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Forests cover almost half of Canada's landmass, and are a key feature of our country's society, culture and economy. Climate change has the potential to greatly influence our country's forests, since even small changes in temperature and precipitation can significantly affect forest growth and survival. For example, a 1°C increase in temperature over the last century in Canada has been associated with longer growing seasons, increased plant growth, shifts in tree phenology and distribution, and changes in plant hardiness zones. Future climate change is expected to affect species distribution, forest productivity and disturbance regimes. Understanding the forestry sector's vulnerability to these changes is essential for forest management planning.
The impacts of climate change on forests would vary regionally, and would be influenced by several factors, including species composition, site conditions and local microclimate. For example, tree species differ significantly in their ability to adapt to warming, their response to elevated CO2 concentrations and their tolerance to disturbances. The age-class structure of forests is another important control on how forests respond to changes in climate. In general, forest growth would be enhanced by longer growing seasons, warmer temperatures and elevated CO2 concentrations. These benefits, however, could be offset by associated increases in moisture stress, ecosystem instability resulting from species migrations, and increases in the frequency and intensity of such disturbances as forest fires, insect outbreaks and extreme weather events. Overall, these factors lead to significant uncertainty regarding future change and make it difficult to project impacts on a regional scale.
Tree species are expected to respond to warmer temperatures by migrating northward and to higher altitudes as they have done numerous times in the past. In fact, recent warming appears to have already caused the treeline to shift upslope in the central Canadian Rockies. There are, however, concerns that species would be unable to keep up with the rapid rate of future change, and that barriers to dispersion, such as habitat fragmentation and soil limitations, would impede migration in some regions. The impacts of changing moisture conditions and disturbance regimes may also limit species migration.
The impacts of changes in disturbance regimes have the potential to overwhelm other, more gradual changes. Disturbances therefore represent a key concern for the forestry sector. Studies generally agree that both fire frequency in the boreal forest and total area burned have increased over the last 20 to 40 years. Although future projections are complicated by uncertainties regarding changes in such factors as precipitation patterns, wind and storms, severity of fire seasons is generally expected to worsen and the risk of forest fires to increase across most of the country.
Warmer temperatures are also expected to expand the ranges, shorten the outbreak cycles and enhance the survival rates of forest pests such as the spruce budworm and the mountain pine beetle. Insects have short life cycles, high mobility and high reproductive potentials, all of which allow them to quickly exploit new conditions and take advantage of new opportunities. In addition, disturbances may interact in a cumulative manner, whereby increases in one type of disturbance increase the potential for other types of disturbances. For example, in the boreal forest of western Canada, an increase in spruce budworm outbreaks could encourage wildfires by increasing the volume of dead tree matter, which acts as fuel for fires.
Adaptation will play a key role in helping the forestry industry to minimize losses and maximize benefits from climate change. Planned adaptation, whereby future changes are anticipated and forestry practices adjusted accordingly, will be especially important because rotation periods for forests tend to be long and species selected for planting today must be able to withstand and thrive in future climates. One example of planned adaptation is the use of 'fire-smart' landscapes. Fire-smart landscapes, which use such forest management activities as harvesting, regeneration and stand tending to reduce the intensity and spread of wildfire, could substantially reduce the size of future forest fires (Figure 4).
Figure 4: Size of three simulated fires on current (left) and hypothetical 'fire-smart' landscape (right) after a 22-hour fire run. Note the reduction in area burned using the fire-smart management approach. Courtesy of Natural Resources Canada
Key recommendations for facilitating adaptation include improving communication between researchers and the forest management community; increasing the resiliency of the resource base by maintaining forest health and biodiversity; and minimizing non-climatic stresses on forests.