VEGETATION DIVERSITY ON THE MICROSITES CAUSED BY TREE UPROOTING DURING A CATASTROPHIC WINDTHROW IN TEMPERATE BROADLEAVED FORESTS

РАЗНООБРАЗИЕ РАСТИТЕЛЬНОСТИ НА ЭЛЕМЕНТАХ ВЕТРОВАЛЬНО - ПОЧВЕННЫХ КОМПЛЕКСОВ Abstract. We analyzed the diversity of vascular plant species growing on microsites formed after tree falls with uprooting as a result of catastrophic windthrow that occurred in the temperate broadleaved forests of the Kaluzhskie Zaseki Reserve in 2006. Size characteristics of pits and mounds formed by uprooting of 110 individuals of 9 tree species were measured. Vegetation on microsites formed by 45 fallen trees of 8 species was described. We distinguished the following microsites: 1) top of the mound; 2) back side of the mound; 3) front side of the mound (from the trunk side); 4) pit over the mound; 5) pit in front of the mound in the case of rotational treefalls; 6) part of the trunk close to the roots (deadwood). Vegetation on 45 plots of 1x1 m in size and located close to but not affected by tree uprooting (reference plots, or reference communities) was also described. The results of the indirect ordination analysis revealed that the ecological and phytocoenotic microsites; 6 species were not found before the windthrow study in the descriptions of broadleaved and aspen forests of the Reserve, and 8 species were found in the descriptions of those forests no more than three times. New species are mostly species from the boreal ( Phegopteris connectilis, Sambucus racemosa ), nitrophilous ( Rubus caesius ), water-marsh ( Epilobium hirsutum , Epilobium palustre ), meadow-edge ( Bromopsis inermis , Hypericum hirsutum , Conyza canadensis , Vicia cracca ), and piny ( Calamagrostis epigeios ) ecological-coenotic groups. In general, the increase in plant diversity in the area of catastrophic windthrow is caused by the massive emergence of new microsites (pits, mounds and deadwood) and the subsequent appearance of species with different ecological and coenotic traits.