Understanding of the key species coenopopulations structure of late-successional forest communities serve as a model of the forest ecosystems state and stability in the organization of sustainable forest management and conservation of biological diversity. The ontogenetic and age structures of cenopopulations of the key species, Pinus sibirica DuTour and Abies sibirica Ledeb., were studied in a climax S Siberian pine forest with Vaccinium myrtillus L. and green hypnum mosses (the most common forest type among taiga forests of the East Sayan mountains). The permanent sample plot (50×50 m) was located in the northeastern part of the Idarskoe Belogorye ridge of the East Sayan in the middle part of a westerly slope with a steepness of 2 degrees, at an elevation of 1000 m a.s.l. (54°44'N, 96°07'E). The forest stand had low productivity (quality class V), high closeness of crowns (about 1.0) and mixed composition with predominance of P. sibirica, which are characteristic of the mountain-taiga cedar forests of the Eastern Sayan (See Table.). We performed general geobotanical description, measurement of size and age, assessment of ontogenetic and sanitary states of each tree, as well as assessment of reforestation on the sample plot. P. sibirica coenopopopulation had a wide age amplitude (from 1 to 200 years) and absolutely uneven-aged structure, mass reforestation (more than 3000 ind./ha), large sizes of mature individuals (maximum diameter - 58 cm, height - 21.3 m), predominance of the number (70% of the total density of the forest stand) and timber stock (95%). The ontogenetic structure of P. sibirica cenopopulation was characterized by a normal state (See Fig. 1 and 2) with a sharp peak of the distribution and distinct left-handed skewness (coefficient of asymmetry - 2.0; kurtosis - 4.1). This corresponds with the concept of consistent self-reproduction and stability of forest ecosystems. A. sibirica was inferior in terms of the reforestation number (1575 ind./ha), life expectancy (up to 110 years) and the size of mature trees (maximum diameter - 22.7 cm, height - 16 m). The ontogenetic structure of A. sibirica cenopopulation (See Fig. 1 and 3) is characterized by a complete spectrum and more distinct left-handed skewness. Thus, P. sibirica had a clearly expressed competitive population strategy. A. sibirica showed indications of phytocenotic tolerance. It is obvious that sustainable forest ecosystems in the absence of anthropogenic pressure in the mountain-taiga forest belt conditions is formed in the process of continuous change of P. sibirica age generations.
Cenopopulation structure of the key species in Siberian Pine mountain-taiga forests of the East Sayan mountains