Abstract:

In this paper, we explore altitudinal richness of vascular plant species in the Three Gorges region of the Yangtze River and test several hypotheses concerning geographic diversity patterns. Multivariate regression and variation partitioning analyses were used to examine the relative effects of area, climate, geometric constraints and topographical heterogeneity on altitudinal richness patterns, and also the differences among ecological groups (including species with different range sizes, growth forms and biogeographic affinities). Our results show that, water–energy dynamics have the strongest total effect (>93%) in explaining richness patterns for various species groups. However, for many species groups the effects of water–energy dynamics were largely shared with geometric constraints, topographical heterogeneity or area. Geometric constraints had strong effects on species with large ranges, but negligible effects on small-ranged species. Area showed relative strong correlation with species richness, but was excluded from multivariate models for most species groups, when other potential mechanisms were considered simultaneously. On the contrary, topographic heterogeneity showed weak correlation with richness patterns but was included in most of the final multivariate models. We concluded that water–energy dynamics were most important in explaining altitudinal richness patterns within the study region, while geometric constraints were important for species with large ranges. Topographic heterogeneity showed a weak but essential role in shaping altitudinal richness gradients, while the role of area on richness patterns requires further investigation because of the collinear relationships between area, geometric constraints and climatic gradients.