Climate variability drives recent tree mortality in Europe

Abstract

Tree mortality is an important process in forest ecosystems, frequently hypothesized to be highly climate sensitive. Yet, tree death remains one of the least understood processes of forest dynamics. Recently, changes in tree mortality have been observed in forests around the globe, which could profoundly affect ecosystem functioning and services provisioning to society. We describe continental-scale patterns of recent tree mortality from the only consistent pan-European forest monitoring network, identifying recent mortality hotspots in southern and northern Europe. Analyzing 925,462 annual observations of 235,895 trees between 2000 and 2012, we determine the influence of climate variability and tree age on interannual variation in tree mortality using Cox proportional hazard models. Warm summers as well as high seasonal variability in precipitation increased the likelihood of tree death. However, our data also suggest that reduced cold-induced mortality could compensate increased mortality related to peak temperatures in a warming climate. Besides climate variability, age was an important driver of tree mortality, with individual mortality probability decreasing with age over the first century of a trees life. A considerable portion of the observed variation in tree mortality could be explained by satellite-derived net primary productivity, suggesting that widely available remote sensing products can be used as an early warning indicator of widespread tree mortality. Our findings advance the understanding of patterns of large-scale tree mortality by demonstrating the influence of seasonal and diurnal climate variation, and highlight the potential of state-of-the-art remote sensing to anticipate an increased likelihood of tree mortality in space and time.

Detecting Drought-Induced Tree Mortality in Sierra Nevada Forests with Time Series of Satellite Data

“…However, a warmer and drier climate and decades of active land management have changed forest compositions and functions notably, affecting forest resilience to extreme climatic events and potentially their long term sustainability [1,[5][6][7][8]. This region experienced five consecutive years of severe drought starting in 2012, due to persistent lower-than-normal precipitation and hotter temperatures.…”

“…The growing extent of dead and dying trees poses immediate threats to public safety and creates flammable fuel for potential large and intense wildfires. Cascading effects of this massive die-off are profound and long lasting, including changes in water availability and quality, fire regimes, forest composition, species shifts, and feedback to atmospheric and climatic processes [3,8,[10][11][12][13].…”

“…Typical drivers of regional tree mortality include extreme climate variability, wildfire, insect outbreaks, and carbon starvation following hydraulic failure [5,8,[14][15][16][17]. Drought conditions induced tree mortality in California has occurred [2].…”

Tree Species Selection in the Face of Drought Risk—Uncertainty in Forest Planning

“…Climate change alters the growing conditions of forests well beyond a stand's lifespan [1]. In central Europe, projected rising temperatures, the most likely seasonal shift in precipitation and an accumulation of extreme weather events such as droughts, torrential rain and storms [2][3][4] will change tree growth and will have a considerable impact on survival rate (e.g., [5][6][7][8]). Ultimately, stand productivity and thus forest enterprise economics will be affected (e.g., [9][10][11][12]).…”

Assessment of MODIS NPP algorithm-based estimates using soil fertility and forest inventory data in mixed hemiboreal forests

“…Discrepancies between NPP SAT and the potential productivity of soil can be used for targeting the areas where the forest management practices have to be reviewed. Time series of the NPP SAT are found informative for tree mortality monitoring and predicting (Neumann et al, 2017). Regional monitoring systems e.g.…”