Result of Impact of Dominants on Species Richness of Plant Communities: Ordered or Random Species Loss?

The question of the nature (random or ordered) of the loss of species in plant communities as a result of an increase in the participation of dominants is considered. The objects of study were 15 sites of communities of different types: riverbanks, forest meadows, steppes, subalpine and alpine meadows of the Western Caucasus, macrophytobenthos of the Sea of ​​Azov. Two approaches were used: in the 1st one, the data on biomass samples taken from micro-sites of communities with differing participation of dominant species were compared with series of model cenoses with a random distribution of species; in the 2nd, groups of samples were compared with differing participation of the dominant, but with equal total biomass of accompanying species due to the different numbers of samples in groups. As a result, a well-pronounced effect of ordered disappearance of species was revealed only in three areas (dominated by Rubus caesius , Glycyrrhiza glabra , and Solidago сanadensis ). In other cases, the distribution of species over micro-sites with differing participation of the dominant was random. This means that the increase in the participation of dominants leads mainly to an indiscriminate displacement of other species.