Beta diversity of angiosperms in temperate floras of eastern Asia and eastern North America

The diversity of a region reflects both local diversity and the turnover of species (beta diversity) between areas. The angiosperm flora of eastern Asia (EAS) is roughly twice as rich as that of eastern North America (ENA), in spite of similar area and climate. Using province/state-level angiosperm species floras, we calculated beta diversity as the slope of the relationship between the log of species similarity (S ) and either geographic distance or difference in climate. Distance-based beta diversity was 2.6 times greater in the north-south direction in EAS than in ENA and 3.3 times greater in the east-west direction. When ln S was related to distance and climate difference in multiple regressions, both distance and climate PC1 were significant effects in the north-south direction, but only geographic distance had a significant, unique influence in the east-west direction. The general predominance of distance over environment in beta diversity suggests that history and geography have had a strong influence on the regional diversity of these temperate floras.