MODELING FLORISTIC SPECIES RICHNESS ON A REGIONAL-SCALE - A CASE-STUDY IN SWITZERLAND

In this paper a multivariate linear regression model is proposed for p redicting and mapping regional species richness in areas below the tim berline according to environmental variables. The data used in setting up the model were derived from a floristic inventory. Using a stepwis e regression technique, five environmental variables were found to exp lain 48.9% of the variability in the total number of plant species: na mely temperature range, proximity to a big river or lake, threshold of minimum annual precipitation, amount of calcareous rock outcrops and number of soil types. A considerable part of the unexplained variabili ty is thought to have been influenced by variations in the quality of the botanical inventory. These results show the importance of systemat ic floristic sampling in addition to conventional inventories when usi ng floristic data as a basis in nature conservation. Nevertheless it i s still possible to interpret the resulting diversity patterns ecologi cally. Regional species richness in Switzerland appears to be a functi on of: (i) environmental heterogeneity; (ii) threshold values of minim um precipitation; and (iii) presence of calcareous rock outcrops. Acco rding to similar studies, environmental heterogeneity was the stronges t determinant of total species richness. In contrast to some studies, high productivity decreased the number of species. Furthermore, the im plications of this work for climate change scenarios are discussed.