Human intervention often alters the availability of habitat for biodiversity. The conservation of biodiversity therefore requires an optimized habitat management. In forests, dead wood represents one of the most important habitats and in boreal and temperate regions around 25% of forest species depend on it (= saproxylic species). Increasing the amount of dead wood in managed forests has thus become a policy objective, but there is no consensus on how to best distribute dead wood in space. In a landscape experiment, we exposed freshly cut beech branches in bundles of different sizes (one, three, six and 12 branches) in the forest, representing newly created habitat patches to be colonized by saproxylic beetles. We investigated how species richness in a ‘single large’ branch bundle compares to that in ‘several small’ bundles (SLOSS debate). We further tested the effects of dead wood availability (amount and isolation) in the surrounding landscape (20–200 m) and environmental factors (temperature and light availability) on species richness, abundance and community composition.
The species richness of the pooled small bundles (1 + 3 + 6 = 10 branches) was as high as that of the large bundle (12 branches), despite having a smaller total surface, demonstrating the benefit of spatially dispersed habitat patches for total diversity. Also community composition differed and every bundle size yielded some unique species. Dead wood availability in the surrounding landscape had a minor effect in comparison. Our results further highlight the importance of microsite heterogeneity: species richness was related to light availability, and abundance and community composition were related to temperature. Synthesis and applications: Larger amounts of dead wood harbour more saproxylic beetle species and the distribution of dead wood in patches of different sizes within the forest can promote the development of variable species communities. Combined, this results in a higher species diversity. In managed forests, where retained dead wood is often homogeneous in terms of size or tree species, increasing heterogeneity by distributing dead wood in the forest could foster higher diversity of saproxylic species. Keywords: biodiversity, colonization, conservation, dead wood availability, forest management, habitat
heterogeneity, saproxylic beetles, SLOSS
