Taxonomic differentiation and functional homogenization of flora in the middle part of European Russia as a result of naturalization of alien species

Abstract

Biological invasions triggered by human activity cause large-scale changes in the distribution of organisms, one of the consequences of which is biotic homogenization, revealed in varying ratios for different biotic groups. So far, there are not so many studies assessing the extent of this phenomenon for large areas. For the regions of the middle part of European Russia (ER), changes in the taxonomic and functional diversity of regional flora were analyzed, taking into account naturalized alien species. The Bray–Curtis index was used to quantify the changes in both taxonomic and functional dissimilarity in flora. As a measure of homogenization/ differentiation, we used the difference in similarity indices calculated for regional floras with the participation of naturalized species and only for indigenous ones. The functional diversity of flora is assessed by the type of species belonging to groups of life forms. Naturalized species increase the taxonomic diversity and differences of regional floras, which can be explained by differentiated naturalization depending on the climate. The differentiating effect weakens with increasing distance between the regions. However, an increase in the taxonomic difference of flora is accompanied by functional homogenization, which consists in increasing the proportions of annual/biennial and woody species and reducing the proportion of herbaceous perennials. Changes in taxonomic and functional similarities are interrelated, but proceed at different rates as a result of differences in the leading factors explaining the changes in these categories. Taxonomic diversity is determined by climate to a greater extent than functional diversity, while the ratio of life forms in the structure of flora is mainly associated with the diversity of habitats. Among the groups of biomorphs, annual/biennial species have the greatest homogenizing effect, and an increase in their share contributes not only to functional, but also to taxonomic homogenization.