An Approach to the Identification of Indicators for Forest Biodiversity—The Solling Mountains (NW Germany) as an Example

In this study, we present an approach for the identification of indicators for biodiversity within forest ecosystems. We analyze the data of stands of pure Norway spruce (Picea abies (L.) Karst) and European beech (Fagus sylvatica L.), as well as mixed P. abies–F. sylvatica forests in the Solling mountains (NW Germany). The analysis is based on 683 vegetation samples in total. For different plant groups, that is, vascular plants, bryophytes, Red List species, we investigate species numbers as a parameter of biodiversity. Species numbers are differentiated into three classes to describe low to high diversity. Plots are separately examined for the three different forest types. In order to take the species–area relationship into account, we only use releves with a plot size of 100 m2. Our approach focuses on the probability to be in a defined range of species numbers, that is, class, if a certain species occurs. For the purpose of facilitating the differentiation of the classes, we use the presence values of species in the classes for further characterization of indicators. Few indicators were found for the low ranges of species numbers. In addition, there were only a small number of species groups and stand types having indicators for all three classes. Various species have multiple indicator functions, e.g., with regard to the investigated species groups. The focus on a few of these multi-indicators allows a rapid assessment of forest biodiversity. The catalog of indicators resulting from the investigation helps to facilitate and accelerate biodiversity evaluations of forest stands, in particular with regard to nature conservation and the restoration of natural forests.