The effects of edge-interior and understorey-canopy gradients on the distribution of saproxylic beetles in a temperate lowland forest

Spatial distribution of arthropods in woodlands has crucial implications for biodiversity conservation and forest management. However, its determinants are insufficiently known. In particular, studies on arthropod vertical distribution in temperate woodlands report contrasting patterns that are difficult to explain in the current theoretical framework. Using flight intercept traps, we investigated vertical and horizontal distribution and diversity of saproxylic beetles in the understorey and the upper canopy at the edge and in the interior of a temperate, closed-canopy, deciduous forest in South-Eastern Czech Republic. At the forest edge, number of species was >60% higher than in the interior. Preference for forest edge were better pronounced in the understorey than in the canopy. Although number of species did not differed between the forest strata, vertical distribution of individual species as well as the whole assemblages differed between edge and interior. In the forest interior, most (∼80%) species exhibited higher preference for the canopy than at its edge. Multivariate analysis indicated that beetle distribution was affected by variables related to habitat openness and light availability. The results suggest that: (i) Vertical stratification of arthropod assemblages and individual species is context-dependent and variable even within a single forest patch. (ii) Vertical and horizontal distribution of arthropods is driven mainly by sunlight availability and habitat openness. (iii) In the closed canopy forest, the horizontal edge-interior gradient affects distribution of saproxylic beetles more than the vertical understorey-canopy gradient.