Current and future drought vulnerability for three dominant boreal tree species

Area of Science:

• Forestry science
• Climate change adaptation
• Ecology

Background:

• Climate change is intensifying droughts, threatening boreal forest health and increasing tree mortality.
• Accurate predictions of forest responses to climate change are crucial for effective forest management and adaptation strategies.

Purpose of the Study:

• To identify key factors influencing drought damage risk in Swedish boreal forests.
• To predict the future spatial-temporal evolution of drought damage risk under various climate change scenarios.

Main Methods:

• Utilized tree-ring width chronologies from 16,455 cores of Norway spruce, Scots pine, and birch across Sweden (2010-2018).
• Employed a random forest machine-learning algorithm to identify predictive variables for drought damage.
• Calculated drought damage risk based on growth anomalies during 1960-2010 and projected future risks using RCP emission scenarios (2040-2070).

Main Results:

• Local climatic variables were the most significant predictors of drought damage risk, with stand competition also playing a role.
• Norway spruce exhibits high drought vulnerability in southern Sweden, projected to expand significantly with increasing spring temperatures.
• Birch vulnerability to drought is expected to increase in northern and central Sweden due to warmer annual temperatures.
• Scots pine drought damage risk is linked to cold winters and early springs, suggesting a potential decrease in risk with a warming climate.

Conclusions:

• Forest management strategies should include active species selection and promoting diverse species mixtures to enhance drought resilience.
• Reducing tree competition through methods like thinning is a promising approach to adapt boreal forests to increasing drought stress.
• Understanding species-specific responses to climate change is vital for the long-term sustainability of boreal forest ecosystems.