Effects of retention forestry on bats: relations between forest structure and the landscape matrix

Abstract

With more than 1200 species worldwide and comprising roughly one fifth of all mammalian species bats are of great importance for global biodiversity. As bio-indicatorsa they are frequently selected target species for conservation programmes. Most species depend on forests for at least part of the year: forest gaps are used as foraging sites, old and dead trees as roosting locations. However - in spite of the expanding forest area in Europe - only a small proportion thereof is set aside for nature conservation purposes. The vast majority is primarily managed for wood production, which leads to a simplified forest structure, lacking gaps, dead wood and senescent trees. Retention programmes, integrating old-growth structures in a managed forest matrix are thus considered beneficial for the promotion of forest biodiversity, but their effectiveness for bats may strongly depend on the landscape context and targeted species. Whereas species-specific associations of bat occurrence with forest structures has been shown on a local scale, minimum landscape-scale requirements for abundance and distribution of such structural elements are lacking.

In this study, embedded in a transdisciplinary research programme examining the effectiveness of retention forestry for biodiversity in temperate forests, we relate bat diversity, activity, and type of use to forest characteristics and landscape heterogeneity. We expect that: (1) The species-specific use of structural elements at the local scale will be modulated by the surrounding landscape. (2) The diversity of species and functional guilds will increase with heterogeneity at both the forest stand and landscape scale. (3) The relative abundance and diversity of forest-specialists will increase with the abundance of old forest (habitat trees) and standing dead wood in the surroundings.

Bat species were recorded using non-invasive bioacoustic methods (ultrasonic sound recording) at 135 study plots of 1ha, distributed across the Southern Black Forest, Germany. Forest structure and landscape patterns were assessed within a 25km2 buffer by remote sensing complemented with plot-scale terrestrial mapping. LiDAR-information capturing the 3D-characteristics of sub-canopy space was used to predict bat occurrence at the stand scale. Here we will present the first results on how retention forestry promotes bat diversity, which species benefit from retention measures and how this effectiveness depends on the surrounding landscape. By relating bat presence and diversity to structural characteristics quantitative threshold values for integrative forest management will be derived.