Temporal changes in the beetle and spider communities in a Hessian (German) strict forest reserve

Abstract

In the context of the Hessian strict forest program, the reserve Hasenblick was set aside from forest management in 1988. The program aims to document the faunas of forest reserves in unprecedented detail, using a set of many different sampling methods. Here data on ground dwelling spiders and beetles that were sampled with pitfall traps in 2000 and 2001 and again in 2012 and 2013 are analyzed to assess temporal changes. In light of putative insect declines, we hypothesized a significant decrease in abundance, biomass, diversity, and trait composition of the arthropod communities. No substantial changes in community trait composition were observed in any species group. Abundance, biomass, and functional diversity of beetles and spiders were higher in the second survey, with exception of the beetle biomass, when Anoplotrupes stercorosus was excluded, and the functional diversity of spiders showed only a tendency to be higher in the second survey. Additionally, the extrapolated number of ground dwelling beetle species was higher during the second survey. However, in all tested measures, the observed differences between the surveys were not significantly higher than differences observed between consecutive years. Therefore, we are not able to detect directed long-term trends of (functional) diversity or biomass in our dataset. The results rather indicate high stability of the arthropod communities in this naturally developing forest, although short-term fluctuations in populations are high. And while climatic factors affected abundance and biomass of beetles and spiders overall, the timespan of about 10 years may be too short to clearly detect effects of climate change or changes in forest structure on the trait composition of the beetle or spider communities.