FORESTS AND GLOBAL
Science and Technology Division
AS A CARBON SINK
OF GLOBAL WARMING ON FORESTS
FORESTS AND GLOBAL WARMING
cover almost one-half of Canadas land mass, an area representing
about 10% of the worlds forested land. They have a vitally important
place in this countrys environmental mosaic and strongly influence
climate, watersheds, wildlife and fisheries habitats. Canadas forests
also have a profound cultural and heritage value for Canadians. In 1989,
a national poll showed that three-quarters of Canadians "
the forest as a national treasure, to be held in trust for future generations."(1)
are as important to Canadas economic health as they are to the countrys
environmental integrity. The forest sector is a major provider of employment
and a major source of revenue for governments, both federal and provincial.
It follows, then, that appropriate management of the forest resource,
including its protection and regeneration, is essential to the national
"greenhouse effect," which is predicted to result in a significant
degree of global warming over the next several decades, is real. Indeed,
it is the greenhouse effect that keeps the overall average temperature
of the globe at about +15ºC. Without this phenomenon, the earth would
have an overall average temperature of -18ºC, resulting in a climate that
would be too cold and harsh for most of the life forms that characterize
the rich biological diversity of the earth today. The greenhouse gases
which contribute to the heating of the globe include carbon dioxide (CO2),
methane (CH4), nitrous oxide (NO), and the chlorofluorocarbons
relationship of Canadas forests to climate change and global warming
is significant on several levels. Some 50% of the anticipated global warming
will be caused by CO2, a ubiquitous gas which is an integral
component of the growth cycle of forests. Healthy, growing forests remove
carbon dioxide from the atmosphere and store it as organic carbon in wood
fibre. Standing forests, therefore, act as dynamic reservoirs of CO2
which can affect the concentration of atmospheric carbon dioxide. The
reverse of this beneficial biotic activity is the fact that, collectively,
forests represent a massive potential source of carbon dioxide emissions.
forests are believed to be roughly in balance with the global carbon cycle,
removing about as much carbon from the atmosphere as they contribute.
Therefore, Canadian forests will be able to moderate the onset of global
warming through sequestration of atmospheric carbon only to the extent
that forest stands can be increased in size.
significant climate warming occurs, the phenomenon will exert an important,
perhaps crucial, impact on Canadas forest resources. A warmer climate
and higher future concentrations of CO2 in the atmosphere will
affect the growth, survival, and reproduction of trees in Canadas
forests, perhaps even changing the nature, and extent of those forests.
Such changes would have a dramatic, and possibly very negative, impact
on the Canadian economy, should the harvestable stock of trees be seriously
affected under a future climate regime.
understand the significance of global warming for Canadas forests,
and the possible impacts of climate change, it is necessary to know something
of the types of forests that grow in this country. The three principal
types of forest around the world are related to climate regimes. These
are the equatorial and tropical region forests; the temperate-zone forests;
and those forests associated with colder climates. It is this last type
that predominates in Canada.
Canadian forests lie within the cold-climate boreal belt, the northern
circumpolar region which includes Alaska, the Soviet Union (Siberia),
Finland, Sweden, and Norway.(2)
Temperate-zone forests, more common to parts of the United States, extend
into Canada in milder areas along the Pacific coast and in southwestern
Ontario. In southern Ontario, the hot, humid summers have allowed the
development of a deciduous forest. Moving north through Quebec and Ontario
toward the cold-climate boreal forest, one passes through a transitional
mixed-wood forest where coniferous and deciduous trees exist in about
equal proportions. In British Columbia, a forest dominated by conifers
has developed in the cool, temperate maritime climate of the Pacific coast.
predominant boreal forest is principally composed of coniferous trees,
such as pine, spruce, larch and fir. This forest, which represents about
80% of Canadas total forested area, forms the basis of much of the
forest industry in Canada. The tree species in this region established
themselves some 10,000 years ago after the retreat of the last ice-sheets.
These trees have evolved to grow and reproduce in a climate characterized
by an extended and very cold winter interval. A change in the climate,
therefore, could have profound effects on the growth and reproduction
of conifers and could affect the species composition of this region.(3)
economy has benefited enormously from the forest resource. Currently,
the annual value of shipments from the forest sector exceeds $40 billion.
The forest products industry is the largest single industrial sector in
Canada, generating an annual trade surplus of almost $20 billion. Canada
is the worlds largest exporter of forest products and accounted
for 21% of total world trade in 1987.(4)
In 1988, the forest sector contributed 3.6% to Canadas gross domestic
has been estimated that the forestry sector provides direct or indirect
employment for some 800,000 to one million Canadians. For some 350 Canadian
communities, many in northern, rural areas, the forest industry is virtually
the only source of economic activity. In many other cities and towns,
the industry is very important to the economic base. If this resource
were to be intensively managed, as it is in some Scandinavian countries,
it has been suggested that the forestry enterprise might continue to form
not only a major part of Canadas economic activity, but could possibly
even be expanded in the future.(5)
AS A CARBON SINK
dioxide (CO2) is produced by the combustion of organic carbon
compounds, for example in the burning of wood or fossil fuels. It is also
a principal by-product of the respiration of living organisms, trees included.
