to conifer species
(McGuire et al. 1995). Further, fast growing, short-lived herbaceous species are
better able to adapt genetically to increased
atmospheric CO2. As a result, a general
increase in the abundance of aggressive
herbaceous plants may occur, particularly
where stand senescence exceeds the rate of
ingress of more adapted tree species
(Bazzaz 1996). Poplar and aspen species are
likely to become more aggressive in boreal
regions, as their high relative growth rates
and reproduction from root suckers favour
their colonization after clearcutting and
wildfire. It is predicted that such changes in
the competitive interaction among tree
species could result in the development of
plant communities for which we have no
management experience, requiring new
silvicultural approaches to control non-crop
species (Davis 1989, Bazzaz 1996).
Mycorrhizal associations with plants
are important to forest regeneration efforts
because they help reduce plant stress by
improving the absorption of nutrients and
soil moisture. Practices such as clearcutting,
whole-tree harvesting and prescribed burning can decrease the diversity and total
biomass of mycorrhizae and may potentially increase adverse effects where climate
change increases the severity and frequency
of drought (Harvey et al. 1980, Miller and
Lodge 1997). Harvey et al. (1980) recommend keeping clearcuts small and maximizing edges to promote the ingress of
mycorrhizae from surrounding uncut
stands. Such practices help maintain the
diversity of soil microorganisms, which
increases the ability of ecosystems to adapt
to a range of climatic conditions. Mixed
plantings of conifers and hardwoods can
increase microbial diversity and enhance
litter decay (Hendrickson et al. 1982), as can
harvest and site preparation techniques that
promote litter accumulation or retention.
Fire frequency is expected to increase in
many areas of Ontario and, although certain mycorrhizal communities may be more
abundant after a fire, they may not be
suited to the desired tree and plant species
(see Section 5). In such instances, novel
approaches to maintaining fungal diversity
may be needed.
Biodiversity has been defined as “the
variability among living organisms and the
ecological complexes of which they are a
part” (Canadian Council of Forest Ministers
1997). It can be viewed in the context of the
biodiversity of ecosystems, species and
genes (Canadian Council of Forest Ministers 1997). The conservation of biodiversity
is an important goal of sustainable forest
management. However, should a change in
climate alter a crucial aspect of the environment, then, regardless of forest management activities, biodiversity will change.
One way to retain biodiversity is to protect
old-growth forests and other natural areas,
as these habitats serve as biodiversity
reservoirs (while also acting as forest carbon storage areas, as described later). However, the ability to retain such areas is likely
to decline if climate changes rapidly and
the frequency and severity of forest disturbance increases. A more dynamic approach
recognizing that conditions may change is
needed to protect natural areas through a
period of climate change (Halpin 1997)
Forest Productivity
The influence of climate change on
forest productivity will depend on regional
differences in effects of elevated CO2 concentration and altered climatic regimes on
carbon, water and nutrient relations, environmental stress response, and the unique
ecophysiological characteristics of species
(Bazzaz et al. 1990, McGuire et al. 1995,
Wayne et al. 1998). Although enhanced
photosynthetic activity at elevated CO2
concentrations will increase forest net
primary productivity (NPP), the relative
increase in photosynthesis is strongly
dependent upon nitrogen availability
(Melillo et al. 1993, McGuire et al. 1995).
For example, the potential increase in NPP
of northern and temperate forest ecosystems under elevated CO2 may be constrained by nitrogen availability in soils of
these regions, with NPP being largely
dependent on effects of elevated temperature on mineralization rates (Melillo et al.
1993). Further, the beneficial effects of CO2
fertilization on NPP expected under climate change may decline with time (Cao
and Woodward 1998).
Rigorous predictions of climate
change effects on NPP must await further
progress in our understanding of the
relationship between carbon and nitrogen
cycles (McGuire et al. 1995). However,
general statements regarding the possible
effects of climate change on forest productivity can be made. As shown in Table 11.2,
stand productivity will tend to increase in
all regions as a result of increased temperature and atmospheric CO2 concentration. Increased spring and fall temperatures will tend to lengthen the growing
season, while elevated CO2 will increase
photosynthesis and water use efficiency
(see Section 7). Nitrogen availability in
soils would tend to increase with temperature as a result of increased rates of mineralization and decomposition (see Sections
5 and 9), although the effect could be
relatively less in the south due to the
warmer temperatures that already prevail
there. However, reduced precipitation and
increasing severity of drought in the northwest and south could counter the positive
effects of warmer temperature, increased
CO2, and greater nitrogen availability. In
contrast, there could be large increases in
stand productivity in the northeast if
precipitation increases and the incidence
of drought decreases as predicted (see
Sections 2 and 3). Perennial herbaceous
plant competition (e.g., fireweed and
strawberry) may become a more serious
problem that would slow crop tree establishment, since herbaceous plants are
favoured under higher concentrations of
atmospheric CO2 (see Sections 7 and 9).
