Dimensional and age structure of mountain Siberian stone pine forests of the Cis-Yenisei Sayan

The structure of the Siberian stone pine Pinus sibirica Du Tour stands was studied using the example of late-successional chern Siberian stone pine forests with sedge, tall herbaceous and large forest ferns and mountain-taiga Siberian pine forests with bilberry and green hypnum mosses that are widespread in the North-Altai-Sayan and the East-Sayan (respectively) mountain forest vegetation province of the Altai-Sayan mountain ecoregion. A comparative structure analysis of stands by age, diameter and height was carried out in two significantly different climatic zone conditions. The Siberian stone pine stand in the chern sedge, tall herbaceous, large forest ferns Siberian stone pine forest has a wider age range (from 60 to 560 years) and a cycle type of long-term dynamics. The age composition of the Siberian stone pine stand in the mountain-taiga blueberry, green hypnum moss Siberian stone pine forest has a smaller amplitude (from 60 to 220 years) and belongs to an absolutely uneven-aged structure type. Despite the differences in the age composition of stands, the long–term development of both late-successional Siberian stone pine forests led to the formation of similar unimodal distributions of the data of stands structure by diameter and height, which, apparently, provide the most effective interaction of the keystone species with the environment. The dynamic stability of chern sedge, tall herbaceous, large forest ferns Siberian stone pine forest under conditions of abundant rainfall, high soil fertility and powerful development of lower layers vegetation is provided by the increased spatial heterogeneity of phytocenosis, a complicated interaction between the Siberian stone pine and the Siberian fir Abies sibirica Ledeb. populations and high lifespan of the Siberian stone pine trees. The resistance of mountain-taiga blueberry, green hypnum moss Siberian stone pine forests structural-functional organization in less favorable climatic zones conditions is formed by mass, almost permanent natural regeneration of the Siberian stone pine and stable tree recruitment in separate gaps. Thus, fundamental differences in the structure and dynamics of the Siberian stone pine coenopopulations in hyperhumid and humid climatic facies of the Altai-Sayan ecoregion are shown on the example of two representative objects. The results of the study can help predict main possible trends in the forest ecosystems transformation in different scenarios of natural and anthropogenic changes.