STRUCTURE OF STEPPE ZONE IN EURASIA IN THE LIGHT OF THE CONCEPT OF ECOTONES

 

V.V. Neronov

A.N. Severtsov Institute of Ecology and Evolution of RAS 117071 Moscow, Leninsky pr, 33, Russia

 

The "classic" paradigm of physical geography puts at the first place a comprehensive analysis of natural zonal geosystems of the Earth. Meanwhile transient natural complexes widespread along zonal geosystems have appeared considerably less studied, specially by way of structural organization and functioning. The development of the concept of ecotones led to a conclusion on the independence of such complexes having distinctive characteristics, particular properties and structure. Usage of the concept of ecotones allows to contour steppe zone boundaries more reasonable and to show features of its geosystems presented on the territory from northern forest-steppe up to southern semidesert.

Traditionally within the Eurasian steppe botanic geographical region researchers set aside meadow, true (typical), dry and desert subzonal types of steppe communities. In this case into one type of vegetation cover there are integrated the different on phytocoenotic features, structure, rhythm of development and ecology of major coenospecies communities, of which the meadow and desert steppes are shaped. The justified allocation in a rank of separate independent natural zones of forest-steppe and semidesert allows more precisely to contour boundaries of the proper steppe zone, having included in it only true steppe communities with characteristic structure, functioning and rhythm of development. In this case the allocation only two subzones is expedient:   forb-bunch-grass steppe

(northern subzone, true steppes) and bunch-grass steppe (southern subzone, dry steppes). The meadow steppe subzone thus will enter a structure of the forest steppe zone, and semidesert and desert steppes -into a structure of the semidesert zone.

On recent geobotanic maps the forest-steppe together with forb-grass and grass-forb meadow steppes and steppe meadows in combination with forest communities is referred to the steppe type of vegetation cover. At the same time, the numerous data are accumulated in favor to allocate the forest-steppe as an original zone of transient character. A physiognomy of its communities (peculiar landscape of a park type), special and eco-biomorphological composition (the meadow mesoxerophyte as a characteristic life form of herbaceous plants; special habitus of woody plants), particular conditions of habitats and some other features are testified to a qualitative originality of forest-steppe vegetation. The studies of forest-steppe fauna (on the pattern of insects, birds and mammals), have revealed a significant number of autochthonous species composing the historically conditioned and ecologically adapted forest-steppe faunistic complex.

The zone of semideserts represents a gradual transition from the true steppe to the desert. On our view, the allocation of a semidesert as an independent zone with an allocation of two subzones (northern and southern semidesert) is most correct. From the geobotanic point of view the semideserts can be described by approximately equivalent domination on interfluves of tall and small cespitose grasses representing a zonal life form of steppes and drought-resistant xerophytic dwarf semishrubs uniquely determining appearance of deserts. Among prominent features it is necessary to point to the sharply expressed microcomplexity. In such complexes there are participating not only units of adjacent natural zones (steppe and desert), but also qualitatively peculiar desert steppe ones. For this reason they gain properties the contact ecotone geosystem. It is indicative, that representative zonal semidesert geosystems are widespread in middle part of forming microcatenas. Thus, even on a microlevel it appears ecotone character of territory (between steppe parcels of microhollows and desert ones at microelevations). The fauna of semideserts can not be shown as a simple conglomerate from steppe and desert species, and it forms, apparently, peculiar faunistic complex. Many species inhabiting on the given territory find here the ecological optimum and reach high and stable numbers.


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