On a regional basis, an increased
incidence of severe disturbance could have
serious consequences on timber supply. In
northwestern Ontario, reduced precipitation could trigger severe pest outbreaks
(see Sections 4 and 5) and forest fires (see
Section 6). Similar effects, although perhaps less severe, may also occur in southern Ontario. Despite predicted increases in
precipitation in the northeast, there may be
an increase in fire severity due to drying
caused by elevated temperatures and high
evaporative demands (see Sections 3 and
6).
Carbon Sequestration
The total global carbon content is
constant; it occurs as atmospheric CO2 and
oceanic carbon or in storage as living and
dead biomass, fossil fuels, limestone, and
marble. Atmospheric CO2 concentration
depends on the balance between carbon
“fixed”, or added, in storage and released
from storage. Since the beginning of the
industrial era, atmospheric CO2 concentration has increased from about 280 ppm to
360 ppm. Approximately 7 Gt CO2-carbon
per year (Gt=gigaton; 1 Gt=1015 g) are
being released to the atmosphere by fossil
fuel combustion and, to a much lesser
extent, tropical deforestation and burning
(Krauchi 1994). Of this carbon, 3.6 Gt are
absorbed by oceans and terrestrial vegetation, with 3.4 Gt being added annually to
the atmosphere.
Forests play an integral role in the
global carbon cycle, fixing CO2 through
photosynthesis, storing carbon in above
and below ground biomass, and releasing
CO2 to the atmosphere through decomposition and respiration (D’Arrigo et al. 1987,
Tans et al. 1990, Krauchi 1994). Forest
biomass contains about 70% of the amount
of carbon in the atmosphere, while carbon
in detritus and soil organic matter is twice
that of the atmosphere. Natural and
anthropogenic disturbances influence the
carbon cycle of forest ecosystems through
effects on the amount of carbon stored and
its rate of transfer from organic storage
forms to the atmosphere. Generally, a reduction in rotation length and shorter natural
disturbance intervals reduce carbon storage
(Cooper 1983). The carbon storage life of
forest products also influences the forest
carbon cycle. Currently, harvesting and
industrial processing of boreal and temperate forests results in two-thirds of the stored
carbon being emitted to the atmosphere as
CO2 (Harmon et al. 1990, Freedman and
Keith 1996).
Atmospheric CO2 concentrations can
be reduced by decreasing fossil fuel combustion and increasing the rate of carbon
removal from the atmosphere. For a variety
of reasons, significant reductions in fossil
fuel emissions are unlikely in the near
future (Freedman and Keith 1996). Forestry
is one of the few human activities that can
reduce atmospheric CO2. Using forests as
sinks to reduce net CO2 emissions is a promising way to mitigate climate change, but
should be used in conjunction with efforts to
reduce fossil fuel combustion and deforestation (Sedjo 1989, Freedman and Keith 1996).
Managing forests as carbon sinks would
require some changes in the forest land use
paradigm to add the maximization of carbon storage and afforestation to the goals of
rapid reforestation and increased productivity.
Afforestation for carbon storage by
establishing tree plantations on marginal
cropland and pasture can be used as an
effective, ecologically viable means of increasing CO2 sequestration (Winjum and
Schroeder 1997). However, in Ontario the
amount of land available for afforestation is
small compared to the existing forested land
base. The potential reduction in CO2 by
afforestation depends on availability of
lands that can grow forests, the maximum
attainable biomass of these forests,
Table 11.2 Possible effects of altered environment induced by climate change on forest productivity and timber supply in
northwestern, northeastern and south central Ontario in the next 50 to 100 years1.
