[Coenotic distribution and ecological preferences of Betula pendula and Betula pubescens in Central Russia].

Betula pendula and B. pubescens are widespread species inhabiting the forest zone of Russia. At the same time, they are closely related species making up transitional forms. It is believed that their ecological ranges are overlapping to a great extent, although B. pubescens is more hydrophilic than B. pendula and less exigent to sunlight. These data, obtained by means of empirical observations, help to understand the ecology of both birch species but so far are not statistically proved. An analysis of habitat distribution of the two birch species is carried out, and a comparison is performed of their ecological relations with such factors as humidification, trophic status, acidity, illumination, and nitrogen soil richness (graded by D. Tzyganov scales). It is shown that B. pendula and B. pubescens differ significantly with relation to humidification, soil richness, nitrogen concentration, and illumination, while do not differ with relation to acidity. Habitat preferences indicate that B. pubescens is more eurytopic species than B. pendula. Although synecolog-ical ranges of both species overlap, their synecological optima still clearly stand apart.