In a simplified description of respiration, organic carbon molecules,
such as sugars, are combined with oxygen to release energy for lifes
functions and carbon dioxide is produced as a waste product. The decay
of plant material in the presence of oxygen will also release CO2.
dioxide is removed from the earths atmosphere by plants through
photosynthesis, a complex series of reactions that combines CO2,
water and energy from the sun to produce organic carbon compounds and
oxygen. Without photosynthesis, life on earth essentially would cease
to exist. Photosynthesis is carried out by terrestrial and aquatic chlorophyll-bearing
("green") plants. The worlds forests collectively form
a major locus of photosynthetic activity and therefore play an important
part in the earths carbon cycle and in the global-warming equation.
a tree increases in size it accumulates CO2 from the atmosphere,
converting it into the complex organic compounds in wood. As long as the
tree is alive and growing, that carbon will remain in storage; hence the
description of forests as a "sink" or reservoir for atmospheric
carbon. Forest soils store even larger amounts of organic carbon than
do forest stands. There are also large areas of peat deposits, rich in
organic carbon, throughout the northern coniferous forest zone.
most effective and efficient fixation of atmospheric carbon occurs in
the early years of a forest stand when the trees are growing rapidly.
At the early stage of growth, trees accumulate more carbon through photosynthesis
than they release through respiration. As the stand ages, however, the
amount of carbon released through respiration increases. Eventually, the
balance will shift to a net loss of carbon to the atmosphere as the sum
of carbon emitted through respiration and decay exceeds that sequestered
when the stand reaches advanced age and the trees begin to die, the balance
will shift predominantly to carbon loss. This observation does not mean,
however, that old-growth forests should be cut and replanted with seedling
trees for the purpose of increasing the carbon sink. Old-growth forests
have intrinsic ecological and cultural values, and a considerable body
of evidence indicates that they should be left intact.
a tree is cut, some of the carbon may be released back to the atmosphere
fairly quickly as the small limbs, bark, foliage, etc., are discarded
and burned, or allowed to decay on the forest floor. Similarly, a tree
burned in a forest fire will quickly release a large quantity of carbon
dioxide, together with a mixture of other gases.
the tree is used in construction or in other relatively permanent products,
the carbon will remain trapped in the wood, perhaps for decades or centuries.
If, however, the wood is burned as fuel, or is converted into papers or
chemicals which have a limited temporal use-cycle, all of the trees
accumulated carbon may be emitted to the atmosphere in a relatively short
period of time.
issues of reforestation and deforestation are very important in a consideration
of global warming. Reforestation refers to the replanting of trees in
a commercial forest after harvest. Deforestation occurs when forested
land is converted to other permanent uses, such as agriculture or settlement.
Deforestation thus contributes to increasing concentrations of atmospheric
CO2, partly through a reduction in global photosynthetic activity,
and partly through the release of the carbon stored in the forest biomass.
Most of the worlds attention to deforestation is focused on tropical
countries, particularly the rainforest of Brazil.
management is essential to maintain a healthy, productive forest for commercial,
recreational, and ecological reasons. In the context of global warming,
forest management gains additional importance because a well-managed,
vigorously growing forest will sequester carbon more efficiently than
a poorly managed stand. Efficient forest management can be a part of the
solution to the developing global-warming scenario, particularly the prompt
regeneration of harvested areas, either through planting or by natural
means, and the reduction of losses of stands to wildfire, insects and
disease. The extensive commercial harvesting of trees and the loss of
trees from other causes in the developed countries, Canada included, has
not always been followed by adequate replanting of stock.
an appearance before the House of Commons Standing Committee on Environment,
Dr. J.S. Maini of Forestry Canada stated that there are 244 million hectares
(ha) of inventoried productive forest land in Canada. Of this total, 7%,
or 17 million ha, were classified as "NSR" in 1989. Land that
is classified as NSR is:
not satisfactorily (or sufficiently) restocked (or revegetated),
productive forest land that has been denuded and has failed partially
or completely to regenerate naturally or to be artificially regenerated.
The regeneration must contain a minimum number of well-established,
healthy trees free-to-grow, sufficient to produce a merchantable
timber stand at rotation age.(6)
key component of this definition is that the trees must form a commercial
stand in order not to be regarded as NSR. Although most of these NSR lands
are not currently supporting stands of trees of commercial quality, they
are covered by foliage of some sort which is sequestering some atmospheric
carbon. Dr. Maini informed the Committee that, while reforestation of
these 17 million ha would make only a modest contribution to the global
carbon balance, it could be a significant factor in Canadas national
their appearance before the Standing Committee on Environment, Forestry
Canada officials stated that the situation with Canadas NSR lands
has improved recently: "
during the last five years, through
cost-shared programs with the provinces, we have spent about $1 billion
in reforestation programs and have planted about 1.3 billion seedlings,
and almost 1 million hectares have been treated in the country."(8)
The question of NSR backlog remains, however. In 1988, for example, there
was a shortfall of 198,000 hectares of forest land that were not regenerated
after harvest, either by seeding or through natural processes.(9)
Canadas testimony to the Environment Committee also stated that
the federal government would participate with the provinces in replanting
the NSR backlog, "
provided the provinces and the industry
look after the current cutters."(10)
The Director of Forestry Development for Forestry Canada suggested that
if no more NSR lands were created, and if funding through federal-provincial
forestry agreements were directed totally at backlog, then, with "
a sustained level of planting the backlog could probably be rehabilitated
within 10 or 20 years.(11)
the context of forest management and the restocking of NSR lands, the
matter of federal-provincial forestry agreements is important. Most of
Canadas forested areas fall under provincial jurisdiction. The principal
type of federal-provincial forestry agreement in Canada is the "Federal-Provincial
Forest Resource Development Agreements" (FRDA) which are administered
by the federal and provincial governments. In 1989, there were FRDAs between
the federal government and the governments of Newfoundland, Nova Scotia,
Prince Edward Island, Ontario, Saskatchewan, Alberta, and British Columbia.
