Impacts of climate change on forests
While average global temperatures are expected to increase by 2 to 4 degrees Celsius by 2100, projections for Canada show increases from 4 to 8 degrees Celsius, or up to four times higher than the global average. This is because Canada is a high-latitude country, and temperature changes are expected to be more severe around the poles. With forests covering nearly half of Canada’s landmass, climate change will have a profound effect on forests across the country.
When the climate changes, the forest changes
As the second largest country in the world, Canada’s landmass is wide and varied in its forest and vegetation patterns. Changes in temperature and precipitation due to climate change will affect forests differently in different regions. We have already seen changes in our forests due to the changing climate, such as the increasing survival of forest pests during warmer winters.
Canadian Forest Service (CFS) scientists are conducting research on the impacts of climate change on forests, to help forest professionals, forest-based communities and Indigenous communities understand where and how rapidly changes are occurring. This knowledge supports decisions on where and what actions might be taken.
Droughts are increasing
Drought is a powerful disturbance agent that can reduce tree growth, increase the vulnerability of trees to insects and diseases, and drive tree mortality. Historically, patchy drought is normal for Canada’s boreal forests. Certain tree species are more drought-resistant than others; for example, jack pine is one of the least vulnerable species to drought. However, if droughts are severe enough, or recur frequently, even the most resilient trees are impacted.
In recent decades, droughts have become more common and are expected to become even more frequent and severe in the future as a result of climate change. Trees experiencing drought are more susceptible to insects and disease, leading to increases in tree mortality. Drought conditions also greatly increase the risk of wildland fire. In the long-term, drought will impact tree health and regeneration success, and could lead to significant changes in forest ecosystems.
The impacts of wildfire are increasing
Fire is a dominant natural disturbance in Canada’s forests, and is a normal part of forest regeneration to maintain healthy and diverse forests. However, as the climate changes, fire weather – warmer, drier weather conditions that are conducive to wildland fire – is becoming more common, leading to longer and more intense fire seasons across Canada. Current predictions show that by 2100, the fire season in some forest regions may have lengthened by more than a month.
Because of this, more forest area in Canada is expected to burn each year. Increases in wildland fire have significant impacts on natural ecosystems and society. As fires increase, the cost of wildland fire protection grows rapidly, as do the number of wildland fire evacuations when fires get close to communities, threaten infrastructure, or when smoke endangers human health. Frequent recurrence of fires over a short time may cause failure of tree regeneration, threatening forest health as well as timber resources. Fires also release significant amounts of carbon dioxide and other greenhouse gases into the atmosphere, thereby contributing to climate change.
The patterns of forest insects and diseases are changing
Insects and diseases are a natural part of forest ecosystems, because outbreaks of native insects like spruce budworm lead to regeneration that helps maintain a healthy, diverse forest. However, because insect populations are influenced by the weather, climate change is affecting the frequency and severity of outbreaks, and is causing pests to shift northward and to higher elevations. For example, warmer winter temperatures contribute to increases in bark beetle populations because fewer beetles are killed by cold weather.
Trees have natural defences that enable them to respond and repel attacks from insects and diseases. However, droughts driven by climate change increase tree stress, making trees more vulnerable to insects and pathogens. These compounding impacts mean that many areas of Canada’s forests are seeing more damage from insects and diseases than in the past.
Growing conditions for trees are changing
Climate determines the distribution of tree species and shapes the composition of forests. When temperature and precipitation patterns are altered by climate change, the area where a tree species lives and reproduces is likely to shift to new locations. While trees are able to migrate, the rate of projected climate change is expected to be 10 to 100 times faster than the ability of trees to migrate, resulting in impacts on forest health and productivity.
Plant hardiness zones identify the location of environmental conditions under which plant species can successfully survive and grow. Climate change has already altered the geographical range of certain tree species in Canada, especially in western Canada. A tree starting to grow today in its current climate suitability zone may experience very different climate conditions when it comes to maturity.
In addition, climate change is driving permafrost thaw and is increasing the growing season across Canada. As CO2 emissions continue, it is projected that growing seasons at the end of the 21st century will be 20 to 40 days longer than those currently experienced across much of Canada. Longer growing seasons may increase tree productivity, but climate-related changes in forest pests, wildfire, droughts, and other climate extremes are expected to offset most productivity gains.
Changes in the forest mean changes for society
Forests are essential for the well-being of people in Canada, but a changing climate is putting many of the ways forests are valued at risk. Catastrophic wildland fires are particularly concerning because they pose direct threats to communities. Ecological values such as biodiversity, clean air and water, and maintenance of the global carbon balance will also be affected. For example, some wildlife habitats may disappear, shift northwards, or shift to higher elevations. These changes can affect spiritual, cultural and recreational activities.
The forest sector is a key source of prosperity for people and communities across the country. Climate change is challenging the forest sector by limiting access to forest resources and increasing operational costs. For example, transportation costs are increasing, especially in regions where winter forestry operations are the norm in Canada. More frequent wildfires and forest pest infestations are constraining local timber supplies and impacting the economic well-being of forest communities.
Integrated assessments shed light on what’s to come
Researchers at the Canadian Forest Service have conducted several integrated assessments about climate impacts, risks and opportunities. The Forest Change Story Map provides an overview of this work, including major impacts expected this century, such as:
- An overall general decline in forest productivity for most regions
- Significant increases in wildfire frequency across the northern prairies and western Quebec, with moderate increases elsewhere
- Further spread of pest disturbances, particularly for spruce budworm and mountain pine beetle
- Changes in forest composition with increasing mixed forest types along the southern boreal region and in the BC interior
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