A pan-European forest mortality assessment

Forest are changing under climate change. One of the most profound changes is an increase in forest mortality, which has strong impacts on the carbon storage potential of forests as well as on forest biodiversity. Understanding the patterns and processes behind changing forest mortality is thus of utmost importance. For Europe, consistent rates and trends of forest mortality remain elusive, mainly due to a scarcity of long-term mortality monitoring sites and the challenge of harmonizing different national forest inventories. We aim to close this gap by using satellite data that is repeated pictures of the earth surface taken from space to reconstruct changes in forest mortality across Europe. While the methods for reconstructing forest mortality from space are well developed, one major challenge remaining is to identify the agent of change, that is whether tree death was caused by wind throw, bark beetle, fire or harvest. We propose to overcome this challenge by developing novel models predicting the most likely agent of change from social-ecological data (e.g., meteorological observations, species information, road access). Our hypothesis is that a fusion of ecological and socioeconomic data will significantly improve the identification of the most likely agent of forest mortality. We will subsequently utilize the developed models to create maps of forest mortality covering more than 170 million ha of forests, 32 European countries and a total of 35 years (1984 2018). Given that mortality is highly important for the future of forests and their functions, our results will be of fundamental importance for future research, including the study of European carbon stocks and biodiversity, as well as for developing simulation models predicting changes in forest mortality into the future.

Tree mortality is widely recognized as an urgent environmental issue across Europe, but data on changing tree mortality are largely lacking. In the project "A pan-European forest mortality assessment", funded by the FWF, the researchers Dr. Cornelius Senf and Prof. Dr. Rupert Seidl used more than 30,000 satellite images to unravel both rates and trends in tree mortality for all of Europe. More specifically, the two researchers of Vienna's University of Natural Resources and Life Sciences could show that tree mortality in Europe has continuously increased since 1985, with the highest canopy mortality rate of the past 34 years observed in 2018. Using simulation modeling, they further demonstrate that a continued increase in canopy mortality has the potential to largely alter forest demography across Europe's forests, which can have widespread impacts on forest carbon pools and forest biodiversity. The research team could moreover map tree mortality across all of Europe's forests, delivering the first high-resolution view on tree mortality that allows for spatially explicit analyses. For example, they show that not only the number of dying trees is increasing, but it is also larger continuous areas of trees that die. The insights and data generated in this research project will serve as important baseline for developing management strategies that increase the resilience of Europe's forests, and can serve as input to understanding the effect of increasing tree mortality on both forest carbon pools and forest biodiversity.