since root productivity data are not yet available. Moreover, this Wnding does not allow for any conclusion on the occurrence of ‘overyielding’ in terms of bulk above-ground biomass or productivity in these stands. The identity of co-occurring tree species had no signiWcant inXuence on the morphology of the roots; root diameter distribution, tip fre- quency, and speciWc root surface area showed characteristic diVerences among the species, but were more or less similar in monospeciWc and species-rich stands. Thus, the tree spe- cies were rather conservative with regard to the morpholog- ical plasticity of their Wne roots and also the vertical Wne root distribution patterns. This held true although the recorded Wne root biomasses as well as the total root surface areas of the stands indicate rather high Wne root densities that should cause intense below-ground competi- tion. However, it remains open whether species-speciWc diVerences in Wne root lifespan aVect the below-ground productivity of the studied stands.
Acknowledgments This study was funded by the German Research Foundation (DGF) in the context of the Research Training Group 1086 ‘The role of biodiversity for biogeochemical cycles and biotic interac- tions in temperate deciduous forests’. We are very grateful to the National Park administration for the permission to conduct the study in the Hainich National Park. Data of forest stand parameters were kindly provided by Mascha Brauns, Anja Guckland, Andreas Mölder and Inga Schmidt.