M.V. Lomonosov Moscow University, Vorob'evy Gory, Moscow 119899, Russia

Abstract

Long term experiments in 4 alpine communities are reviewed. Alpine lichen heath (ALH). Festuca varia dominated grasslands (FVG). Geranium gymnocaulon - Hedysarum caucasicum meadows (CHM) and snow bed communities (SBC) were the main objects of investigation. Responses of the species to reciprocal transplantation between communities were varied. As a rule, dominants of ALH and SBC (communities, developing under severe ecological conditions) positively responded when transplanted to more productive meadows and grasslands in absence of competition with native plants. On the other hand, dominants of alpine meadows and grasslands showed negative responses when transplanted to the more severe conditions of ALH or SBC. Some species developed better in the original communities. Population density of the most species increased significantly in the absence of neighbour species. Experimental removal of five main dominants was studied in ALH. While the dominant plants increased the number of their shoots relative to the control after the removal of their possible competitors, most subdominant species in the community responded negatively by decreasing the number of shoots. Alpine lichen heats have a specific structure: small lichen patches alternate with patches of vascular plants. The authors suggest that in poor shallow soils, the roots of vascular plants occupy larger area than their above-ground shoots. Thus, some vacant space becomes available for fruticose lichens as there is no significant competition for nutrients with vascular plants. Several experiments (removal of lichens, fertilization, root cutting) were carried out to prove the hypothesis. Shading experiments showed possible phenological divergence between species in GHM, where competition for light took place. Alpine species differently changed soil properties in monoculture. The lowest soil nutrient concentrations were observed for Carex sempervirens (NH4), Antennaria dioica (K), Hedysarum caucasicum (P), Geranium gymnocaulon (Ca). The authors concluded that resource competition is an important mechanism to determine the structure of alpine plant communities, but facilitation plays significant role in severe environment as well.