The combined role of topography and overstory tree composition in promoting edaphic and floristic variation in a Mediterranean forest.

10 pages, 7 tables, 1 figure, 47 references. Special thanks go to Ana Mouro, Joao Luís Mouro, Miguel Porto, Nuno Pires and Sara Dias for assisting in the fieldwork, and Nuno Gomes and associated workers for the EDM loan and field aid. http://www.irnase.csic.es/users/lventura/ER_20_668.pdfThis study aimed to address which factors, other than topography, contribute to the floristic variation of forested slopes. The natural forest studied is located in the Sudoeste Alentejano e Costa Vicentina Nature Park (southwestern Portugal). We sampled topographic, edaphic, floristic and community structure variables along three bottom–top hillside transects. Multivariate analyses of soil variables (by PCA), and of woody species composition and floristic–environmental relationships (by CCA and pCCA) were performed. Environmental–floristic trends strongly associated with the elevation gradient were identified. At lower altitudes, the lowest species richness, the highest soil fertility, and the tallest and most dense (least available light) canopy occurred. The spatial variation in woody species composition and abundance was closely associated with Zn availability in the soil and litter groundcover, but these varibles had significant spatial structure in the studied forest.This work was financially supported by the SFRH/BD/8322/2002 grant to the first author, given by the Portuguese Technology and Science Foundation (FCT), Ministry of Sciences and High Education; T.M. and L.V.G. were supported by the project HETEROMED (REN2002-4041-C02-02).Peer reviewe