Coverage based diversity estimates of facultative saproxylic species highlight the importance of deadwood for biodiversity

Abstract

How many species can live in a specific habitat is a key question in conservation biology. Due to its heterogeneity, deadwood supports highly diverse communities. The total number of species related to deadwood is, however, underestimated by most empirical community studies. First, as most reports on saproxylic species richness do not relate the number of species observed to the sample size used, it is not possible to draw conclusions about the representativeness of the species richness observed. Secondly, the assessment of species richness is usually limited to obligate saproxylic species, i.e., species classified by experts as being strictly dependent on deadwood. Hence, many species are ignored that can be considered facultative saproxylic; i.e., they are not dependent on deadwood but clearly benefit from it. The present study aims to statistically estimate the proportion of obligate and facultative saproxylic species among Coleoptera, Arachnida and Heteroptera in a European mountain forest. Therefore, we applied rarefaction/extrapolation based on sample coverage estimators, using data from an experimental approach including three trapping methods. The estimates suggest that obligate and facultative saproxylic beetles account for 28% and 19% of the total species richness of beetles, respectively. The estimated proportion of obligate saproxylic Heteroptera and Arachnida species was 4% and 12%. Facultative saproxylics were estimated to account for 24% and 69% of the total species richness, respectively. In summary, our study shows that the share of arthropod diversity related to deadwood is about 50 to 70%, within the three taxa Coleoptera, Arachnida and Heteroptera in a temperate forests temperate mountain forest, which is higher than previously assumed. This highlights the importance of deadwood for forest biodiversity and further supports deadwood restoration activities.