In the paper the legend for 8 vegetation maps of key polygons s. 1 : 200 000, compiled by unified method, is given. The maps characterize the state of vegetation cover in different parts of the Lower Volga River (Volga-Akhtuba flood-plain and delta) in the late 90th.
The Volga-Akhtuba flood-plain is well-divided into 2 morphogenetic types: the river-side flood-plain and the inner (central) one. Delta consists of numerous islands separated by channels and is subdivided into 3 parts: upper, middle and lower ones. At the mapping of flood-plain vegetation it is important to reveal the spatial variations in vegetation cover connected with regime of inundation, topography elevation, structure of surface, ground water table. The generalized legend to all maps is constructed according to ecological-dynamic principle reflecting the composition and structure of vegetation cover. Large divisions correspond to differentiation of vegetation at the level of main topographic types of territory: A. Vegetation of flood-plain, Б. Vegetation of delta. The divisions of the next rank are: I. Vegetation of river-side flood-plain and II. Vegetation of the inner flood- plain. Within the delta the following division are distinguished: 1. Forest-shrub- meadow and riparian-aquatic vegetation; 2. Desert vegetation. Mapping units proper (marked by numerical indices) characterize the phytocoenotical and floristic composition of vegetation as well as different patterns of its spatial structure and dynamics among the different elevation levels and forms of relief.
Construction of Data Bases (DB) at mapping process has its specific features. Map organizes and differentiates the process of collecting information itself. The main instrument in this process is the map legend and the contents of mapping units. The botanical-cartographical DB suggests storing already synthesized and classified information, presented in form of mapping types of geobotanical polygons along with indices of environmental factors.
The flood-plain vegetation of the Lower Volga River is represented by forests, shrub thickets, meadows, and aquatic-riparian Herbaceous communities. The forests are restricted mainly to the inner gentle ridges flood-plain. Oak forests (Quercus robur) are characteristic of only northern part of the Lower Volga River occuring between city of Volgograd and Kapustin Yar settlement. Willow forests (Salix alba) are spread throughout the all Lower Volga River (from Volgograd down to the Caspian Sea). They predominate in delta. In the middle part of delta the groves of Elaeagnus angustifolia appear.
The channel-side natural levers of the lower seaward part of delta are occupied by forests of Salix alba. Shrubs thickets are less characteristic of these habitats; Tamarix ramosissima should be mentioned which appears south of 48°N in Volga- Akhtuba flood-plain in the limits of the Northern desert subzone.
Forests of Populus nigra are wide-spread in the Volga-Akhtuba flood-plain from city of Volgograd southward up to Selitrennoye village. However they occupy habitats of middle topographical level. The same level in the river-side flood-plain and delta shrub thickets occupy. They are formed mainly by willows — Salix triandra, S. viminalis, S. acutifolia.
Meadow vegetation predominate in the Lower Volga valley. Vegetation of high topographic level is formed by meadows of Calamagrostis epigeios, Bromopsis inermis, Elytrigia repens. Meadows of the middle topographic level are represented by grass-sedge communities. Meadows of the low topographic level are formed by communities of Carex acuta, Eleocharis spp., Elytrigia repens, Phragmites australis, Butomus umbellatus.
The riparian-aquatic vegetation is formed by the communities of Phragmites australis, Typha spp., Scirpus lacustris, Phalaroiodes arundinacea, Butomus umbellatus, Sagittaria sagittifolia, Sparganium ramosum along the shores of water bodies and on the bottoms of depressions.
Communities-indicators of soils with high salt content are characteristic of delta vegetation. On the overmoistened islands, free of water for a short time, with the surface salinification, the communities of Aeluropus spp., Crypsis aculeata, Bolboshoenus maritimus, Suaeda confusa, Salicornia europaea, Cynodon dactylon are spread.
Interactions between aquatic vegetation, hydraulics and fine sediment
