Authors: Marcus Lindner (EFI), Hans Verkerk (EFI)
Climate change is ongoing, and global temperatures are now more than one degree above pre-industrial levels. As well as the warming trend, extreme weather events and other disturbances have been amplified, often connected to climate change.
Recently, especially during the 2018-2020 summers, European forests have been affected by severe droughts, a series of windstorms, more severe and widespread wildfires, rapidly expanding bark beetle infestations and several other pest and disease outbreaks. Damage to forests caused by extreme events and disturbances as well as interactions between disturbances (such as bark beetle outbreaks following windstorm or drought damage) have increased in recent decades and are projected to increase under climate change. This is a major challenge for future forest management.
Climate change and associated extreme events are already affecting the growth and stability of forests in Europe. Improved forest growth has been observed in northern parts of Europe and in higher altitudes of mountainous regions (e.g. mountain treeline changes). Negative tree growth has already been reported, for example for spruce and beech in Slovakia and Belgium. Drought-induced growth declines have increasingly been observed at the dry distribution limits of tree species such as in southern Switzerland or Spain, but also in temperate lowland forests following the drought year of 2003. Forests are particularly vulnerable at the warm and dry tree species distribution limits, where intensified drought impacts and wildfire risk are particularly large and no other tree species are available to replace them.
The recent exceptionally long and intensive drought in Central Europe from 2018 to 2020 drastically exceeded previous impacts and resulted in widespread mortality in different species. It caused an unprecedented large-scale bark beetle outbreak, which affected particularly Norway Spruce forests planted outside their native range in Central Europe. This led to salvage cutting on more than a million hectares. Drought-induced mortality also affected several other species including beech and Scots pine within their native range, and partially even native mountain spruce forests. Saturated wood markets, collapsing wood prices and subsequent economic losses for many forest owners followed, especially in the Czech Republic, Austria and Germany.
In the future, forest growth and tree species composition in Europe is likely to change, but the location, the amount and partly even the direction of this change is hard to predict. This is due to a number of fundamental uncertainties regarding the:
- level of climate warming during the 21st century. Future impacts might be magnified if the world fails to meet the Paris Agreement targets.
- future evolution of extreme events in a changing climate. Some of the recent extremes were caused by changing global weather circulation patterns. It is unknown, how they will reoccur and how much worse they could get with continuing climate warming.
- effect of increasing CO2 concentrations in the atmosphere and their impact on forest growth and water use efficiency. Increasing CO2 concentrations in the atmosphere stimulate forest growth with slightly less water uptake. However, interactions with other growth limiting factors (nutrients, water) will likely reduce these effects in the future.
- combined effects of productivity changes and disturbance impacts. Climate change may enhance forest productivity in years with average climatic conditions, but these gains may be lost or even reversed due to more frequent or intensive disturbances. Therefore, it is necessary to interpret climate change impacts on productivity and disturbance regimes together. Such integrated and quantitative assessments are missing for the EU.
- adaptive capacity of land owners, trees and forest ecosystems. Locally prevailing species and genotypes get increasingly maladapted. There is only limited knowledge on how trees can adapt to novel climate conditions close to their physiological limits.
The present rate and magnitude of climate change exceeds the speed of natural tree species migration. Active management is therefore needed to enable the future existence of forests and their sustainable management. This could for example be achieved through artificial planting or seeding of better adapted genotypes or species currently not available at the site (so called “assisted migration”).