Processes and Factors
Northwest
Northeast
South central
+
+
+
+
+
+
+
+
0
--
+
+
-
-
--
-
Fire disturbance
--
-
--
Insect
--
0
-
Disease
--
0
-
Net effects on stand productivity
--
+
+
0
-
Environment:
elevated temperature
increased CO2 concentration
nitrogen availability
Hydrology:
precipitation
drought
Increased herbaceous competition
Net effects on regional timber supply
1
a preliminary version of this table was prepared by Changhui Peng, OFRI.
the degree to which management alters this
maximum, and the long-term fate of stored
carbon (Table 11.1) (Cooper 1983, Vitousek
1991, Winjum and Schroeder 1997). Large
monoculture tree plantations are more
susceptible to insects and pathogens
(Winjum and Schroeder 1997), and their
use to maximize carbon storage requires
that they be protected from fire and insects.
A total of 61 million ha, or 62%, of
Ontario’s total land area is productive
forested land (OMNR 1996). Forest management can increase the productivity and
carbon storage of these existing forests, but
the contribution to carbon sequestration on
a per hectare basis would be less than the
contribution from afforestation of nonforested land. Other broad management
practices recommended to maximize carbon sequestration of forest land include: (i)
clearing and prompt regeneration of unproductive, poorly stocked forest, (ii) intermediate stand treatments (e.g., thinning) in
overstocked, stagnating forests, and (iii)
increasing the rotation length (Birdsey and
Heath 1997).
The net amount of carbon stored in
forest ecosystems will differ with the
silvicultural system used (Figure 11.1). A
clearcut silvicultural system has the greatest CO2 output from fossil fuels per unit
rotation while a selection system produces
the smallest CO2 output. Clearcutting
followed by tree planting produces a large
release of CO2 from fossil fuels because of
the energy requirements for tree seedling
production, transportation, site preparation and tending, and from accelerated
decomposition of forest floor detritus and
organic matter after harvest. Selection
silviculture requires CO2 output for harvesting only, disturbance to the forest floor
is minimized, and planting is not required,
but these gains are partially offset by the
need for a larger road network, greater
frequency of return to harvest, and lower
efficiency (i.e., lower m3 of wood per
hectare of forest).
Figure 11.1 Theoretical contributions of some silvicultural activities to the net sequestration of carbon by trees.
Estimates of net carbon sequestration must account for both the effect on net carbon sequestration in stem
wood over the rotation of the stand and the release of CO2 by burning fossil fuels to carry out the activity.
Values shown are possible relative differences; actual levels may differ.
Figure 11.2 shows theoretical differences in net carbon sequestration with
different silvicultural practices. Not all
forms of silviculture will result in increased net sequestration of carbon. For
example, tree improvement is a
silvicultural practice that requires relatively small release of CO2 to achieve
increased growth rates over large areas of
forest. Vegetation management activities
reduce the interval between harvesting
and full site occupancy with a tree crop,
but the burning of fossil fuels and therefore CO2 released in producing, transporting and applying herbicide reduces the net
benefit of this practice to carbon sequestration. Pruning does not add to net sequestration of carbon and increases short-term
carbon release due to increased branch
decomposition rates, while adding little to
stand growth. Thinning increases individual tree vigour and concentrates
growth on fewer stems but, because it
requires an expenditure of energy to
Theoretical Co2 release and sequestration
at the end of a commercial rotation
Partial cutting systems (e.g., shelterwoods
and strip cuts) are intermediate in terms
of carbon sequestration, as they rely
heavily on seeding and advance growth
for regeneration, but may require planting
and some site preparation where natural
regeneration is inadequate. Moreover,
carbon sequestration decreases with the
length of time a forest site is not fully
occupied with a tree crop. Despite suggestions to the contrary, conversion of oldgrowth forest ecosystems to intensively
managed, commercial forests results in a
significant net decrease in on-site carbon
storage capacity (Harmon et al. 1990,
Vitousek 1991, Freedman and Keith 1996).
The value of old-growth forests as vehicles for carbon storage and preservation
of biodiversity may require development
of silvicultural approaches to maintain the
health of these forests under a changing
climate.
Figure 11.2 Theoretical release and sequestration of carbon using three silvicultural systems. Values shown
are possible relative release and sequestration levels; actual levels may differ.
conduct thinning mechanically and also
reduces full site occupancy, thinning reduces CO2 sequestration (thinning may
contribute positively to CO2 sequestration
if it reduces stand stress due to drought,
insects or disease). Finally, increases in
growth due to forest fertilization would be
offset by the large amount of CO2 emitted
in producing and applying fertilizer.
The consequences of management
practices on the forest carbon cycle will be
of increasing concern, particularly if minimizing net CO2 emissions becomes an
important objective of forest managers and
the forest industry. Such net calculations,
to our knowledge, have not yet been
widely made.
