Environment: European forests more vulnerable to multiple threats as climate warms

More than half of Europe’s forest biomass could potentially be lost due to climate-driven natural disturbances, such as fire or insect outbreaks, reports a study published in Nature Communications. The findings may inform better forest management.

Forest trees have always been affected by disturbances such as fires, strong winds, and outbreaks of natural pests, but climate change and land transformation can enhance these threats. However, quantifying forest vulnerability to such disturbances, and their trends over time, at large geographic scales is challenging.

Giovanni Forzieri and colleagues quantify and map European forest vulnerability to three major disturbances — fire, uprooting by wind (windthrows), and insect pest outbreaks — from 1979 to 2018 by integrating disturbance data and satellite observations with machine learning-based models. Vulnerability was measured as the amount of forest biomass that is lost following a given disturbance. The authors estimate that almost 60% of the European forest biomass (over 33 billion tonnes) is vulnerable to windthrows, fires, insect outbreaks, or a combination thereof. Vulnerability to insect outbreaks in particular has grown in the past decades, especially in rapidly warming northern forests such as in parts of Scandinavia and northern European Russia, which have seen increases in insect vulnerability of around 2% per decade.

The study also identifies the forest structural properties that, depending on local climate and topographic conditions, make parts of the forest (forest stands) particularly vulnerable to the disturbances. For example, stands with taller and older trees are more prone to insect damage, especially during droughts. The findings could thus inform land management practices that would make European forests more resilient.