Corresponding geographical types of hemiboreal forests in North Asia: peculiarities of ecology and genesis
This study represents a survey of various aspects of the ecology and genesis of a pair of geographically corresponding zonal forest types - West and East Siberian light-coniferous-birch hemiboreal forests. The physiognomic similarities of these communities cause an impression of their plant-geographical and syntaxonomical uniformity. However, they represent two different geographical vegetation types showing essential differences in ecology, floristic compositions and plant-geographical relations. DCA ordination of 70 low-rank syntaxa of North Asian hemiboreal forests and correlation analysis with climatic parameters, demonstrate the importance of special climatic regimes and the influences of Atlantic and Pacific oceans in the formation of floristic differences in geographically corresponding forest types in western and eastern parts of Eurasia. Results of bioclimatic ordination and chorological analysis revealed important geographical trends in the evolution of zonal vegetation types. In case of hemiboreal forests, two different directions of evolution were seen during the last paleogeographical period: 1) Selection of similar cold-tolerant types of life forms during the glacial period because of general fall of temperature in northern hemisphere; 2) Formation of fundamental floristic distinctions in the western and eastern sectors of hemiboreal subzone caused by differences in sub-Atlantic and sub-Pacific climatic regimes and increasing floristic isolation caused by mountains in the central part of continent. Despite the colder, arid and continental climate in the eastern part of Eurasia, East Siberian hemiboreal forests have stronger floristic relations with thermophilous East Asian oak forests than West Siberian forests with European analogues. This fact demonstrates the evolutionary importance of the factor of oceanity-continentality for establishment of specific characteristics of vegetation types. High variability of seasonal temperatures and precipitation is a distinctive peculiarity of monsoon climate determining general ecological-geographical conditions of the whole East Asian sector during the last millions of years.