SPECIES RICHNESS PATTERNS IN THE UNDERSTOREY OF PYRENEAN PINUS-SYLVESTRIS FOREST

Species richness was studied in the understorey of natural Pinus sylvestris forest in the eastern Pyrenees. Understorey plant species were grouped in three structural groups as woody species, herbs and mosses. The response curves of total species richness and species richness of each structural group were fitted against environmental and stand-structural parameters, using Generalized Linear Models. The results suggested that, to predict species richness, environmental parameters were more important than tree-canopy structural parameters, in particular incoming radiation and soil nutrient concentration. The species richness, response curve was often humped in relation to soil nutrient concentration. Different patterns of species richness were found for each structural group.