Forest disturbances under climate change

Disturbances are inherent to forests: drought, windthrow, fire, insects and diseases are powerful agents that weaken or kill trees. At the same time, they favor tree regenera­tion and nutrient release and contribute to increasing biodiversity. Anthropogenic climate change is likely to alter these regimes in ways that are hard to predict because of the many lags and interactions between different disturbance agents. Surpassing the historical range of variability of natural disturbance regimes, forest ecosystems may experience irreversible tipping points.

Several thousand articles reviewed

In the context of the European Cooperation's action «Towards robust projections of European forests under climate change» (PROFOUND), a group of international scientists have reviewed several thousand articles published over almost 30 years and extracted all relevant information, which was a challenge. Dario Martin Benito, postdoc from the Chair of Forest Ecology, at the Institute of Terrestrial Ecosystems, coordinated the review of drought effects on disturbances. As temperatures are rising without a corresponding increase in precipitation, drought is increasingly posing a risk to forests and the services they provide to society. Water stress disrupts tree performance and limits their ability to fix carbon and grow, and weakens their defense against pest attacks.

Increased risks for forests expected

The review suggests that drought-induced disturbances are among the most likely to increase in a warming climate, but they will be modulated by regional variations in precipitation. Changes in the frequency or severity of drought periods could increase disturbances in forests currently unaffected by water stress. Over recent decades, forests in the Valais have been affected by drought, triggering forest decline and mortality. Following tree weakening, bark beetle infestations become more frequent and damaging.