Application of Geoinformation Technologies to Assess the Impact of Grazing and Fires on the Vegetation Cover of the North-Western Caspian Region
摘要
In the 1980s, the increase of livestock population in the North-Western Caspian region (up to 3.78 million heads) and non-compliance with pasture rotation regulations led to changes not only in the composition of plant communities but also in their spatial distribution. At the turn of the century, an economic crisis, coupled with a reduction in arable land, the number of farms, and livestock population, resulted in increased in the fire intensity (frequency and burned area), which also affected the state of the vegetation. Currently, pastoral livestock farming is developing in the region. The aim of this study is to assess the impact of grazing and fires on the current vegetation cover of the North-Western Caspian region. The novelty lies in the application of an integrated approach, where the analysis of combined data including ground-based geobotanical studies and characteristics of grazing pressure and fire regime derived from geoinformation processing of remote sensing data, has revealed patterns of vegetation response to pyrogenic impacts and livestock grazing. For this purpose, descriptions of plant communities (240 in the steppe zone and 498 in the desert zone), characteristics of grazing pressure and fire conditions obtained by processing satellite images using geoinformatics methods were used. In the steppe zone, the vegetation cover is dwarf semishrub-grass (Stipa spp., Agropyron spp., Festuca valesiaca, Poa bulbosa, Artemisia spp., Tanacetum achilleifolium) and grass-dwarf semishrub, in the desert zone – bluegrass-wormwood (Artemisia spp., Poa bulbosa) and wormwood-bluegrass. At the final stages of pasture digression, bluegrass (P. bulbosa) and annuals (Anisantha tectorum, Ceratocarpus arenarius, Eremopyrum spp., Salsola tragus) predominate in this area. In our study, the proportion of such communities was 19.6% in the steppe zone and 51.8% in the desert zone, although the load on pastures is practically the same – 0.92 ± 0.10 conventional sheep units/ha in the steppe and 1.02 ± 0.12 conventional heads of sheep units/ha in the desert. The recovery of natural vegetation extends decades and depends on a number of natural (edaphic and hydrothermal conditions) and anthropogenic (grazing and plowing) factors. This process is also slowed by fires, which occur in this region primarily due to human activity. Some years are characterized by a significant amount of dead grass rags, which, when fires occur, facilitates their spread over large areas. Over the past 30 years, the study area has been affected by fires of varying intensity almost annually. For example, 37% of the area in the steppe zone was burned, while in the desert zone, 50.4%. The peak of fire activity occurred between 1998 and 2011. In recent years, the frequency of fires has decreased due to farmers monitoring their pastures more carefully and preventing fires. With the almost complete absence of grazing in specially protected natural areas (the “Chernye Zemli” Nature Reserve and the “Stepnoi” Wildlife Sanctuary), on light soils, highly flammable annual-grass and grass-annual communities have now formed. Frequent fires in these areas maintain the existence of these communities, preventing the development of wormwood communities typical of the desert zone. As is known, when vegetation cover is degraded or destroyed by fires or overgrazing, dwarf semishrubs recover more slowly than grasses. Phytocoenotic diversity in the North-Western Caspian region is determined by the combined impact of grazing pressure and fires.