Greiser et al. (2025) Bark beetles as microclimate engineers – thermal characteristics of infested spruce trees at the canopy surface and below the canopy - Data and code

Along a gradient of attack severity, represented by increasing proportions of dead spruces, maximum summer day-time temperatures increased by up to 2 °C, with this warming effect being moderated by the presence of deciduous broadleaf trees. Surprisingly, night-time minimum temperatures were not affected by bark beetle attacks. Secondly, we mapped canopy surface temperature over one part of the study area using multispectral and thermal drone imaging, contrasting canopy temperatures of healthy and infested trees.

We observed that dead trees were generally warmer than living trees, by an average of 2.6 °C on a sunny day and 0.7 °C on a cloudy day. Our study documented changes in thermal regimes in both the understory and overstory after bark beetle attacks, indicating that climate-change related disturbances are fueling rapid increases in microclimate warming. However, even dead forest stands may function as thermal buffers for understory vegetation, as we found minimum temperatures being unaffected by bark beetles.

Finally, our results suggest that increasing the proportion of deciduous trees can decrease the risk of bark-beetle induced microclimate warming. The insights gained can guide forest succession and regeneration management after disturbances, contributing to critical decisions on conservation areas and salvage logging strategies.