Phytocoenotic diversity and spatial structure of pine forest-steppe landscapes (Dzhida river basin, Republic of Buryatia)

The spatial structure of vegetation, representing pine forest-steppe landscapes of south part of Buryatia (on the example of key site) werestudied. On the basis of 225 releves 17 types of plant communities were identified. All assigned communities were organized in a two-level hierarchical system. Each type has a brief description, phytocoenotic and ecological characteristics. The conducted analysis showed a high phytocoenotic diversity of studied key site. Selected plant communities compose more separate categories of high units of vegetation including not only zonal types, but also edaphical-climatical types. The spatial structure of vegetation was studied with using ordination, landscape profile and hill model methods. Ordination analysis revealed two groups of plant communities on the first axis. First group was formed by mountain steppe plant communities - shrub, petrophytic as well as dry pine forests, whose floristic composition is similar to steppe communities. This group associates all components of mountain pine forest-steppe which form a specific regional type of mesocombination of expositional forest-steppe. The second group is formed by communities connected not only with sand and sandy soils, but with similar zonal types of bunch-grass steppe on flat aprons with light sabulous chestnut soils. The spatial structure of vegetation in the conditions of leveled relief and terraced depressions has quite a simple character. Usually, it is formed by homogenic patches of bunch-grass steppe communities. The second axis is connected with soil richness. The saz steppes with Achnatherum splendens and hemipsammophytic communities with Calamagrostis epigeios are on the edge of this gradient. In general, the ecological analysis helped to define the factors of high phytocoenotic diversity of vegetation. Firstly, it is the maturity of soil profile, the level of stone and sand fractions in the soil. Our studies showed that moisture is not a driving factor at the key site. This can be proved by prevalence of steppe plants in all types of plant communities and also by hill model which showed small differences of moisture for different aspects of slopes. The development of such arid versions in mountain forest-steppes can probably be explained by hydro-thermic conditions of Dzhidinskii-Dyrestuiskii depression of Selenginskii middle mountainous region of Buryatia where desert-steppe climate conditions with spring hot dry winds are usually found.

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