100 diversity clusters

While the plot-approach aims to quantify the effect of tree-species diversity on biogeochemical cycles on the level of stands, the cluster approach aims to identify causal relationships for these findings. Are the differences between stands of contrasting tree species diversity a consequence of the species being present in the stands? Or do we observe true effects of species numbers that are independent of species identity? Which interactions between species contribute to true biodiversity effects?

Interaction mechanisms between species are studied in tree groups, so called clusters, which consist of 3 co-dominant trees and their direct neighbours. On the one hand, we measure balance quantities in order to quantify long-term effects of the given neighbourhood combination. On the other hand, we describe relationships between tree characteristics, facilitation- and competition-processes and flow rates with high spatial resolution and analyse them with process-oriented models.

In order to distinguish biodiversity effects from species-identity effects, all possible combinations of 3 trees out of the 5 analyzed tree species were realized in clusters. We have 4 replicates for each combination. Due to the samll-scale mosaic of tree-species in Hainich National Park, we were able to establish all 100 clusters in close vicinity to the plots of phase I.