Comparative Analysis of the Species Richness of Life Forms of Vascular Plants in the Middle Volga

Abstract

A single quantitative index d has been introduced for the spectrum of seven life forms (LFs) characterizing the proportions of their species richness (SR) in the Middle Volga region at 25 sites 100 km² in size each. It is established that d grows with moisture provision. All significant relationships between the SR of different LFs are positive. However, a different sign is identified between the fractions of the number of species of each LF of the total number of species or the relative species richness (RSR). For example, a close negative relationship was found between the RSR of LFs dominating in the region, hemicryptophytes and annual herbs (therophytes). Using the regression models, the specificity of links for the SR and RSR of seven LFs with climate and topography is shown. It was established that precipitation is more important for some LFs in the region and temperature is more important for others. The links are closer when taking into account the slope insolation, but the signs of links between it and the SR of different LFs may be different. According to regression models, SR and RSR maps of hemicryptophytes and therophytes are calculated. The maps show the separation of these LFs in space: the location of hemicryptotes to flat water divide areas and therophytes to the northeastern slopes. In the region under study, the main environmental factors differentiating these LFs in space are the energy of solar radiation and the precipitation of March and winter. This separation of LFs po-tentially leads to reduced competition between them.