Land ownership affects diversity and abundance of tree microhabitats in deciduous temperate forests

Tree microhabitats - e.g. cavities, bark pockets or crown dead wood - have been described as key habitat elements, which are particularly important for birds, bats and xylobiont insects. They are therefore vital for promoting biodiversity in forest ecosystems. The occurrence of such tree microhabitats in forest stands is closely related to forest management. In Central European cultural landscapes, forest areas are subdivided into a mosaic of stands under different ownership types and owners vary in their forest management strategies and practices. However, little is known about the influence of forest ownership on the density and diversity of tree microhabitats in forest stands. In this study, we investigate tree microhabitats - categorised into 31 different tree microhabitat types - within forest stands in clusters of different ownership types. We compare small-scale private forests, municipal forests and state-owned forests in deciduous temperate forest ecosystems in south-western Germany. Our results reveal that the density of tree microhabitats per hectare is more than twice as high in small-scale private forests than in municipal or state-owned forests. Similarly, the diversity of tree microhabitats related to area is highest in small-scale private forests. Moreover, we found differences in tree microhabitat occurrences under the three ownership types at the single tree level. Besides ownership type, relevant indicators for tree microhabitats are basal area of forest stands as well as tree vitality and diameter. Within the study region, the share of tree microhabitats provided by small-scale private forests plays a substantive role for overall forest biodiversity. Management of publicly owned forests should promote a higher density and diversity of tree microhabitats to comply with goals of close-to-nature forest management approaches. In conclusion, we regard the type of forest ownership as a relevant driver of tree microhabitat occurrence. Ownership should therefore be considered in the design of policy frameworks and instruments which address the promotion of forest biodiversity. (C) 2016 Elsevier B.V. All rights reserved.