Benefit for some, harm for others: Forest structural changes following recent drought years have contrasting effects on bat habitats

Structural changes in Central European forests have recently accelerated, with uncertain impacts on biodiversity. Using remote-sensing data, this study investigates changes in multiple structural attributes of a temperate mountain forest in Germany between 2015 and 2021, a period characterised by two droughts, increased tree mortality, and adaptive management. To evaluate retention measures under these conditions, which aim to provide old-growth structures, structural changes were analysed in relation to retention management and forest ownership type. In addition, changes in habitat suitability (HS) were assessed for nine bat species(-groups). Following drought years, canopy height heterogeneity and forest gaps increased while tree volume decreased, particularly in coniferous forests (-41.7 m 3 /ha). Standing deadwood cover tripled but remained low (0.1 % vs. 0.3 %) and showed a limited persistence. Height heterogeneity remained highest in state forests with retention measures, compared to those without, and to corporate or private forests. Private forests - and in mixed or deciduous forests, also state forests with retention measures - maintained higher average tree volumes. However, forest structure development was broadly similar among ownership and management types, particularly within coniferous forests most affected by drought and adaptive management practices. While open forest structures were previously lacking, recent changes have improved habitats for bats adapted to edge and open environments. In contrast, species adapted to high tree volumes, such as Myotis and Plecotus bats, may experience adverse effects. Thus, maintaining mature forest habitats is becoming increasingly critical, and retention levels should be enhanced and refined to preserve disturbance legacies. • Following drought years, tree volumes declined in coniferous forests. • Standing deadwood cover remained low with a high turnover. • Retention forestry sites maintained heterogeneous canopies, which many bats prefer. • Disturbances and adaptive management reduce structural differences among forests. • Open habitats increased, conserving mature forest-adapted species gains importance.