Experimental evaluation of shading effects in seasonal dynamics of four alpine communities in northwestern Caucasus, Russia

Light plays a significant role in determining composition of alpine communities. A series of 3-yr experiments to assess four alpine communities' responses to a severe reduction in insolation regime (95% reduction for the whole, first, or second half of the growing season) were carried out on Mount Malaya Khatipara, Karachaevo-Cherkessia Republic, northwestern Caucasus, Russia. The snowbed community developing under the deepest snow had the highest proportion of shade-tolerant species among the four communities. In contrast, the alpine lichen heath developing under little, or no snow accumulation was the most susceptible to shading. The heath lost over 70% of species after 3 yr of the all-season shading. The intermediate grassland and meadow lost ca. 50%, while the snowbed lost only 18%. Members of Cyperaceae, family and evergreens Vaccinium vitis-idaea and Gentiana pyrenaica were the most shade-tolerant species, while most other species showed little tolerance of shading, particularly when shaded for the whole growing season. Two ephemeroid species increased their shoot numbers when shaded during the second half of the growing season. Generative shoots of all species showed greater relative decrease than the vegetative shoots of the same species. Snowbed species showed the most varied response. This is consistent with earlier findings of opportunistic character of snowbed flora. The snowbed species will be most adaptable to any possible future shifts in vegetation composition under climate change.