Impact of Solidago canadensis L. on Species Diversity of Plant Communities at Different Spatial Scale

It is known that invasive dominants can significantly limit the species diversity of plant communities in microplots. However, it remains unclear whether they are capable of influencing the species diversity of large areas of vegetation. We considered this issue by the example of six areas of plant communities dominated by Solidago сanadensis located in habitats of different types (Belaya River valley, Western Caucasus, 190–210 m above sea level). Within each of them, biomass samples were taken from 25 plots of 0.25 m2, which were then disassembled by species and weighed. The results of the data analysis showed that (1) S. сanadensis significantly reduces the number of accompanying species in microplots of plant communities; however, the process of displacement of these species is predominantly nonselective (random); (2) areas of communities of different sizes with a high and low degree of dominance of S. сanadensis, containing a similar total stock of biomass of accompanying species, include, on average, a similar number of such species; and (3) the species similarity of plant communities located in habitats of different types does not depend on the degree of dominance of S. сanadensis in them. It was concluded that the size of the species pools of cenoses with high and low degrees of dominance of S. сanadensis is approximately the same. Accordingly, an increase in the participation of this species in communities can directly threaten other species only if the area of these communities is relatively small.