The ordination topology based on phylogenetic relatedness, which does not depend on the species identities (Lozupone et al., 2011), also resulted in clustering of regional localities. At the continental scale (1000e10,000 km) phylogenetic clustering of regional samples is believed to reflect biogeographic, rather than ecological processes in community assembly, and common evolutionary history of the regional communities (Webb et al., 2002). It may be argued that community phylogenetic structure is in general less sensitive to environmental filtering than species composition (Lozupone et al., 2011), suggesting that the observed regional community clustering may result from long-distance dispersal limitation. However, our analysis does not fully distinguish between dispersal limitation and environmental filtering, and it is likely that both mechanisms act in tandem