Senf, C. | bioRxiv Science

bioRxiv2020

Increasing canopy mortality challenges the future of Europe's forests

Pulses of tree mortality have been reported for many ecosystems across the globe recently. Yet, large-scale trends in tree mortality remain poorly quantified. Manually analyzing more than 680,000 satellite image chips at 19,896 plot locations, we here show that forest canopy mortality in Europe has continuously increased since 1985 (+1.5 {+/-} 0.28 % yr-1), with the highest canopy mortality rate of the past 34 years observed in 2018 (1.14 {+/-} 0.16 %). Using simulations, we demonstrate that a continued increase in canopy mortality will strongly alter forest demography, with the median forest age falling below 30 years in more than 50% of Europes countries by 2050. These demographic changes can have substantial cascading effects on forest regeneration, biodiversity, and carbon storage. The current trend of increasing canopy mortality is thus challenging the future of Europes forests, and should be a key priority of forest policy and management.

ecology↗

bioRxiv2020

Mapping the coupled human and natural disturbance regimes of Europe's forests

Forest disturbances shape ecosystem composition and structure, and changes in disturbance regimes can have strong consequences for forest ecosystem services. Yet we currently lack consistent quantitative data on Europes forest disturbance regimes and their changes over time. Here we used satellite data to map three decades (1986-2016) of forest disturbances across continental Europe, covering 35 countries and a forest area of 210 million ha at a spatial grain of 30 m, and analyzed the patterns and trends in disturbance size, frequency and severity. Between 1986 and 2016, 17% of Europes forest area was disturbed by anthropogenic and/or natural causes. The 25 million individual disturbance patches had a mean patch size of 1.09 ha (range between 1st and 99th percentile 0.18 - 10.10 ha). On average 0.52 (0.02 - 3.01) disturbances occurred per km2 every year, removing 77% (22 - 100%) of the canopy. While trends in disturbance size were highly variable, disturbance frequency increased and disturbance severity decreased since 1986. Changes in disturbance rates observed for Europes forests are thus primarily driven by changes in disturbance frequency (i.e., more disturbances), and only to a lesser extent by increasing disturbance size. We here present the first continental-scale characterization of Europes forest disturbance regimes and their changes over time, providing spatially explicit information that is critical for understanding the ongoing changes in forest ecosystems across Europe.

ecology↗