Conclusions
It is clear that the increase in greenhouse gases in the atmosphere over the last
two centuries is due to human activities
(Vitousek 1993). Despite current uncertainty as to the absolute effects of these
gases on the earth’s climate and biota,
there is compelling evidence to support
assertions that global climate change is a
serious threat to the biosphere. A significant warming of the earth’s atmosphere is
currently occurring, with the period since
1980 being the warmest in the past 200
years (Jacoby et al. 1996, Myneni et al.
1997, Mann et al. 1998). In fact, global
average temperatures for January to May
1998 indicate the spring of 1998 was the
warmest in the last 1000 years (Vogel and
Lawler 1998).
The warmer than normal temperatures in recent years may be responsible
for increased plant growth in the northern
latitudes, due to earlier disappearance of
snow in the spring and lengthening of the
growing season (Jacoby et al. 1996, Myneni
et al. 1997). However, in addition to, and
more important than, changes in temperature averages, climate change is expected
to increase the likelihood of extreme climatic events and associated natural disturbances (fire, insects), which will have
dramatic impacts on forest ecosystems.
Although it is difficult to state unequivocally that the warming already observed is
a direct result of increased greenhouse
gases, recent climate patterns and increased frequency of wildfire have already
had major effects on Ontario’s forests (Van
Wagner 1988, Schindler 1998).
Regardless of some continuing disagreement over the extent of the effect of
greenhouses gases on future global temperature, the increase in atmospheric CO2
will by itself be sufficient to substantially
alter forest ecosystems in Ontario. Some
effects of climate change and increased
atmospheric CO2 will be insidious and
progressive. For example, changes in the
competitive ability of different plants may
already be undergoing changes in a slow,
progressive manner. However, such
changes might not be apparent without
careful monitoring of plant species abundance and growth rates. Other ecosystem
changes, such as long-range species migration, might not be observed for hundreds
of years. Because of the uncertainty over
the timing and extent of climate change
and its effects on forest ecosystems, we
propose that “no risk” forest management
practices (i.e., practices that increase the
resilience of forests to climate variability,
such as the protection of genetic diversity)
be identified now and, where feasible,
implemented to minimize the potential
negative impacts of climate change and
increased atmospheric CO2 on forests in
Ontario. More dramatic responses to
climate change (e.g., the large-scale planting of southerly genetic sources and species hundreds of kilometers north of their
present ranges) should be considered once
improved regional climate change projections are made.
Section 12.
Conclusions
The Ontario Ministry of Natural
Resources seeks to sustain the ecological
and social benefits of healthy ecosystems
on forested Crown lands. However, forests
are increasingly being affected by acidification and deposition of nitrogen to soils
as a by-product of industrial pollution,
ground-level ozone pollution, and the
reduction of ozone in the earth’s upper
atmosphere that has increased ultraviolet
radiation. Overlain on these factors is a
potentially unprecedented rapid change in
climate resulting from increased atmospheric CO2. This report outlines the potential effects of CO2-induced climate change
on the stability of Ontario’s forest ecosystems.
The evidence reviewed in this report
identifies the following major effects of
climate change on Ontario’s forests:
• in northwestern Ontario, fires and
droughts will become more frequent and
severe;
• insect outbreaks and disease are expected to mirror fire and drought incidence;
• new plant associations are expected to
occur as individual species are favoured
over others and as rates of migration
differ between plant species;
• northeastern Ontario may experience
enhanced forest growth and productivity, while drought, fire, insects, and
disease in northwestern Ontario are
expected to reduce growth rates and
threaten wood supplies, perhaps within
the next 30 years;
• unique ecosystems and threatened and
endangered species may be unsustainable
if they have highly specific climate requirements;
• biodiversity conservation may change
meaning as a management objective if
climate change allows species to migrate
to new areas, there is strong genetic selection pressure, and the ability to reproduce
is reduced in some species.
The potential changes in climate described here would alter the traditional
economic and social benefits that society in
Ontario is accustomed to receiving from its
forests. It is therefore important that forest
land managers realize that existing forest
ecosystems and traditional approaches to
managing these lands may not be valid in a
climatically altered environment. As a
result, dynamic management practices and
policies governing forests in Ontario will be
needed in anticipation of such changes.
Careful sensitivity analysis to identify
species and ecosystems at greatest risk from
climate change is also needed. Optimizing
future forest management practices requires an understanding of the potential
consequences of climate change that can
only be obtained by modeling climatic
influences on biological systems.