The federal government also signed agreements other than FRDAs with New
Brunswick, Quebec and Manitoba.
of the federal-provincial forestry agreements have now expired, including
the FRDAs with Ontario, Saskatchewan and Alberta (31 March 1989) and those
with Newfoundland and British Columbia (31 March 1990). The non-FRDA agreements
with Quebec and Manitoba have also expired. New agreements were signed
with Nova Scotia and New Brunswick near the end of March 1990. In February
1991, it was announced that a new FRDA had been negotiated between the
federal government and British Columbia. New agreements with the other
provinces are currently under negotiation.
in a forested area, whether wildfire or controlled burning, has an obvious
relevance to the global warming issue: fires result in the rapid liberation
of large amounts of CO2 and smaller amounts of other gases,
including methane, a much more potent greenhouse gas than carbon dioxide.
Destruction of forest stands will also reduce the total amount of photosynthesis
and therefore contribute to an increase in atmospheric concentrations
is incorrect, however, to conclude that fires are entirely destructive
and negative events in the forest environment. The boreal forest has evolved
with fire as a frequent and significant environmental factor:
overwhelming impact of wildfires on ecosystem development and
forest composition in the boreal forest is readily apparent and
understandable. Large contiguous expanses of even-aged stands
of spruce and pine dominate the landscape in an irregular patchwork
mosaic, the result of periodic severe wildfire years and a testimony
to the adaptation of boreal forest species to natural fire over
millenia. The result is a classic example of a fire dependent
ecosystem, capable, during periods of extreme fire weather, of
sustaining the very large, high intensity wildfires which are
responsible for its existence.(12)
fires, particularly in areas remote from human settlement, can cover enormous
areas. The so-called Great China Fire in the early spring of 1987 on the
China-USSR border burned over 1.1 million hectares. At the same time there
were much larger fires burning in the boreal forests of Siberia in the
USSR, some covering an area of 2 million ha. In total, up to 50 fires
in Siberia in 1987 are estimated to have consumed approximately 10 million
hectares of forest.
fire incidence in Canada has been extensively studied, and detailed fire
statistics have been collected since 1920. The data show that the annual
fire frequency has increased steadily over the last six decades, from
about 6,000 fires annually in the 1930-1960 period, to almost 10,000 fires
annually during the 1980s. The increasing numbers of fires have been ascribed
to the impact of a growing Canadian population and increased forest use,
as well as to an expanded capability for detecting fires in more remote
number of fires does not necessarily give an indication of the area burned,
and in fact that area fluctuates tremendously each year. From 1920 to
1960, the area burned by forest fires in Canada actually decreased; however,
it increased dramatically during the 1980s, primarily as a consequence
of periods of short-term extreme fire weather in western and central Canada.
The annual average number of fires and area burned in Canada for the 1980-1989
period were 9,618 and 2.44 million ha, respectively. In 1989, the worst
fire year on record, there were more than 11,000 fires in Canada and the
burned area was greater than 6.4 million hectares.(13)
of September 1990, the 1990 fire season in Canada was described as "average,"
with 9,057 fires being reported.(14)
Total hectarage, at 839,570 ha in lost stands, was well below the average
for the 1980-1989 period. Much of the hectarage lost in 1990 was in Western
Canada, with the Yukon and Northwest Territories and Saskatchewan accounting
for 51.6% of the total area burned. Manitoba, which was the location of
enormous fires in 1989, recorded 482 fires and a total of 16,794 ha burned.
As is typical in forest fire scenarios, a relatively small number of fires
accounted for the bulk of the area burned: in 1990, 4% of the fires burned
54.6% of the hectarage.
relationship between forest fires and multiple uses of the forest by Canadians
is reflected in the statistics on causes of fires: some 65% of fires are
caused by human activities and the remainder, 35%, by lightning. However,
this latter cause accounts for 85% of the area burned because such fires
occur randomly and in more remote areas. This delays detection of the
fire and makes access difficult for fire-fighters, thereby frustrating
quick initial attack and allowing the fire to become well established
before mitigation efforts can be brought to bear.
fire fighting in Canada has become a highly developed activity, and this
is reflected by the fact that the vast majority of fires are controlled
early; only 2-3% of forest fires in Canada grow larger than 200 ha and
these fires account for 97-98% of the total area burned. Over the past
seven decades, the percentage of smaller fires has increased steadily
while the percentage of larger fires has declined, a tribute to the success
of fire-management programs.
many jurisdictions in Canada decisions have been made to allow fires in
low-priority areas to run their course, priority being defined on the
basis of human values assigned to the forest resource. In Ontario in the
1980s, this resulted in an increased number of larger fires in such areas.
