Bridging spatial scales: UAV laser-scanning to identify high quality habitats for a highly endangered forest butterfly

The destruction of natural and semi-natural habitats and the reduction of habitat quality leads to the loss of biodiversity. Heterogeneous forest ecosystems provide valuable habitats for many plant and animal species. Intensification in forestry caused the severe decline of such light deciduous forests across major parts of Central Europe. This negatively impacts many forest species. The Scarce fritillary butterfly Euyphydryas maturna requires specific resources and habitat structures during the adult and larval stage. Thus, the microhabitat level as well as forest landscape scale is of relevance. In this study, we bridge spatial scales and analyse habitat requirements of this highly endangered forest butterfly using UAV-based laser-scanning and field observations, including micro-habitat parameters and microclimatic conditions across a forest section in Northern Austria. For this purpose, we mapped all growing ash trees, the main larval food plant of E. maturna across our study area. We recorded the occupancy of the ash trees by the butterfly species. We assessed micro-habitat structures and microclimatic conditions around each ash tree and across the entire forest from the air, using a LiDAR system. We found that the majority of ash trees in our study area are of low vitality, and there are hardly any mature ash trees left. Most larvae could be found in the south to southeast orientation of a tree, and at an elevation between 2 and 3 m. LiDAR-data showed that egg oviposition took place preferably on vital trees, which are surrounded by other high trees in the north. Warm and moist microclimate, as well as the availability of further host plants such as herbs and shrubs around ash trees drive the habitat preference for this butterfly species. This study and the results highlight the importance of combining both, whole ecosystem structure with high-resolution data and microhabitat information to understand species ecology and the conservation of sensitive habitats.