Forests on a solar timer: bark beetle outbreaks follow the sun’s cycle

Forests across Central Europe are facing mounting pressure from climate-induced bark beetle outbreaks. These outbreaks have not only led to the loss of millions of trees but also significant economic losses due to reduced timber quality and increased salvage logging costs. The impacts of forestry disasters and calamities therefore have a significant social impact.

To understand the underlying causes, a research team from the Czech University of Life Sciences analyzed forestry records from 1974 to 2022 across Austria, Czechia, and Slovakia. By comparing logging data with solar irradiance, temperature, precipitation, and atmospheric patterns, the study found that bark beetle-induced logging often follows a distinct 9 to 12-year cycle, closely aligned with solar activity. Specifically, periods of low solar activity, known as solar minimums, are associated with higher incidences of bark beetle outbreaks. Conversely, higher solar activity, measured by total solar irradiance (TSI), reduces the likelihood of these outbreaks.

The North Atlantic Oscillation (NAO) also significantly impact weather patterns. Negative NAO phases (cooler, drier conditions) exacerbate beetle outbreaks, while positive phases (wetter weather) may reduce infestations but increase wind/snow damage.

Dr. Václav Šimůnek, the corresponding author, pointed out, "This suggests that forest management strategies should consider the influence of solar cycles and climate patterns. Better awareness of these patterns could help forestry officials prepare in advance by clearing storm-damaged trees early or adjusting planting and harvesting strategies ahead of high-risk periods."

Although the study shows a potential relationship between major outbreaks in Central Europe and solar activity, the researchers caution that local conditions and climate change could still intensify or disrupt these patterns. To gain a deeper understanding of this phenomenon, further research is necessary.

This study received financial support from the Ministry of Agriculture of the Czech Republic through Project No. QK21010198, named Adaptation of forestry for sustainable use of natural resources. M.Š. was supported by the project RVO:67985815. This study was supported by the Czech University of Life Sciences Prague, Faculty of Forestry and Wood Sciences (Excellent Output 2025).