Ontogenetic structure of coenopopulations of Juniperus sibirica Burdst. and Betula rotundifolia Spach on new moraines of the Maly Aktru glacier (Central Altai, Severo-Chuiskiy range)

Colonization peculiarities and ontogenetic structure of coenopopulations of two shrubs Juniperus sibirica and Betula rotundifolia were investigated at different stages of vegetation development on new moraines of the Maly Aktru glacier (2200-2290 m a.s.l., Aktru headwater basin, Severo-Chuiskiy range). Colonization of J. sibirica can occur in early years after glacier retreating. The first individuals on some sites probably don't survive dying when they are young because of unfavorable conditions. B. rotundifolia colonizes new moraines not until 40 years after glacier retreating at the herb-moss-willow stage of vegetation development and depends on the presence of plane sites offine fragments of rocks protected from cooling by the glacier and with a considerable snow cover. The time period of new moraine forming is not enough for passing overall ontogenesis by individuals of this species. Seemingly, the absence of the youngest individuals of J. sibirica is connected with unfavorable weather conditions in the years of investigations and/or low germinating ability. A settlement of the youngest individuals of B. rotundifolia at the herb-moss-willow-birch stage is hampered by dense moss cover and leaf litter. These are reasons why the ontogenetic spectra of all investigated coenopopulations of this species are incomplete. The series of J. sibirica cenopopulations from invasional cenopopulation at the pioneer stage to the young and normal ones at the herb-moss-willow-birch stage and on the end moraine of the middle of the 19 century were observed. The series of B. rotundifolia cenopopulations from the young and normal cenopopulation at the herb-moss-willow stage to the mature and normal one at the herb-moss-willow-birch stage were revealed. Coenopopulation of J. sibirica at the pioneer stage isn't capable yet of self-sustaining and completely depends on seed influx from without because of the absence of generative individuals in its structure. Self-sustaining of its other coenopopulations can occur by their own seeds as there are generative individuals. All coenopopulations of B. rotundifolia are capable of self-sustaining by seed reproduction due to the presence of generative individuals and also by partial formations at the herb-moss-willow-birch stage. The character of ontogenetic spectra and demographic characteristics of species cenopopulations depend on the age of moraine deposits, substrate features, micro- and mesoreliefpeculiarities, ecotopes protectedfrom cooling by the glacier and a sufficient snow cover.

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