The decision has been based partly on economic considerations; remote
fires are extremely expensive to fight.
Also, fire, as stated earlier,
is a natural component of the boreal ecosystem and plays a dynamic role
in forest reproduction and renewal. It should also be noted that when
a forest burns in a wildfire, not all of the organic carbon stored in
the trees is released to the atmosphere. The portion of the tree below
ground (the root system), estimated to comprise about 30% of the total
biomass, typically does not burn.
Also, it is estimated that
on average only about 20% of the above-ground portion of the tree actually
burns, the rest remaining as soil organic matter, or as long-lasting charcoal.(15)
Therefore, given that fire in the boreal forest makes a positive contribution
to forest renewal, it is possible that forest fires might ultimately result
in a net accumulation of carbon in biomass.
Before the onset of very
favourable conditions for fire in the last decade, it was generally believed
that damage from fires would continue to decline in this country with
improved forest fire management and control. That this has not happened
is a portent of what might take place should fire conditions continue
to worsen under a new climate regime.
There is now a general awareness
within the scientific, and even the political, community that the global
burning of biomass has a significant impact on the composition of the
atmosphere and on climate warming. While most world attention is focused
on the destruction of forests and biomass burning in tropical regions,
research is also underway to determine the impact of biomass burning in
the northern hemisphere. For several years, Canada and the United States
have been cooperatively studying the behaviour and atmospheric environmental
impact of large-scale fires in Canadas boreal forest zone.
One result of this research
has been the characterization of smoke chemistry associated with fires
in the boreal forest. When combined with fire statistics, the data have
been used to generate estimates of the contributions of northern hemisphere
forest fires to trace gases in the earths atmosphere. Of the total
amount of carbon released during a fire in the boreal forest, 89% is in
the form of CO2 and 9% is carbon monixide. The remaining 2%
is released as methane (CH4) or non-methane hydrocarbons. The
following figures, expressed as grams of gas released per kilogram of
carbon burned, have been estimated: carbon dioxide, 1500 g/kg; carbon
monoxide, 150 g/kg; methane and total non-methane hydrocarbons, 15 g/kg.
By combining these figures
with statistics on the area of forest burned in the northern circumpolar
region, estimates have been derived for total trace gas emissions from
the regions forest fires. Approximately 70 Teragrams (Tg = trillion
grams, or 1 million tonnes) of carbon are consumed in fires annually,
on average. This equates to releases of 105 Tg of carbon dioxide; 10.5
Tg of carbon monoxide; and 1.1 Tg of both methane and non-methane hydrocarbons.
These figures have to be
viewed in the context of total global emissions of greenhouse gases from
biomass burning. The most recent estimate of global biomass burning indicates
that 2,000-5,000 Tg of carbon are released each year, the primary contributors
being savannah (tropical grassland) burning and the deforestation of tropical
areas. Thus, forest fires in the northern circumpolar region contribute
about 1.4-3.5% of the carbon released worldwide through biomass burning,
assuming that the various estimates are accurate.(16)
Forestry Canada has been
developing estimates of the carbon balance of Canadas forest lands;
that is, the balance between the carbon released from the forest through
respiration, wildfire, commercial harvest, the impacts of insects, disease
and other disturbances, and the amount of carbon sequestered by foliage
from the atmosphere. Obviously, this is an enormous, and enormously difficult,
proposition, given the immense hectarages involved and the large number
of species of trees and other plants.
Nonetheless, the carbon
balance of Canadian forests has been estimated, using data from 1986.
This work indicates that Canadas forests had a total carbon inventory
of 225 billion tonnes, and that there was an excess of carbon accumulation
over carbon emissions of 116 million tonnes. Two points should be kept
in mind, however. First, the amount of net carbon accumulation for the
reference year is very small in relation to the total stored in the forest
just over 0.05%. Second, a change in forest conditions, such as
the very severe fire situation that developed in 1989, would change the
balance to that of a net carbon source. For these reasons, Canadas
forests are assumed to be roughly in balance with the global carbon cycle.(17)
In the context of the burning
of forest biomass, it is appropriate to consider the matter of slashburning,
also known as "prescribed fire," which is used in silvicultural
programs to prepare harvested forest sites for replanting. Prescribed
burning of slash wood residue and litter on the forest floor after harvest
releases significant quantities of carbon dioxide and other gases to the
The practice is well-established
in British Columbia and Ontario, with the former being by far the greater
user of the technique. In British Columbia, prescribed burning takes place
on more than 100,000 ha each year - 137,596 ha in 1989, burning on just
over 73,000 ha of which was for silviculture purposes. The remaining hectares
included large areas for range and wildlife habitat improvement. In Ontario,
the total prescribed burned area averages less than 10,000 ha per year,
mostly in the boreal forests of northern Ontario, away from major population
Slashburning for silviculture
has been practised in B.C. since the early 1900s and is currently regulated
in the province by the B.C. Forest Service under a permit system. For
silviculture, slashburning is carried out "to reduce fire hazard,
facilitate planting, provide a favourable environment for seedlings, and
to eliminate diseases such as dwarf mistletoe."(19)
As well as releasing smoke and greenhouse gases, the practice may also
have other negative impacts, including possible reduction of long-term
nutrient supply and soil organic matter at the site, and elimination of
Significant quantities of
CO2 are released directly through slashburning; however, if
this material is not burned, it will eventually decompose on the forest
floor and release its carbon through biological, rather than physical,
processes. The time scale will be longer, but the result will be similar.
