Impacts of Microclimatic Processes on foRest bIodiversity redistributioN under macroclimaTe warming – IMPRINT

Species distribution models (SDMs), the toolbox to project biodiversity redistribution under anthropogenic climate change, are based on ambiant-air temperature (i.e. macroclimate) but fail to capture apparent temperature near the ground (i.e. microclimate). Yet, microclimate matters for the distribution of many organisms, especially in the understory of forest ecosystems where management practices will have a prominent role in mediating the processes underlying microclimate. Very recent progress has been made to interpolate microclimate at very fine spatial resolution by combining in-situ microclimate measurements with fine-grained environmental variables derived from remotely sensed images such as light detection and ranging (LiDAR) images. However, these fine-grained spatial interpolations are not dynamic over time and unlikely to reflect the long-term dynamic of climate but rather the weather conditions that prevailed during the year the microclimatic data where recorded. This stems from a lack of long-term monitoring of microclimatic conditions. To lift this technical barrier, we propose a combined use of (i) in-situ microclimate measurements (both temperature and humidity near the ground), (ii) high-resolution LiDAR images and (iii) long-term synoptic records from a national network of permanent weather stations. IMPRINT will rely on this unique combination to not only assess and model the processes underlying microclimate across large spatial extents and at fine spatiotemporal resolution but most importantly to provide a unique opportunity to reconstruct past microclimatic changes and thus assess the magnitude of climate warming in the understory of forest ecosystems. The chief objective of IMPRINT is to use this long-term reconstruction of sub-canopy microclimatic changes into SDMs and show how it affects the projections of forest biodiversity redistribution compared with SDMs relying on macroclimate only, the current state-of-the-art. We assume that relying on microclimatic conditions will not only offset the species' thermal responses perceived by actual SDMs based on macroclimate but it will also delay the projected redistribution under macroclimate warming due to the decoupling between sub-canopy and free-air temperatures (a +1°C increase in free-air temperature corresponds to >1°C increase in sub-canopy temperature over the same period). To test these two hypotheses, we will focus on vascular plants and ground-dwelling arthropods of temperate deciduous forests, two different taxonomic groups providing important ecosystem services in lowland agro-ecosystems inhabited by humans. The main novelty of this project lies in the fact that we will not directly interpolate the spatiotemporal distribution of microclimate as most modelers have done so far, but we will rather interpolate, and eventually extrapolate, it indirectly by first modeling the spatiotemporal dynamic of the processes linking macroclimate to microclimate and then running a transfer function based on these processes to reconstruct past microclimatic changes. The benefit of the proposed project is that it will provide basic forest management strategies to act on microclimatic conditions and thus mitigate the potential negative impact of climate change on forest biodiversity.