Undisturbed forest canopies slow understory warming by one-third across Europe

Forests play a critical role in regulating climate change impacts by buffering climate extremes below the canopy. Whether sub-canopy microclimate temperatures warm at a different rate than macroclimate temperatures (in open reference situations) remains, however, an unresolved question. Here, we empirically quantified the magnitude of thermal decoupling between macroclimate and microclimate warming across European forests at high spatial resolution. Using a spatially-explicit machine learning framework that integrates 4,376 in situ summer temperature time series with historical canopy cover dynamics, we reconstructed four decades (1984–2023) of forest microclimate warming across Europe. We reveal that sub-canopy summer temperatures (0.32°C/decade) are warming at a rate approximately 37% slower than macroclimate temperature (0.51°C/decade). However, forest disturbances can abruptly cancel-out thermal decoupling, exposing understories to conditions equivalent to over two decades of additional macroclimate warming. Our findings highlight that thermal decoupling is a key mechanism through which intact forests moderate climate warming, while disturbances can abruptly erase this effect, underscoring the need to explicitly consider thermal decoupling in climate change impact assessments on forest biodiversity and functioning.