Typology and ecology of Californian serpentine annual grasslands

摘要

A first classification for serpentine annual grasslands distributed throughout northern and central California is proposed. This study has followed the Braun-Blanquet phytosociological system based on floristical, biogeographical and bioclimatic features of the sampled areas. Numerical analyses of classification and ordination were applied to the floristic releves. Minimum Variance Clustering grouped releves into basic classification units that allowed us to define low-hierarchical syntaxonomical units (associations) and 'communities'. A Principal Coordinate Analysis was used to extract those ecological parameter, related to the axes that separate those classification units from the previous dendrogram. The results showed that differences in species composition was mainly due to a continentality gradient and the shady effect of an overstory vegetation. On the basis of both analyses we propose a first syntaxonomic scheme on ultramafic (mainly serpentine) annual plant communities of the biogeographical Californian Region that comprises four associations, two subassociations and some provisional communities.