Species pool, species richness, density compensation effect, and invasibility of plant communities

The published data on the resistance of plant communities to invasions of alien species are discussed. It is shown that the variation in the number of such species on small areas of cenoses depends on the balance between their local richness and species pool size. This ratio has been used to predict the degree of invasibility of natural plant communities in Western Caucasus (alpine low-grass meadows and heaths, subalpine middle-grass meadows of high-altitude mountain massifs and ridges isolated or not by forest communities, and tree layer of mountain forests). The results demonstrate that the communities with high species richness, isolated, evolutionarily young, and disturbed in their previous history display a higher invasive potential.