Significant increase in natural disturbance impacts on European forests since 1950

Abstract

Over the last decades, the natural disturbance is increasingly putting pressure on European forests. Shifts in disturbance regimes may compromise forest functioning and the continuous provisioning of ecosystem services to society, including their climate change mitigation potential. Although forests are central to many European policies, we lack the long-term empirical data needed for thoroughly understanding disturbance dynamics, modeling them, and developing adaptive management strategies. Here, we present a unique database of >170,000 records of ground-based natural disturbance observations in European forests from 1950 to 2019. Reported data confirm a significant increase in forest disturbance in 34 European countries, causing on an average of 43.8 million m³ of disturbed timber volume per year over the 70-year study period. This value is likely a conservative estimate due to under-reporting, especially of small-scale disturbances. We used machine learning techniques for assessing the magnitude of unreported disturbances, which are estimated to be between 8.6 and 18.3 million m³ /year. In the last 20 years, disturbances on average accounted for 16% of the mean annual harvest in Europe. Wind was the most important disturbance agent over the study period (46% of total damage), followed by fire (24%) and bark beetles (17%). Bark beetle disturbance doubled its share of the total damage in the last 20 years. Forest disturbances can profoundly impact ecosystem services (e.g., climate change mitigation), affect regional forest resource provisioning and consequently disrupt long-term management planning objectives and timber markets. We conclude that adaptation to changing disturbance regimes must be placed at the core of the European forest management and policy debate. Furthermore, a coherent and homogeneous monitoring system of natural disturbances is urgently needed in Europe, to better observe and respond to the ongoing changes in forest disturbance regimes.

Keywords: European forests; bark beetles; climate change; empirical disturbance data; fire; forest natural disturbances; windstorms.

FIGURE 1

Division of the countries included in this study in ecological zones (ecozones). Map lines delineate study areas and do not necessarily depict accepted national boundaries.

FIGURE 2

Conceptual flow diagram of the gap‐filling exercise.

FIGURE 3

Total reported damage caused by natural disturbance in Europe between 1950 and 2019.

FIGURE 4

Comparison between reported data (grey area) and data gap‐filled using RF models trained on reported only (red solid line) and expert's interpreted time‐series (green dashed line), respectively.

FIGURE 5

Expert's interpreted gap‐filled time‐series of disturbance drivers between 1950 and 2019. The values represent the sum of the 34 European countries object of this study. The bars represent a decadal average. The lines are linear models fitted to the decadal averages. The scales of the panel's y‐axis differ for improving the visualization.

FIGURE 6

Decadal and overall (1950–2019) averages of countries SDIs based on experts' interpreted gap‐filled time‐series. Specific values are reported in supplementary material 5 together with values for the other time‐series.