Species richness of saproxylic beetles in woodlands is affected by dispersion ability of species, age and stand size

Abstract

This study examines the occurrence of saproxylic beetles in woodlands of different size and age and their potential to leave woodland areas and cross open grassland in northern Germany. The beetles were recorded by emergence traps and flight-intercept-traps. The investigated sites were dominated by beech, oak and alder, but other tree species also occurred in low abundance. Species richness showed a positive relation to stand size and age of woods. Both total and rarefaction species richness were the lowest in small and young woods and highest in old and large woods. Species richness decreased asymptotically from the inner-wood habitat to a distance greater than 80 m from the wood margin. 80 species were classified into 46 low mobile species found at a distance 30 m from wood margins. The most mobile species were found the most frequently in all woods; but they contributed less to species richness in wood stands than did the species with low mobility. The contribution of the least mobile species to species richness in wood stands increased with the age and size of the stands, with the effect of stand size being the greater. We conclude that in our study region woods larger than 100 ha are necessary to maintain the highest richness of the least mobile saproxylic beetles.