Diversity of the Grass Layer of Urbanized Communities Dominated by Invasive Acer negundo

Abstract

The α-diversity of the grass layer was compared for communities exposed to Acer negundo and unexposed communities. The communities were aligned by characteristics by their degrees of urbanization, fragmentation, and anthropogenic disturbance. The research was carried out in the city of Yekaterinburg (the southern taiga subzone, Russia) at 13 sites. Each site included two sampling plots: one in communities dominated by A. negundo and the other in communities dominated by other tree species (total of 26 communities). It is established that the key factors of variation in the grass layer characteristics are the dominant tree species (A. negundo or other trees) and the stand area. The number of grass species per 400 m² was lower in A. negundo thickets than under the crowns of other trees: 17 ± 3 and 28 ± 3, respectively. However, communities with and without A. negundo did not differ in the values of the Shannon index, the degree of dominance, or the ratios of annual/perennial and graminoid/forb species. An increase in the degree of habitat fragmentation was accompanied by an increase in the proportion of synanthropic species, both under the canopy of A. negundo and in communities dominated by other trees. Methodically, the results showed that assessment of the consequences of plant invasion should always take into account the spatial patterns of determination of the structure of communities.