ForestTemp – Sub-canopy Microclimate Temperatures of European Forests

Ecological research heavily relies on coarse-gridded climate data based on standardized temperature measurements recorded at 2 m height in open landscapes. However, many organisms experience environmental conditions that differ substantially from those captured by these macroclimatic (i.e. free air) temperature grids. In forests, the tree canopy functions as a thermal insulator and buffers sub-canopy microclimatic conditions, thereby affecting biological and ecological processes. To improve the assessment of climatic conditions and climate-change-related impacts on forest-floor biodiversity and functioning, high-resolution temperature grids reflecting forest microclimates are thus urgently needed. Combining more than 1200 time series of in situ near-surface forest temperature with topographical, biological and macroclimatic variables in a machine learning model, we predicted the mean monthly offset between sub-canopy temperature at 15 cm above the surface and free-air temperature over the period 2000–2020 at a spatial resolution of 25 m across Europe. This offset was used to evaluate the difference between microclimate and macroclimate across space and seasons and finally enabled us to calculate mean annual and monthly temperatures for European forest understories. We found that sub-canopy air temperatures differ substantially from free-air temperatures, being on average 2.1°C (standard deviation ± 1.6°C) lower in summer and 2.0°C higher (±0.7°C) in winter across Europe. Additionally, our high-resolution maps expose considerable microclimatic variation within landscapes, not captured by the gridded macroclimatic products. The provided forest sub-canopy temperature maps will enable future research to model below-canopy biological processes and patterns, as well as species distributions more accurately. Academy of Finland 337552 European Research Council 757833 Akademie Ved Ceske Republiky RVO 67985939 Agentura na Podporu Vyskumu a Vyvoja APVV-19-0319 Agency of the Czech Republic GACR 20-28119S University of Helsinki 7510145 Research Foundation Flanders G0H1517N, W001919N Austrian Science Fund 193645, 20FI20_173691, 20FI21_1489 Structure Federative de Recherche Condorcet FR CNRS 3417 KU Leuven 3E190655 French National Research Agency ANR-19-CE32-0005-01 ETH Zurich FEVER ETH-27 19-1