Forest damage from wood- and bark-borers has significantly increased across Europe. Such infestations often result in large-scale tree mortality. Credit: Simon Blaser

Insect-driven tree mortality is rising across Europe, according to an international study led by the Czech University of Life Sciences with participation of WSL. Conifers are hit harder, broadleaf damage declines and warm, dry regions are most affected. These results, published in Global Change Biology, can help forest management by informing species choice and climate adaptation.

Tree-feeding insects are affecting Europe’s forests increasingly but in uneven ways. The international team from 17 European countries, including WSL for Switzerland, reports that wood-boring insects are causing increasing damage to multiple conifer species, while defoliation caused by caterpillars of different moth species has been declining in recent years. Across temperate and boreal Europe, insect disturbance is consistently higher in warmer and drier regions, indicating the risk of large, sudden impacts as climate extremes intensify.

“Our results show a clear signal: conifer-dominated forests are increasingly vulnerable to wood- and bark-boring insects, in particular the spruce bark beetle, while broadleaved tree species are experiencing decreasing levels of damage from a more diverse group of insects,” said Tomáš Hlásny, the study’s lead author from the Czech University of Life Sciences Prague. “These findings are important, providing guidance for forest management, tree species choice, climate change adaptation, and planning of future timber markets.”

Guide for forest management

The findings support policies that shift forest management toward more climate-resilient tree species compositions, with the dominance of broadleaved species, alongside stronger, interoperable monitoring of forest disturbance and data sharing across countries.

“We need adaptation strategies that reflect diverging disturbance trends and uneven exposure levels across Europe’s forests,” Hlásny said. “This requires effort in coordinated forest risk monitoring, harmonized data collection and sharing, and guidance that can be acted upon by managers and inform markets.”

Researchers compiled annual disturbance records from 15 European countries for more than two decades (2000–2022), including data from Swiss Forest Protection and the Swiss National Forest Inventory, which is led by the WSL. The dataset represents 1,361 time series for 50 insect species.

The team analyzed trends by feeding guild (borers vs. defoliators), host tree species group (conifers vs. broadleaves), and geographic/climatic gradients. The work also introduced a novel harmonized disturbance dataset designed to complement existing monitoring and support future research.

More information: Tomáš Hlásny et al, Divergent Trends in Insect Disturbance Across Europe’s Temperate and Boreal Forests, Global Change Biology (2025). DOI: 10.1111/gcb.70580

Citation: Tree mortality from insects is rising across Europe (2025, November 3) retrieved 3 November 2025 from https://phys.org/news/2025-11-tree-mortality-insects-europe.html

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