It must also be kept in mind that prescribed burning for silviculture,
like wildfire in the boreal forest, is followed by regeneration of the
The new forest will sequester
atmospheric carbon, converting it into wood through photosynthesis. Whether
the amount of carbon recovered by the new managed forest will ultimately
be greater than, less than, or equal to that recovered by an unmanaged
forest will depend on a number of factors. However, it is certain that
the total contribution of CO2 to the atmosphere from slashburning
will be significantly less than that suggested by emission levels alone.
OF GLOBAL WARMING ON FORESTS
The discussion of the possible
impacts on Canadas forests of increases in global temperature and
climate change must commence with a clear recognition that there are enormous
uncertainties associated with the various scenarios that have been advanced.
However, there is a good consensus within the scientific community that
some warming of the earth is probable and that regional climates will
change in the future. The boreal forest, which forms the basis of much
of Canadas forest resource and the industry it supports, is very
sensitive to climate change:
The structure and
function of the boreal forest ecosystem is more clearly dependent
on climate than many other ecosystems. Many characteristics of
the boreal forest, including tree physiology and productivity,
vegetation zones, fire, and insects and diseases are inextricably
linked to climate.(21)
With a doubling of carbon
dioxide in the atmosphere (the "2 x CO2" scenario),
the earths surface temperature might increase by 1.5-4.5°C; this
could happen by 2030 under a "business-as-usual" scenario, or
as early as 2015 under a high-emission scenario. The effects will be even
more severe in northern regions, particularly in Ontario and Quebec: temperature
increases of "perhaps up to ten degrees or more are expected in parts
of the boreal forest."(22)
This level of warming occurring over the next century would represent
a rate of climate change ten times more rapid than forest trees and ecosystems
have experienced during the past 10,000 years.(23)
The effect of climatic change
on Canadas ecosystems is currently the subject of research at Environment
Canada using a "climate-ecosystem response model" which permits
the development of ecological scenarios under various climate regimes.
In January 1990, the department published a report on the "ecoclimatic
provinces" of Canada under current conditions and under the warmer
climate anticipated in 2050.(24)
Table 1, taken from this report, lists the projected real changes, while
Figures 1 and 2 illustrate the current and projected ecoclimatic provinces
on a map of Canada.
Area of Canada (%)
Source: Brian Rizzo, "The
Ecosystems of Canada in 2050: a Scenario of Change," State of
the Environment Reporting, Newsletter No. 5, Environment Canada, January
1990, p. 4-5.
For forestry, the most dramatic
changes will be in the size and location of the boreal forest ecoclimatic
province. The boreal forest, currently occupying a wide swath that sweeps
across Canada from Newfoundland to the Rocky Mountains and Alaska, making
up some 82% of Canadas forested area, is projected to shrink by
14%. At the same time, the cool temperate and moderate temperate climatic
zones, currently covering only small southern areas of Canada, will grow
to 15% and 5% of Canadian territory, respectively. Similarly, the grassland
zone is projected to expand to 12% of total area from its current 5%.
In rough terms, the climatic
zone favouring the boreal forest will move much farther north and the
temperate climate zone, which supports a deciduous forest, will expand
northwards from its current restricted area in the southeast of Canada.
The ecoclimate of Newfoundland will change from maritime boreal to moderate
temperate, an ecoclimatic zone currently found only in southern Ontario.
Dr. J.S. Maini of Forestry
Canada gave the Environment Committee a rough estimate of the impact of
climate warming on Canadas forests:
One of the things
we have projected in Canada is that for everyone degree centigrade
change in temperature, the belts of forests, the boreal forests,
the hardwood forests, the mixed wood forests, are likely to shift
about 100 kilometres.(25)
Source: Brian Rizzo, "The
Ecosystems of Canada in 2050: a Scenario of Change," State of
the Environment Reporting, Newsletter No. 5, Environment Canada, January
1990, p. 5.
The Intergovernmental Panel
on Climate Change (IPCC) provides the following, more detailed projection,
based on computer simulations:
Under the GISS 2
x CO2 climate scenario the circumpolar boreal forest
could shift some 500-1000 km northwards
The southern boundary
of the Canadian boreal forest could shift some 470-920 km north,
and the northern boundary some 80-720 km north
GFDL scenario, however, the respective potential shifts could
be 250-900 km and 100-730 km northward. Projected losses of potential
boreal forest sites in the Canadian south could amount to 170
million ha, while gains in the north could amount to 70 million
, a net loss of 100 million ha.(26)
The time frame involved
in a change in the type of forest is open to speculation. Although the
climate in a particular region may become altered, it could take many
decades, or even longer, for the species composition of a forest to change.
