Abundant and rare spiders on tree trunks in German forests (Arachnida, Araneae)

Theo Blick

doi:10.5431/aramit4002

Abstract

The spider fauna active on the bark of trees in forests on eight sites in different regions in Germany was investigated. Trunk eclectors at about 2-4 meters height on living trees were used in different regions of Germany (SW Bavaria, Hesse, Brandenburg) between 1990 and 2003. In Hesse eclectors were also used on dead beech trees (standing and lying). In this study data, mainly from beech (Fagus sylvatica) and spruce (Picea abies), from May to Octo- ber are compared - whole year samples (including winter) are only available from Hesse. A total of 334 spider species were recorded with these bark traps, i.e. about one third of the spider species known from Germany. On average, each of the eight regions yielded 140.5 (± 26.2) species, each single tree 40.5 (± 12.2) species and 502 (± 452) adult spiders per season (i.e. May to Oct.). The 20 most abundant species are listed and characterised in detail. Six of the 20 species were not known to be abundant on bark, three prefer conifers and three beech/broadleaf. Even in winter (December-March) there was a remarkably high activity on the trunks. However, only a few spe- cies occur exclusively or mainly in winter. Finally, the rarity of some bark spider species is discussed and details (all known records in Germany, phenology) of four of them are presented (Clubiona leucaspis, Gongylidiellum edentatum, Kratochviliella bicapitata, Oreonetides quadridentatus). The diversity and importance of the spider fauna on bark in Central Europe is still underestimated.

Highlights

The spider fauna of tree trunks in Germany and Central Europe is much less well known than the epigeal fauna active on the forest floor
In Central European forests knowledge about the tree trunk fauna reaches an estimated maximum level of 5% compared with the epigeal fauna
Trunk eclectors (Fig. 1, method after BEHRE 1989, see BRAUN 1992, DOROW et al 1992, ENGEL 1999) at heights from 2 to 4 meters on living trees were used in different regions of Germany (SW Bavaria, Hesse, Brandenburg) (Fig. 2)

Summary

Introduction

The spider fauna of tree trunks in Germany and Central Europe is much less well known than the epigeal fauna active on the forest floor. The epigeal spider fauna of common forest types – at least in Central Europe – is significantly less intensively investigated than that of the epigeal fauna of special habitats, such as those that are extremely dry or wet (HÄNGGI et al 1995). I estimate that this disproportion is much higher, if one compares the epigeal spider fauna in forests with the tree trunk spider fauna. In Central European forests knowledge about the tree trunk fauna reaches an estimated maximum level of 5% compared with the epigeal fauna. In each of the four Strict Forest Reserves investigated until now 162 to 202 spider species were recorded (BLICK 2009). As the complete spider coenoses and species lists were already published (see below) or will be published elsewhere, the focus here is on the following topics: (a) totals of species and abundances, (b) the 20 most abundant spider species, (c) winter activity, and (d) notes on rarely or very rarely recorded species

Methods

Results

Conclusion