LAND COVER - Description
Vladimir Stolbovoi

Land cover is an externally observed mosaic of the Earth's surface. It encompasses a diversity of elements that range from natural to artificial and from self-developing to managed. Land cover is a continuum that allows the recognition of different patterns depending on the tasks, methods, and tools applied for delineation, research experience, etc. As stated by the IGBP (1990), none of the land cover products can satisfy all of the many possible applications.

The land cover model
The land cover model is an overview of the present day status of Russian land. The theoretical background of the model stems from the step-by-step rationalization concept proposed by D. Armand (1975). The approach has been applied first to land use and to land cover modeling (Fischer et al., 1995). According to the approach, human activity is assumed to be the main driving force shaping the Earth. Consequently, land cover at the highest level has been organized into natural, semi-natural, and artificial classes. Each of these is subdivided into vegetated or unvegetated subgroups. Furthermore, each of these patterns can be described by finer land-cover elements. The number and level of detail of the finest elements are determined by the smallest unit of characteristics of the data sources that have been used for constructing the land cover database. Thus, these units, derived from the legends of the source maps, play the role of 'building blocks' for constructing a land cover database. These 'building blocks' are, by definition, the finest land-cover units that can be distinguished. By appropriate grouping of the basic units, specific land cover categories can be produced, for instance, for the purpose of modeling vegetation and the terrestrial carbon stock, etc.

On the basis of the model, the following major land cover classes have been distinguished for Russia: cropland, pastures, forest, bogs, swamps, grasses, and shrubs. Technically, the step-by-step method of regionalization has been performed on the bases of the GIS standard map overlap procedure. Figure 1 presents the main blocks of information and the procedure for the land cover elaboration. The databases contain the statistics on the state land and forest account. We associated these data with polygons of vegetation (forest), and land use (cropland, pastures). Wetlands have derived from soils, e.g., swamps have been associated with soils having a thickness of peat horizon from 30-50 centimeters (cm) and bogs link with soils having a peat horizon of more than 50 cm. Grassland and shrubs were taken from vegetation maps. The database on land cover keeps all attributes of the initial databases and allows a wide spectrum of land cover interpretations. For example., it has been used as a basis in the study "Full Carbon Account for Russia" (Nilsson et al., 2000).

Figure 1. Major blocks of information and the procedure for the land cover elaboration.

Results

The proportion of the land cover elements is different for various natural zones of Russia (Figure 2). The share of forested area in the taiga subzones is the highest and gradually decreases in the forest tundra and temperate forest (forest steppe). The proportion of nonforest components of the mosaic within zones indicates major landscape functions of the forests. For example, bog and swamp are common elements for the taiga subzones that illustrate the importance of the hydrological functions that are performed by forest vegetation. It is well-known that covering slopes with forest slows runoff, enhances water infiltration into deep soil, and supports formation of the shallow ground water table. These mechanisms favor development of wetlands that are major reservoirs for organic accumulation in the boreal zone of Russia (Nilsson et al., 2000). It is remarkable that formation of organic horizons in soils with a peat horizon more than 30 cm thick is limited by cold temperature in the tundra and forest tundra environment. However, deep peat (more than 50 cm) is common for the warmer taiga subzones. Temperature constraints mean that there is practically no cropland in the forest-tundra zone. Small plots of cropland occur near industrial centers (Vorkuta, Norilsk) that are used for limited vegetable production. Special thermal cultivation has been developed for this type of production. Southward, the share of forested area in the land cover mosaics decreases as agriculture expands. Simultaneously, the significance of the forest protection function follows this path. In fact, water erosion is evident in the regions where this protective function is ignored and deforestation is overdone.

The proportion of agricultural land in the temperate forest reaches about 50%. However, this expansion mainly occurs at the expense of grassland. It is much easier to cultivate grassland than to clear and plant forest. Forested areas are very scarce in the steppe and semi-desert; they mainly occupy valleys with shallow ground water.

Figure 2. Land cover mosaic by natural zones of Russia.

References
Armand D.L. 1975. Science on Landscapes. Publ. Misl', Moscow, 288 pp.

Fischer G., V. Stolbovoi, I. Savin, and V. Roshkov. 1995. The LUC Approach to Creating a Continental-Scale Land-Cover Database for Russia. WP-95-129, Working paper, IIASA, Laxenburg, Austria, 20 pp.

IGBP. 1990. Global Change. Report No. 12, International Geosphere-Biosphere Programme. Stockholm, Sweden.

Nilsson S., A. Shvidenko, V. Stolbovoi, M.Gluck, M. Jonas, and M. Obersteiner. 2000. Full Carbon Account for Russia. IR-00-021, IIASA, Laxenburg, Austria, 180 pp.

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