A dramatic event such as a forest fire could, however, hasten such a change.
There are a number of factors
which will be brought to bear on the productivity of Canadian forests
in a warmer climate. It is impossible to be specific about the effects
of any of these factors, but for purposes of policy assessment and planning
it is essential to be cognizant of them.
It has already been noted
that there could be a change in the zonal climates in Canada, with large
areas becoming more suitable for deciduous or mixed wood forests, or grasslands,
rather than for boreal species. Some areas could see faster tree growth
as a consequence of warmer climate. Similarly, there could be a "fertilizer
effect" from higher atmospheric CO2 concentrations which
would increase a trees photosynthetic rate, and therefore its rate
of growth. It is not certain, however, that this will occur; the fertilizer
effect of higher CO2 concentrations has been demonstrated with
seedling trees but it is not known if mature trees will respond in the
Paradoxically, a warmer
climate may result in an increase in winter damage to some tree species.
If a warmer climate produces a decrease in snowfall, the frost may penetrate
deeper into the ground and damage tree roots. This type of damage has
already been implicated in the decline and death of hardwood trees in
Canada. The current serious decline of sugar maple forests and other hardwood
species in eastern Canada may be due, at least in part, to this phenomenon.(27)
Forest productivity is generally
higher in warmer, moister climates. In some areas of Canada, moisture
may well become a limiting factor in parts of the forest ecosystem where
lower levels of precipitation accompany increased temperatures, bringing
about a decrease in forest productivity. Also, while the warmer climate
theoretically may move the forest zone farther north, the actual development
of forests in more northern regions will be subject to the availability
of appropriate soil conditions. It is also possible that some northern
lands in the Canadian prairies, now marginal for agriculture, could become
more productive. If agriculture begins to encroach on existing forest
lands, land-use conflicts between agriculture and forestry could arise.
The matter of forest diseases
and insects is another concern. The activities of some species of insect
pests prevalent in the United States are restricted in Canadas colder
climate. Insect populations will certainly change in number and type with
climate warming, very possibly to the detriment of the forest resource.
One possible future pest is the balsam woolly aphid, a sucking insect
which attacks balsam fir and damages the wood quality by staining the
cells and which may also cause tree mortality. The distribution of this
insect pest is currently restricted by cold winter temperatures but the
situation might change with global warming.
A second example is the
eastern spruce budworm, an extremely serious insect pest which causes
defoliation of a number of valuable conifer species, including balsam
fir, white spruce, hemlock, and eastern larch. The budworm causes extensive
tree damage and mortality in evergreen forests east of the Rock Mountains.
In 1986, 25 million hectares of forest were dead or dying as a consequence
of attacks by this insect.(28)
Budworm epidemics are usually preceded by two to three years of warm,
dry spring weather, a scenario that might become more typical with global
Diseases in Canadian forests
yearly extract a significant toll in tree damage and mortality. As is
the case with insects, many of these root and stem diseases are limited
in distribution and severity by low temperatures, a situation that could
change with climate warming. If a warming climate causes forest ecosystems
to become progressively less well-suited to their environments, increasing
areas of forest will become stressed, a situation that typically renders
trees more susceptible to attack by disease organisms, as well as by insect
Forest ecosystems evolve
very slowly, unlike grasslands or agricultural crops. Also, as was noted
earlier, the pace of projected global warming will be unprecedented:
recognize that forests
are long living ecological entities.
Many of our forests are 500, 700, 1,000 years old. In British
Columbia there are many cases where you have forests more than
1,000 years old
the rate of (climate) change, which is
likely to be 10 times more than what we have experienced over
the last 10,000 years, is very crucial when we determine the likely
impact on forests. Our forests have not had the experience of
that kind of change.(29)
It was pointed out earlier
that the tree species that now populate the Canadian boreal forest evolved
in a cold climate. A warming of the climate could adversely affect their
growth and reproduction. They would also be at a competitive disadvantage
with respect to species that have evolved in a warmer climate. This might
not have a major effect on standing stock but could have serious impacts
on reforestation, whether accomplished through natural means or through
While annual agricultural
crop species can be improved and adapted fairly quickly to new environmental
conditions through breeding programs, the same is not true for forest
In forestry, using
the traditional breeding strategies it takes us 15 years before
the trees even start flowering. So (to develop) the next generation
of breeding of trees that are adapted to warmer or drier conditions
we really need a much longer lead time than agricultural
Reforestation programs in
Canada and elsewhere are proceeding apace at a cost of hundreds of millions
of dollars. While such programs are essential to the regeneration of growing
stock for a variety of purposes, there is a potential flaw in the planning,
should global warming become significant in the next century. Current
reforestation efforts utilize seedlings whose genetic characteristics
are selected and matched to the geographic locale and the present climate
regime. As Maini has noted, the match between climate and genetic traits
may not hold:
In Canada, for example,
seedlings being planted today, at considerable cost, will be only
half their commercially harvestable age by the year 2030, when
they could be growing in a very different climate. We need to
develop strategies to protect this investment for example,
by developing technologies to harvest and use smaller trees.(31)
An important variable in
the overall forestry equation, which could have an enormous impact on
standing stock and thus on the future makeup of Canadas forests,
is forest fire. The dramatic increase in the numbers of wildfires in Canadas
forests in 1989, particularly in Manitoba, where huge areas of forest
were burned, gave an indication of what can happen in the boreal forest
under warm, dry climatic conditions. As was noted above, however, wildfire
has been an integral part of the boreal forest ecosystem and the current
mix of coniferous species in the boreal forest reflects the selective
impact of past fires.
