Proliferation of Alien Plant Species in Forest Communities of the Khosta Yew–Boxwood Grove of the Caucasus Nature Reserve after the Destruction of Buxus colchica Pojark

At early stages of successions initiated by the destruction of Buxus colchica, 58 alien plant species have been registered in the Khosta yew–boxwood grove, including 14 species that actively penetrate into natural forest phytocoenoses. One to eight alien grass species were identified on sampling plots 400 m2 in size, which amounts to 8–57% of the total species richness. The maximum number of alien species was noted in forest communities with the tree canopy density of 0.4–0.7 in the upper story. The grass–dwarf-shrub layer on such sites has been formed under the conditions of relatively good insolation and relatively low projective cover of dominant species. At the same time, alien grass species demonstrate the highest competitiveness level in forest communities with high tree canopy density; such communities have no clearly manifested dominants in the grass–dwarf-shrub layer owing to the poor insolation.