Increasing influence of the surrounding landscape on saproxylic beetle communities over 10 years succession in dead wood

Abstract

Studies of the spatial scale to which saproxylic beetles respond to the surrounding landscape have generated varied results. We tested how the relationship between beetle fauna and variables describing the landscape changed over ten years of succession. We hypothesized that the relationship to the nearby landscape would be stronger when the wood was in a later successional stage. This is because habitat predictability is higher in the later stages, as they have a longer turnover time of beetle assemblages than early stages. With higher predictability of the habitat, theory expect lower dispersal capacity of hosted species, and thereby higher relation to landscape on smaller scale. The saproxylic beetles were sampled on the same wood objects (high stumps) in three time steps over ten years in 20 clear-cuts in south Sweden. In accordance with our expectations, the nearby (<5 km radius) forest-landscape variables explained more of the species composition of the saproxylic beetles later in the succession. The first- and third-years geographical location (longitude and latitude) were more important and explained, for three different subsets of beetle species, 21%, 4% and 25% of the fauna composition. At this time, the forest-landscape variables explained almost nothing. After ten years the pattern was the opposite, with surrounding forest explaining up to 27% of the variation, and regional factors almost nothing. We showed that this was related to a shift in the species assemblage after ten years, with an increasing share of species associated with more decayed wood. Our results suggest that successional stage of the dead wood helps explain at what scale saproxylic species respond. Several of the surrounding forest variables were associated with biodiversity hotspots, which thus seem to exist also for species associated with abundant wood types. Later-successional species are more indicative of hotspots than earlier-successional species.