Dependence of diversity of floras on climate in the Middle Volga region

Links with climate of richness of species (Ns), genera (Ng) and families (Nf) for 28 polygons each 400 km2 in Middle Volga were studied. Negative correlations with temperatures T and positive with precipitation P of the warm period were revealed, and T and P most strongly affected diversity. Closest links with climate were for Nf, and the least for Ns. We estimated gradients of T and P in four geographic directions. The most pronounced are northern cold-humid and southeastern thermo-arid trends. The northern trend is characterized by a decrease in T by 0.34°C and an increase in P by 17 mm per 100 km; southeast- with an increase in T by 0.27°C and a decrease in P by 15 mm. The cold-humid trend provides the most favorable conditions for the growth of diversity in the region. In it, Ns increased by 36, Ng-by 17, Nf-by 6 per 100 km. For floras with highest Nf and Ng, closer links with T, P and directions are revealed; in contrast to Ns. This indicates the ecological plasticity of the diversity, with different responses to climate variations for different taxonomic levels, which contribute to the preservation of diversity in a heterogeneous climate.