Phytoecological mapping of the Northern Caspian Region

Abstract

We have performed the phytoecological mapping of the Northern Caspian Region in scale 1 : 2 500 000. The territory includes the Caspian Lowland and the Mangyshlak Peninsula between 45°-53°30 E and 49°-42° N. The earlier published maps of the same scale showed either vegetation of the Caspian Lowland or that of the Mangyshlak Peninsula. We have shown both territories on one map, which has permitted to reflect the peculiar features of the Northern Caspian Region: extensive distribution of the dwarf-semishrub communities not only in desert but also in the steppe zone; differences of desert vegetation cover between areas west and east of the Ural River; the running of zonal steppe/desert boundary along 44° N on the west coast of Caspian Sea whereas on the east coast the middle deserts occur at the same latitude: etc. Our studies were based upon a broad understanding of the desert and steppe types of vegetation. To the desert type of vegetation on the plains of Caspian Region and Turan belong the communities of xerophilous and hyperxerophilous micro- and mesothermic plants of various growth forms, mostly dwarf-semishrubs, semishrubs and shrubs, to the steppe type - plant communities consisting mostly of perennial more or less microthermic xerophilous herbaceous plants, predominantly of bunchgrasses, locally tufted sedges and perennial herbs. One should add that stony-rubble and salted substrates in steppe zone are characterized by distribution of dwarf-semishrub communities. Some researchers, apart from steppe and desert zones distinguish semidesert one in the Caspian Lowland, however it is accepted that there is no semidesert type of vegetation. Therefore it is difficult to agree with the recognition of the semidesert zone. The drawing of zonal boundary between steppe and desert in the Northern Caspian Region involves definite difficulties depending on environmental features of the region and strong anthropogenic press. So, on sand massifs and saline soils vegetation is the same both in desert and steppe zones. Vegetation cover of the Western Caspian Region is transformed considerably under anthropogenic influence. It is known that in steppe region at ploughing up of the worm- wood-bunchgrass steppes one of the stages of restoration of fallow lands is the wormwood one, physiognomically similar to desert. The same appearance is assumed by steppe at the strong grazing when grasses are destroyed and wormwoods is growing up. Such anthropogenic wormwood communities are widely spread at the boundary between zones. This resulted in that on earlier published vegetation maps the desert zone in the interfluve of Volga-Ural was shifted fairly far to the North up to 49°N. At present we believe that it is possible to assign the northern part of Ryn-Sands to steppe zone and to draw the zonal boundary along the latitude of 48°30 N. The boundary is determined by climate, geological history, hydrology, edaphic conditions and. vegetation. Somewhat differently than earlier we draw the zonal boundary in the Caspian Lowland between the Volga River and the Ergeni Height. It goes from Prishib's settlement to south-west to Yashkul's settlement (45°30 E) and further westward of Achinery's settlement to south-east up to the Kuma River. We could specify its position since during the last years the part of fallow lands, occupying large areas to the west and north of this line, restored up to steppes of Stipa sareptana-Artemisia lerchiana and those of Agropyron desertorum-Artemisia lerchiana. In the course of cartographic works we compiled the vegetation map of the Northern Caspian Region. This map became the base for series of maps: phytoecological one. the map of dominating plant formations, the map of edaphic variants of plant communities, the map of transformation of ecosystems of the Lower Volga Region. Phytoecological map (Fig. 1) gives an idea of latitudinal differentiation of vegetation in the Northern Caspian Region which depends on climate, and reflects its interrelation with soil conditions on plains and with lithological composition in low mountains. The map of edaphic variants of plant communities (Fig. 2) well reflects the peculiar features of various parts of the Northern Caspian Region: between the Terek River and the Ural River psammophyte and hemipsammophyte variants there predominate; east of the Ural River halophyte ones prevail: on the Mangyshlak Peninsula all variants are represented. Pelitophyte variants predominate in the west of the Region and along its northern margin within the limits of steppe zone. On the map of dominating formations (Fig. 3) we could show the distribution of 17 formations and 1 group of formations. A part of formations is restricted exclusively to steppe zone or desert zone, another part is spread throughout the both. This map helps to understand such peculiar feature of the region as wide distribution of dwarf-semishrub communities not only in deserts but also in steppes, which is due to presence of large areas of sands and saline soils in region. The Caspian Region was intensively used by man for a long time. By present time vegetation cover is noticeable transformed. We tried to show cartographically the degree of this transformation and differences in economical utilization of the Lower Volga area (Fig. 4). 4 degrees of transformation are distinguished: Tl-weak, T2-moderate, T3-strong, T4-very strong. Each polygon is considered from standpoint of type of anthropogenic influence: such as pastures (index «a»), fallow lands (index «b»). For pastures degree of grazing is recorded - from weak grazing to overgrazing. For fallow lands the stage of restoration is detected: from the tall weed one up to the perennial herb one conventionally restored.