Changes in principle characteristics of the phytocenoses with participation of Larix sibirica Ledeb. in the upper treeline ecotone in the Polar Urals

The purpose of our work was to evaluate the current state of phytocenoses with Larix sibirica Ledeb. (floristic diversity, structure, some aspects of production and destruction processes) for altitudinal profile I, introduced by SG Shiyatov in the 1960-s in the upper treeline ecotone in the Polar Urals. Along the altitudinal profile (182-300 m a.s.l.) near mount Chernaya (66°47'-66°49' N, 65°30'-65°35' E), the estimation of the basic features of the investigated phytocenoses revealed the following peculiarities of the vegetational cover formation in the ecotone of the upper forest limit in the Polar Urals. The significant floristic similarity of the phytocenoses is caused mainly by mutual species of herbaceous plants. Along the altitudinal gradient - from larch forests and open woodlands to tundras with single trees - increased the share of species of the Arctic fraction and correspondingly decreased the share of more thermophilous species of the Hypoarctic and Boreal fractions in the cenofloras composition. The total phytomass store decreased significantly. Only the aboveground phytomass of the herb-dwarf shrub layer was relatively stable, however the correlation between its individual components varied greatly, as well as in the ground vegetation (moss-lichen / lichen-moss). Both the annual growth of the aboveground parts of vascular plants (in its structure the share of annually dying off components with slower destruction rate increased) and the mass of thin roots and rhizomes decreased. Destruction processes were slower on the whole. Moreover, in the tundra phytocenosis during the period of investigation the unsteady moistening regime of the ecotope was one of the leading environmental factors. Production and destruction processes in the larch phytocenoses were rather intensive in the Polar Urals than in some other regions of the Subarctic. Acknowledgments: This work was financially supported by INTAS, Grant No. 01-0052. The author expresses her sincere gratitude to Mazepa VS, Dr. Sci. (Biology), head of the laboratory of dendrochronology, Institute of Plant and Animal Ecology, UD RSA (Yekaterinburg, Russia) for the provided tree layer material. The article contains 4 tables, 20 ref.

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