Post-disturbance treatment effects on microclimate and vegetation recovery on Norway spruce calamity areas from in situ and UAV-based monitoring

Abstract

Microclimate is crucial for forest regeneration, yet its variation under different post-disturbance management strategies remains insufficiently quantified. We investigated microclimate and vegetation recovery over three years, following drought and bark-beetle-related die-back of Norway spruce (Picea abies) in a disturbance hotspot in Central Europe. Using microclimatic and UAV-based monitoring, we evaluated four post-disturbance treatment variants: standing deadwood, high stumps, clearing and mulching. Vegetation cover increased from ∼30 % up to ∼70 % in plots of standing deadwood and mulch. Substantial microclimatic differences emerged among treatments. During the growing season, diurnal amplitudes were largest in cleared and mulched plots (∼23 K), while standing deadwood maintained significantly lower maximum temperatures (∼3 K cooler during heat events) and narrower amplitudes (∼19 K), indicating superior thermal buffering. Frost events were over three times more frequent in open areas than in vital stands and moderate in standing deadwood. Temperature patterns in high stumps (dead trees cut at 2 m height) were similar to cleared and mulched plots, though stem-associated microhabitats require further investigation. Soil moisture was highest in standing deadwood, even exceeding levels of vital stands, and slightly increased with mulching. An increasing wetting trend in the high stump plot could be associated with vegetation development. UAV imagery corroborated in-situ data and revealed considerable spatial heterogeneity in surface temperatures across treatments and surface cover types. These findings underscore the role of structural legacies in buffering microclimatic extremes and supporting regeneration. As heat and drought events intensify, microclimate-sensitive management offers a promising strategy for fostering climate-resilient forests.