Interactive Effects of Weather and Forest Structure on Microclimate Buffering in European Deciduous Forests

The microclimate temperature within forests can substantially deviate from measurements outside forests. Yet, the amount and direction of this buffering strongly depend on meteorological conditions outside forests, such as free-air temperature, wind speed, soil moisture, precipitation and solar radiation. Most studies on microclimate buffering focus on long-term averages at coarse temporal resolution (e.g., monthly to seasonal), potentially overlooking the impact of daily fluctuations, which are nonetheless critical for many forest species and processes. Here, we linked in situ measured air and soil temperatures, at the daily resolution over a period of more than 5 years across 45 European deciduous forests spanning a 2300-km latitudinal gradient, to daily variation in weather conditions (i.e., free-air temperature, precipitation, wind speed, soil moisture, solar radiation, day length and snow cover). We assessed the interactive effects of weather conditions and forest structural complexity (plant area index) and distance to the forest edge on air and soil temperature offsets. Temperature offsets are the difference between understory air or soil temperature and macroclimate reference conditions measured at weather stations in the open field. We show that relative effect sizes of free-air temperature prevailed over the effects of other weather variables to determine air and soil temperature buffering. In general, higher free-air temperatures, soil moisture, wind speed and snow cover led to more negative air and soil temperature offsets, with variations depending on forest structural complexity and season. Conversely, slightly increased air and soil temperature offsets were found as precipitation and solar radiation increased. Our study highlights the dominant role of daily free-air temperature fluctuations outside forests in shaping microclimatic buffering. We emphasize complex interaction paths between daily weather conditions, and forest structure and edge effects, offering valuable insights for next-generation microclimate models and enhancing our understanding of forest ecosystem responses to environmental change that account for microclimate.