Storms, fires and pests are becoming more common – as a result of climate change, European forests are increasingly threatened. Researchers have now systematically recorded how sensitive they actually are to the three factors: the bottom line is that half of Europe’s forest biomass is severely threatened by these disturbance variables. The data evaluations and AI-generated models also show the regional characteristics of vulnerabilities. The results could thus contribute to the development of optimized measures in the context of forest management, say the researchers.
Forests are defining elements of many European landscapes: in total they cover more than two million square kilometers – 33 percent of the surface of the continent. They influence local environmental conditions and people’s quality of life and also play an important role in global climate development by binding carbon from the atmosphere. But what about the future of Europe’s forests? Fires, storms and pests have always decimated the tree population, but in the course of climate change these pressures have increased significantly – and the trend is still increasing. It is clear in this context: Due to the long lifespan of trees, their adaptability to the comparatively rapid environmental changes is limited.
The changing forest
Some studies have already shown that climate change could cause serious problems for European forests. But so far there are hardly any comprehensive assessments of susceptibility to the primary confounding variables. As part of their study, the researchers led by Giovanni Forzieri from the European Commission Joint Research Center in Ispra have therefore quantified and mapped the susceptibility of European forests to fire, windthrow and insect pests. They used records from 1979 to 2018 on the regional pressures caused by the three variables as well as satellite observations from which large-scale changes in forest features emerged. The scientists recorded susceptibility as the amount of forest biomass that was lost after a certain disturbance. In addition, the assessments were made with the help of models based on machine learning.
The quantitative assessment showed that a total of almost 60 percent of European forest biomass – over 33 billion tons – is endangered by windthrow, fires and insect pests or a combination of these factors. In detail, it became apparent that sensitivity to storms was the most important factor at 40 percent, followed by fires at 34 percent. The researchers put the susceptibility to insect pests at 26 percent – albeit with a clearly increasing tendency. The spatial pattern of vulnerability is largely determined by the interaction between the characteristics of the forest and the background climate, the researchers explain.
Hotspot regions of vulnerability
As can be seen from the mapping, the hotspot regions of susceptibility are mainly in southern and northern Europe, where the climatic conditions for forest trees are already challenging. There is a clear trend towards greater overall susceptibility, which is characterized by a decrease in resistance due to warming, the scientists write. According to them, susceptibility to bark beetles and co. Has increased sharply in the past decades, especially in the rapidly warming northern forests. Specifically, the sensitivity to this disruptive factor has increased in large parts of Scandinavia and northern European Russia by around two percent per decade, the scientists report. According to this, stands with taller and older trees are particularly susceptible to pest infestation – especially during dry periods.
Forzieri and his colleagues are once again making it clear how intensely climate change could change our forests. By showing structural features that, depending on the local climatic and topographical conditions, shape the sensitivity of the forest stands, the study also provides new clues for the protection of forests. Depending on the importance of the respective type of threat, for example, certain tree species can be planted more strongly or special measures can be taken to strengthen the resistance. “Understanding and quantifying the susceptibility of forests to climate change-related disturbances and the underlying mechanisms is crucial in order to assess impacts and develop effective adaptation strategies,” the scientists write.
Source: Nature Communications, doi: 10.1038 / s41467-021-21399-7