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McFarlane, N.A., G.J. Boer, J.-P. Blanchet and M. Lazare. 1992.
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Weber, M.G. and M.D. Flannigan. 1997. Canadian boreal
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SECTION 3. FOREST HYDROLOGY IN RELATION
TO GLOBAL CHANGE
Bolin, B., B.R. Doos, J. Jagger and R.A. Warrick (eds.).
1986. The Greenhouse Effect, Climate Change, and
Ecosystems. John Wiley and Sons, Toronto, ON.
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Trans. Am. Geogr. Union, 27(1): 41-48.
SECTION 4. INSECTS AND CLIMATE CHANGE
Fleming, R.A. 1996. A mechanistic perspective of
possible influences of climate change on defoliating insects
in North America’s boreal forests. Silv. Fenn. 30: 281-294.
Fleming, R.A. and J.-N. Candau. 1997. Influences of climate
change on some ecological processes of an insect outbreak
system in Canada’s boreal forests and the implications for
biodiversity. Environ. Monit. Assess. 49: 235-249.
Fleming, R.A. and G.M. Tatchell. 1995. Shifts in flight periods
of British aphids: A response to climate warming? Pp. 505508 in R. Harrington and N. E. Stork (eds.), Insects in
Changing Environment. Academic Press, London, U.K.
Fleming, R.A. and W.J.A.Volney. 1995. Effects of climate
change on insect defoliator population processes in
Canada’s boreal forest: some plausible scenarios. Water,
Air, Soil Poll. 82: 445-454.
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spruce budworm defoliation in eastern North America,
1938-1980. USDA For. Serv., Co-op. Stat. Res. Serv. Misc.
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Hedden, R.L. 1988. Global climate change: Implications for
silviculture and pest management. Pp. 555-562 in Proc.
Fifth Biennal Southern Silvicultural Research Conference.
Memphis, Tennessee, Nov. 1-3, 1988. USDA For. Serv.,
South. For. Exp. Sta., Gen. Tech. Rep. SO-74.
Logan, J.A., P.V. Bolstad, B.J.Bentz and D.L. Perkins. 1995.
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Monz, C.A., H.W. Hunt, F.B. Reeves and E.T. Elliot. 1994. The
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Pflanzenschutz 37: 237-270.
Ojima, D.S., T.G.F. Kittal, T. Rosswall and B.H. Walker. 1991.
Critical issues for understanding global change effects on
terrestrial ecosystems. Ecol. Appl. 1: 316-325.
SECTION 5. THE IMPACT OF CLIMATE CHANGE ON
FUNGI IN THE FOREST ECOSYSTEM
O’Neill, E.G. 1994. Responses of soil biota to elevated
atmospheric carbon dioxide. Plant and Soil 65: 55-65.
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mycorrhiza and soil temperatures in relation to birch
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of climatic warming on trees and forests in the United
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Lodge, D.J., W.H. McDowell and C.P. McSwiney. 1994. The
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McDonald, G.I., N.E. Martin, and A.E. Harvey. 1987.
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susceptibility on pristine and disturbed sites. USDA For.
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SECTION 6. THE IMPACT OF CLIMATE CHANGE ON
FIRE AND FIRE MANAGEMENT IN ONTARIO
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of soil disturbance on growth and ectomycorrhizae of
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SECTION 7. PLANT PHYSIOLOGICAL RESPONSES
TO A CHANGING ENVIRONMENT
Battaglia, M, C. Beadle and S. Loughhead. 1996. Photosynthetic temperature responses of Eucalyptus globulus and
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nitrogen availability on the growth and gas exchange of
different families of jack pine seedlings. Can. J. For. Res. 27:
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Carter, K.K. 1996. Provenance tests as indicators of growth
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nutrition and climatic warming on bud phenology in Sitka
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projected climate change scenarios in forest ecosystems in
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SECTION 8. GENETIC IMPLICATIONS OF CLIMATE
CHANGE
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Microevolutionary responses in experimental populations
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Walker, B. and W. Steffen. 1997. An overview of the implications of global change for natural and managed terrestrial
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SECTION 9. CLIMATE CHANGE AND FOREST
VEGETATION DYNAMICS IN ONTARIO
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SECTION 10. THE USE OF MODELS IN GLOBAL
CLIMATE CHANGE STUDIES
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SECTION 11. FOREST MANAGEMENT RESPONSES
TO CLIMATE CHANGE
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