REGULARITIES OF FOREST FORMATION PROCESS IN SOUTHERN TAIGA BIRCH FORESTS

Methods of the objective periodization of the age dynamics of forest stands are considered on the example of southern taiga birch forests in the process of demutational changing birch ( Betula L.) to spruce ( Picea A. Dietr.). The analysis of the age range of birch forests has allowed to determine four distinct stages of age development which differ one another by the qualitative state of birch population. There are Stage of regeneration (before forest canopy has closed), Stage of youthfulness (before “quantitative maturity”, when the curve of mean annual increment of trunk volume of trees at peak), Stage of maturing (from “quantitative maturity” to “natural maturity”, when the curve of trunk volume of trees at peak) and Stage of ripeness (from “natural maturity” to full treefall of first layer of forest). Then, according to the determined stages of age development of main breed, the phases of age dynamics of birch forests have been defined: Phase of young birch forest formation, Phase of active growth of birch and appearance of spruce under birch canopy, Phase of two layers tree stand - first tree layer of birch, second tree layer of spruce, Phase of changing of chief breed in forest as result of death and treefall of birch trees.