Forests in climate stress
"The choice of tree species is doubly restricted today", says the lead author of the study, Johannes Wessely from the University of Vienna, "because the trees that are planted today have to be able to cope both under today's conditions and under significantly warmer conditions in the future". If, for example, thermophilic trees are planted that are well adapted to the conditions at the end of the 21st century, there is a risk of massive losses of young trees due to cold and frost in the coming years. At the same time, tree species that are well adapted to the current climate could become far too warm in the future. The intersection of species that tolerate today's and tomorrow's climate is small, and the options for forest management are correspondingly limited.
Climate change significantly reduces the number of suitable tree species
The authors of the study investigated the suitability of 69 European tree species for the whole of Europe in the 21st century. Using a new approach, they took into account the climatic suitability of a site in managed forests over the entire lifespan of the tree. The results show that climate change has reduced the set of species suitable for reforestation of current damaged areas by at least one third to one half. This means that only nine tree species per square kilometer on average in Europe are able to cope with climate change. The consequences of climate change are therefore not only forest dieback due to bark beetles and drought, but also restrictions on the reforestation of disturbed forests. According to the study, an average of 10 tree species per square kilometer in Germany are climatically fit for the 21st century, compared to 18 species under stable climate conditions.
Which and how many tree species in the different regions of Europe can withstand climate change is shown in the interactive online map.
Reduced tree species diversity reduces forest services
"This narrowing of the tree species portfolio could have a strong negative impact on important forest services," says Rupert Seidl, professor at the Technical University of Munich and last author of the study. This is because not all tree species are equally capable of providing important forest functions such as the provision of timber, carbon storage or habitat functions (e.g. as a habitat and food source for insects). Of the nine climate-fit tree species per square kilometer on average in Europe, only around a third are really capable of fulfilling these functions. Climate change and the resulting restriction in the choice of tree species may therefore lead to a significant reduction in the services provided by the forest. And the climate-related restriction of possible tree species in silviculture has another negative effect, Seidl notes: "Mixed forests consisting of many tree species are an important measure to make forests more robust against disturbances such as bark beetles. In some places in Europe, however, we could run out of tree species to establish such colorful mixed forests." The narrowing of the tree species portfolio caused by rapidly advancing climate change may therefore also reduce the ability of our forests to adapt to climate change.
Climate protection is forest protection
The choice of tree species is one of the most important decisions in forest management. The study, published in Nature Ecology and Evolution, underscores the extent to which climate change is limiting the scope for decision-making in forest management. This, in turn, can have a negative impact on the services provided by forests to society. However, the results also underline that measures that mitigate climate change significantly reduce the negative effects on forests. Effective climate protection measures are therefore of central importance in order to sustainably secure forests and their functions in Europe.
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