Modelling leaf dispersal and nutrient return in tree species mixtures

Litter fall and the associated nutrient return are a significant supply of resources in forest ecosystems. In mixed stands both litter quantity and quality can change under different species compositions. Spatial heterogeneity inherent in mixed stands, defined by stand structure and the present species, will affect the litter composition around a tree of interest. Therefore spatially explicit information will be needed to determine how neighbour. hood characteristics in a mixed stand have an effect on litter composition and nutrient return. Using a leaf dispersal model, we determined litter production and leaf shedding parameters of four different tree species. Results from this model indicated that the proportion of litter that originated from the neighbourhood was 86% and 77% at the local tree level for oak and beech respectively. Using this information we found that the presence of accompanying species birch or hornbeam had beneficial effects on local return of N, P, Ca, Mg and Mn. Return of K was optimal with only beech trees in the neighbourhood. These results could give an indication on how to use stand establishment, structure and management to optimize nutrient return.