Under a warmer climate regime,
wildfire may have a quite different impact. The conifers that now populate
the boreal zone, and upon which much of Canadas forest industry
is based, have evolved in, and become adapted to, a climate significantly
cooler than that which is anticipated to lie 50 or 70 years in the future
as a consequence of global warming. In a changed climate regime, wildfire
could effect significant species change in the boreal forest:
predicted that fire will act as a major agent in removing vegetation
types that are no longer adapted to the changed climatic conditions,
setting the stage for new combinations of plant species to invade
It is possible, then, that
the character of the boreal forest could change fairly rapidly if wildfires
become a major problem under a warmer climate regime. If major conflagrations
do become a common occurrence in the boreal forest, very large amounts
of CO2 and other gases will be liberated. Depending on their
magnitude, these wildfires could frustrate efforts to reduce the concentration
of CO2 in the atmosphere through restrictions on combustion
of fossil fuels and other mitigative measures.
The importance of forests
to Canada, both in economic and environmental terms, is indisputable.
A warmer global climate may well have profound effects on the Canadian
boreal forest, and at least some of these effects will not be beneficial.
Climate change will have many implications for Canadian society and it
is clear that both mitigative and adaptive strategies and programs will
have to be designed now for implementation as changing circumstances dictate.
With the state of current
knowledge of climatic processes and climate change, it is not possible
to predict the extent or rate of projected effects of anthropogenic origin.
Given the large predictive uncertainties, the appropriate course of action
for the Canadian forest sector is to develop policies and strategies that
make good sense under the current climate regime but will also be appropriate
in a warmer climate scenario.
Appropriate forest management
programs based on sound science are essential whether the climate changes
in the next century or remains substantially the same as it is now. The
development of such visionary programs will require an increased and firm
commitment of funds by industry and by provincial and federal governments.
approach is not acceptable in the context of pollution control as it has
become very clear that the anthropogenic emissions of greenhouse gases
and other pollutants must be substantially reduced, both to prevent (or
at least slow the rate of) possible global warming, and to reduce impacts
on the biophysical environment and human health. Effective mitigative
actions must be introduced on both a national and global scale.
The business-as-usual approach
is also not appropriate for the management of Canadas forest resource.
Forest management policies more effectively geared to the sustainability
of forests are needed. The programs that are developed out of such policies
must optimize the economic and environmental potentials of Canadas
forests and must also be cognizant of the imminent possibility of climate
change in the present boreal forest regions.
Crutzen, Paul J.
and Meinrat O. Andreae. "Biomass in the Tropics: Impact on Atmospheric
Chemistry and Biogeochemical Cycles." Science, Vol. 250, 21
Forestry Canada. Strategic
Plan for Research on Climate Change 1990-1995. Science Directorate,
21 March 1990.
Forestry Canada, "Does
Slashburning Increase Atmospheric Carbon Dioxide Levels?" Focus
on Forestry, June 1990.
Forestry Canada. 1991-92
Estimates, Part III Expenditure Plan.
House of Commons. Minutes
of Proceedings and Evidence of the Standing Committee on Environment.
Issue No. 22. 21 November 1989.
House of Commons. Forests
of Canada: The Federal Role. Report of the Standing Committee on Forestry
and Fisheries, Sub-Committee on Forestry. Bud Bird, M.P., Chairman, November
1990, 171 p.
on Climate Change. Draft Report of Working Group 2. Likely Impacts
of Climate Change. Geneva, 1990.
Lawson, Bruce D. "Where
There Is Fire, Theres Smoke: A Global View of B.C.s Prescribed
Burning." Presentation at Panel Discussion on Smoke Management. Southern
Interior Fire Management Committee, Cranbrook, B.C., 2 June 1990.
Maini, J.S. "Forests:
Barometers of Environment and Economy." In Constance Mungall and
Digby J. McLaren (editors). Planet Under Stress The Challenge
of Global Change. Royal Society of Canada, 1990.
Rizzo, Brian. "The
Ecosystem of Canada in 2050: a Scenario of Change." State of the
Environment Reporting. Newsletter No. 5. Environment Canada, January
Ross, W. Wein and Edward
H. Hogg. "Climate Change Moisture Stresses on Northern Coniferous
Forests." In: G. Wall and M. Sanderson (editors). Climate Change:
Implications for Water and Ecological Resources. Occasional Paper
No. 11. Department of Geography, University of Waterloo, Ontario, 1990.
Stocks, Brian J. "The
Extent and Impact of Forest Fires in Northern Circumpolar Countries."
