Natural background and anthropogenic drivers of vegetation cover changes in pasture landscape: the case of Central Mongolia

The article analyzes natural, first of all, geomorphological and lithological-edaphic conditions and anthropogenic (increase in livestock and change in the structure of the herd) factors determining the degradation of vegetation in the landscapes of the desert steppes of Mongolia. The sources for the assessment of vegetation cover were the images of Landsat 5 and 8 by which were calculated NDVI index, a joint index of the BSI + LDI and the synthesis of channels for 7—5—3 (Landsat 8) and 7—4—2 (Landsat 5). To assess the role of natural conditions in ArcMap package was built model of geotopes, containing data on the absolute height of the area, its position in the system of landscape levels, the genesis and the type of ground. The analysis of the contribution of anthropogenic factors is carried out on the basis of statistics on somons. It was revealed that in 1990—2015 the number of cattle varied from 1.1 to 2.8 million heads, and in all somons (districts) of Srednegobiisky aimag (region) the increase in the number was due to sheep and goats. It was found that a 47 % of the area of aimag has reduced vegetation cover, and to the greatest extent these processes are typical for different formations of the desert steppe subzone in the Northern and Central parts of aimag. Verification of the obtained results was carried out according to the data of field studies of the Russian-Mongolian complex biological expedition of RAS and AMS. Landscapes potentially susceptible to degradation occupy 60 % of the aimagʼs territory. Among the already transformed landscape sites eluvial and transeluvial geotopes of the socle plains on rocks of mixed composition prevail. It is shown that under similar trends of livestock changes pasture ecosystems of somons with predominance of such landscape sites are more prone to degradation than others.