Indicator species and the management of temperate forests

Background/Question/Methods

Assessing the effects of particular management or conservation measures on biodiversity requires suitable methodology in assessing organismic diversity. With respect to arthropods, an ideal biodiversity assessment would involve all species, which is an unrealistic aim. Several methods of identifying ‘indicators’ for total biodiversity have been proposed but it is still unclear how useful these approaches are. We used the recently developed methodology by Dufrene & Legendre (1997) for the calculation of indicator species to study the effect of land use on biodiversity in 150 temperate forest stands of various management types in three regions of Germany. Our main focus habitat were beech forests including unmanaged and differently managed beech forests but we also considered conifer age-class forests and mixed forest. We asked the following questions:  (1) Can indicator species be derived for unmanaged beech forests and other forest management types? (2) What are the differences between trapping methods and taxon with respect to the incidence of indicator species? (3) Are all indicator species region-specific or are there indicators species that can be used in all of Germany? and (4) what are the traits of the indicator species?

Results/Conclusions

Our analysis shows that there is an surprising number of species that could act as indicator species for particular forest types. While indicator species tended to be among the more abundant species in the study, their abundances differed widely and also included rare species. The number of indicator species in a stand correlated well with overall biodiversity.Indicator species were found are among all the taxa investigated (Opiliones, Neuroptera, Araneae and Heteroptera) and included all trophic levels. The percentage of indicators within trophic guilds differed among regions and forest-types. Only a few species were found to be indicators for a particular forest type in all regions. We argue that the search for indicator species in forests should be data-driven rather than based on a-priori judgements, and should include abundant and inconspicuous, not just rare and eye-catching species. The regional differences in the identity of the indicator species points to limits in using applying the indicator appraoch over large geographical regions.