The relationship between tree species richness, canopy space exploration and productivity in a temperate broad-leaf mixed forest

The relationship between tree species richness and forest productivity is not well understood. We used ground-based laser scanning for analyzing the canopy structure and three-dimensional space filling by foliage and twigs in a species-rich temperate old-growth forest to test the hypotheses that (i) canopy space filling increases with tree species richness, and (ii) a higher degree of canopy space filling in diverse stands is linked to higher aboveground productivity (NPPa). Space filling was quantified in 80 plots with variable species composition (five species) and species richness (1-3 species) and related to stem wood and litter production. Neither space filling nor NPPa were higher in more diverse than monospecific plots, while species identity had a significant effect on the patterns of space occupation in the sun and shade crown. We conclude that increased complementarity in canopy space filling among the species is not an important productivity-determining factor in this temperate mixed forest.