Chapman Conference on Global Biomass Burning: Atmospheric, Climatic, and
Biospheric Implications. Williamsburg, Virginia, 19-23 March 1990 (in
Wheaton, E.E. and T. Singh.
"Exploring the Implications of Climatic Change for the Boreal Forest
and Forestry Economics of Wetern Canada." Climate Change Digest,
CCD 89-02, Environment Canada, 1989.
Environics Research Group Limited, 1989 National Survey of Canadian
Public Opinion on Forestry Issues Final Report, Prepared for
Forestry Canada, Toronto, May 1989, p. 9-10.
The word "boreal" means related to, or growing in, the northern
parts of the northern hemisphere.
C.R. Stanton, "Forest," The Canadian Encyclopedia, Second Edition,
Volume II, Hurtig Publishers, 1988, p. 810.
J.S. Maini, "Anticipated Climate Change and Forests," Forestry
Canada, Background Notes for Presentation to the Standing Committee on
Environment, 21 November 1989a.
House of Commons, Forests of Canada: The Federal Role, Report of
the Standing Committee on Forestry and Fisheries, Sub-Committee on Forestry,
Bud Bird, M.P., Chairman, November 1990, p. 2.
J.S. Maini (1989a).
J.S. Maini, House of Commons, Minutes of Proceedings and Evidence of the
Standing Committee on Environment, Issues No. 22, 21 November 1989b, p.
Forestry Canada, 1991-92 Estimates, Part III Expenditure Plan,
J.S. Maini (1989b), p. 22:16.
John Forster, House of Commons, Minutes of Proceedings and Evidence of
the Standing Committee on Environment, Issue No. 22, 21 November 1989,
Brian J. Stocks, "The Extent and Impact of Forest Fires in Northern
Circumpolar Countries," Chapman Conference on Global Biomass Burning:
Atmospheric, Climatic, and Biospheric Implications, Williamsburg, Virginia,
19-23 March 1990 (in press). [unless otherwise indicated, the data presented
below are from this paper]
Brian J. Stocks, "Global Warming and the Forest Fire Business in
Canada," Canada/United States symposium on the Impacts of Climate
Change and Variability on the Great Plains; Calgary, Alberta, 11-13 September,
1990b (in press).
Forestry Canada, Personal Communication, February 1991.
W. Seiler and P.J. Crutzen, 1980: quoted in Christopher P. Da Silva, "Role
of the Canadian Forests in the CO2 Issue," Canadian Climate Centre,
Environment Canada, 1 May 1982, p. 18.
Paul J. Crutzen and Meinrat O. Andreae, "Biomass Burning in the Tropics:
Impact on Atmospheric Chemistry and Biogelchemical Cycles," Science,
Vol. 250, 21 December 1990, p. 1669-1678. (Also, quoted in Brian J. Stocks,
Forestry Canada, Personal Communication, March 1991.
Bruce D. Lawson, "Where There Is Fire, Theres Smoke: A Global
View of B.C.s Prescribed Burning," Presentation at Panel Discussion
on Smoke Management, Southern Interior Fire Management Committee, Cranbrook,
B.C., 2 June 1990, p. 2.
Forestry Canada, "Does Slashburning Increase Atmospheric Carbon Dioxide
Levels?," Focus on Forestry, June 1990, p. 1.
Peter Fuglem, "Prescribed Burning in British Columbia," B.C.
Forest Service, Unpublished Note, 19 July 1990.
E.E. Wheaton and T. Singh, "Exploring the Implications of Climatic
Change for the Boreal Forest and Forestry Economics of Western Canada,"
Climate Change Digest, CCD 8902, Environment Canada, 1989, p. 2.
Forestry Canada, Strategic Plan for Research on Climate Change 1990-1995,
Science Directorate, 21 March 1990, p. 1.
J.S. Maini (1989b), p. 22:8.
Brian Rizzo, "The Ecosystems of Canada in 2050: a Scenario of Change,"
State of the Environment Reporting, Newsletter No. 5, Environment Canada,
January 1990, p. 4-5.
J.S. Maini (1989b), p. 22:9.
Intergovernmental Panel on Climate Change, Draft Report of Working Group
2, Likely Impacts of Climate Change, Chapter 2, Section 3.4.1,
1990. (GISS is an acronym for the Goddard Institute for space Studies;
GFDL is an acronymfor the Geophysics Fluid Dynamic Laboratories.)
J. Peter Hall, "How Will the Projected Changes in Canadas Climate
Affect the Sustainability of our Forests?," Forestry Canada, unpublished
paper, 3 January 1991, p. 9.
Ibid., p. 14.
J.S. Maini (1989b), p. 22:8.
Ibid., p. 22:1011.
J.S. Maini, "Forests: Barometers of Environment and Economy,"
in Constance Mungall and Digby J. McLaren (eds.), Planet under Stress
The Challenge of Global Change, Royal Society of Canada, 1990,
Ross W. Wein and Edward H. Hogg, "Climate Change Moisture
Stresses on Northern Coniferous Forests," in G. Wall and M. Sanderson,
eds., Climate Change: Implications for Water and Ecological Resources,
Occasional Paper No. 11, Department of Geography, University of Waterloo,
Ontario, 1990, p. 286.