Experimental enhancement of forest structural heterogeneity can promote biodiversity in managed Central European forests - A remote sensing perspective

Central European forests are experiencing excess tree mortality since multiple years due to consecutive drought events. Increasing disturbance frequency and intensity have been reported leading to more planned and unplanned changes in forest structure. Novel forest management techniques are required to maintain future forest health by promoting biodiversity and multifunctionality through improved resilience towards disturbance. Enhancing the structural heterogeneity of forests has been identified as a key management technique to benefit biodiversity. We study experimental silvicultural treatments with increased variety of light conditions (selective thinning and gap felling) and deadwood features (downed deadwood, standing deadwood, habitat trees) that have been implemented in Central European broad-leaved forests to enhance forest structural heterogeneity. This unique large-scale forest manipulation experiment (234 patches in six regions of German forests) in the context of the interdisciplinary BETA-FOR project aims to provide novel insights on forest structure-biodiversity relationships with a direct context to forest management practices. In the present study, multi-source remote sensing analyses comprising in-situ (mobile and terrestrial laser scanning) and spaceborne data (Sentinel-1, Sentinel-2 time-series) were conducted to investigate enhanced forest structural heterogeneity in experimental silvicultural treatments. In addition, wall-to-wall forest structure data derived from a machine-learning modeling workflow combining GEDI, Sentinel-1 and Sentinel-2 data was considered for analyses. We found strong correlations (greater than 0.7) among in-situ and spaceborne data on forest structure. This finding demonstrates the potential of spatio-temporal continuous forest structure indicators derived from spaceborne sensors to complement local measurements on forest structure from in-situ platforms. In addition, multi-taxa biodiversity data (taxonomic diversity of bats, birds, gastropods, hoverflies, insects, moths, spiders, tree species) was analyzed to study forest structure-biodiversity relationships. Moderate correlations (greater than 0.4) for taxonomic diversity of birds, gastropods, hoverflies, insects, and tree species to spaceborne indicators of forest structure were identified. Our findings demonstrate the potential of multi-source remote sensing to monitor forest structure and biodiversity. Therefore, our study confirms the applicability of multi-sensor spaceborne forest structure indicators to monitor forest structure dynamics through novel forest management practices enhancing structural heterogeneity.