Unterwuchs als wichtige Habitatqualität für xylobionte Käfer im Buchenwald
Abstract

In three differently structured beech habitats, beetles as well as their accompanying fauna were sampled by means of pit fall traps and photo eclectors. The interest focused on xylobiontic species. The three sampling sites with identical deadwood supply were situated in the Sauerland (NRW) Germany. The three explored areas represent common production forests with low deadwood portions, merely differed in their ground level habitat structures: exclusively beech underbrush, miscellaneous underbrush, or no underbrush at all. Microclimatic data were collected at the sampling sites, and temperature and humidity were measured in deadwood samples under natural and laboratory conditions.

Between 1993 and 1995 444 beetle species were collected. The area with miscellaneous underbrush featured the highest species diversity (325 species), followed by the site with beech underbrush (290 species). Species diversity was lowest at the location without underbrush (233 species). The same tendencies are displayed by rarefaction calculations, based on identical numbers of individuals percount.

Underbrush has an effect on the microclimate, especially close to the ground, where relative atmospheric humidity remains higher for a longer time, and therefore rather strongly influences climatic conditions in the deadwood. This is reflected by the selective occurrance of species with specific needs regarding humidity conditions or dead wood composition. Both areas featuring underbrush (miscellaneous and beech) show largely corresponding species compositions and comparably well-balanced abundance distributions. The results clarify that not only the mere presence of underbrush influences beetle species composition but its diversity as well. Particularly floricole beetles benefit from a floristically diverse understory. Underbrush diversity is positively correlated with species numbers of beetles, because many of the xylobiont species require not only dead wood, but also lowers for their development.

Moreover underbrush shifts the species composition towards higher predator-prey ratios, thereby potentially reducing the risk, for outbreaks of economically important xylophagus beetles.

The data support the notion, that sustainable forestry supports nature protection and species conservation without endangering wood harvest by forest pests, as long as enough dead wood is available and a diverse underbrush is provided.

The composition of the additional fauna confirms the conclusion derived from the coleopteran analysis: underbrush, especially miscellaneously composed and structured underbrush, provides habitat for a high faunal diversity.