Abstract

Forest microclimates – key regulators of biodiversity and forest functioning – are often substantially buffered from the macroclimate. Variation in microclimates is thus expected to explain some of the uncertainty in predicting forest biodiversity responses to climate change. Here, I use data from a network of microclimate sensors across temperate European forests to show that daily maximum air temperatures during summer are on average cooler by 2.2 °C inside than outside forests, and that canopy cover is a key driver of this temperature buffering. I then use a predictive approach to reconstruct changes in microclimate maximum temperatures in 2900 resurveyed forest plots between 1934 and 2016. The macroclimate and the microclimate warmed at a similar mean rate (0.43 and 0.44 °C 10 yrs-1, respectively) but microclimate warming rates varied much more (-0.88 to 2.17 °C 10 yrs-1) than macroclimate warming rates (-0.24 to 1.09 °C 10 yrs-1). Microclimate warming was related to plant community shifts toward warm-adapted species (thermophilisation), while macroclimate warming was not. Predictions of forest biodiversity responses to climate and land use change thus greatly depend on changes in canopy cover and associated temperature buffering. Together with advanced microclimate mapping techniques based on remote sensing, our work contributes to more reliable assessments of ecosystems responses to global change.