Boreal forests make up one of the largest terrestrial carbon sinks, making these forests critical to mitigating climate change. Despite their importance, there are still many unsolved questions on how a rise in temperature and altered precipitation could affect forest health, ecosystem services, and functionality as a carbon sink in the future.
Hotter and drier conditions will likely change the composition of boreal forests as temperate species move in. Although boreal forests generally respond well to disturbance, impacts from climate change might include higher frequency and intensity of wildfires, windthrow events, insects, and disease.
Reich, P.B., Bermudez, R., Montgomery, R.A., Rich, R.L., Rice, K.E., Hobbie, S.E. and Stefanski, A. 2022. Even modest climate change may lead to major transitions in boreal forests. Nature 608: 540-545.
When combined with continued land-use change, these impacts could significantly alter the environment and impact the ability of species to shift poleward. Analyzing many of these long-term effects of environmental change on is particularly challenging to accomplish in boreal forests, given the often slow pace of forest succession.
To better understand potential climate change impacts, a 5-year warming and rainfall open-air field experiment tested the response of survival and growth of nine boreal and temperate juvenile tree species to modest (1.6°C) and large (3.1°C) climate warming combined with reduced rainfall (30% below average) at two sites in northeastern Minnesota. A total of 4,600 individual trees were planted that included native broadleaf and needleleaf species that are present in the southern boreal – temperate region. Temperature was altered using infrared lamp heaters and soil heating cables, and rainfall was reduced by applying removable tarps to the study area.
The research revealed that even a +1.6°C change in temperature and reduced rainfall could increase tree mortality, especially for boreal species. Net photosynthetic response in tree species declined when soil moisture declined, suggesting that as the temperature rises, the effect on growth and survival of tree species will depend on rainfall and soil moisture availability.
Given the current trend in temperature and precipitation changes, boreal forests will likely shift in composition and closely resemble temperate forests, especially near the transition zones between southern-boreal and temperate forest. However, based on observed increased mortality and reduced understory regeneration of juvenile species, the abundance of temperate species is currently low and may be slow to colonize these areas, resulting in a fragmented landscape with reduced connectivity. Since trees often regenerate near the parent tree, range shifts might be dependent on a combination of both natural dispersion and assistance through managed redistribution.
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