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

Species richness was studied in the understorey of natural Pinus sylve stris forest in the eastern Pyrenees. Understorey plant species were g rouped 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-stru ctural parameters, using Generalized Linear Models. The results sugges ted that, to predict species richness, environmental parameters were m ore important than tree-canopy structural parameters, in particular in coming radiation and soil nutrient concentration. The species richness , response curve was often humped in relation to soil nutrient concent ration. Different patterns of species richness were found for each str uctural group.