Transformation of the composition and horizontal structure of steppe communities in East Mongolia under anthropogenic influence and its reflection on large-scale maps

In 1989–1990 participants of the joint Soviet-Mongolian Complex Biological Expedition conducted the works on the estimation of the present-day state of nature ecosystems in Mongolia. The anthropogenic dynamics (transformation) of steppe ecosystems was studied in the East Steppe Stationary in the territory of state-farm Tumen-Tsogt in the Sukhebator District. During these works the series of maps was compiled for the territory of state-farm and for separate key plots (S. 1 : 1 000 000; 1 : 200 000; 1 : 100 000) showing the anthropogenic change of vegetation of animal populations, of soils and of ecosystems as a whole. The article represents some results of the investigations on transformation of vegetation cover under grazing the leading anthropogenic factor in Mongolia. The basic map is the vegetation map in scale of 1 : 100 000 (fig. 1, fragment). The legend of this map reflects the relations between vegetation and relief and soils. The highest divisions of the legend represent the vegetation of major forms of relief: «Vegetation of low mountains», «Vegetation of flat alluvial-deluvial plains», etc. These divisions subordinate the subzonal and altitudinal-subbelt types: «Rich in forbs grass meadow steppes on the mountain chernoziom soils», «Forb and forb-bunch grass steppes on the dark-chestnut soils», etc. The communities and their combinations, belonging to the definite edaphic variants of zonal vegetation, are taken as mapping units. 7 edaphic variants are distinguished in the whole. In the legend the concrete series of transformation of vegetation cover are given. Numbers 1–17 represent the undisturbed communities. The figure indices at the numbers (for instance: 10'–104) differentiate communities of the same digression serie - fr om less to most degradated ones. In the case of fallow lands such indices indicate the stage of reconstruction – from less to the most reconstructed vegetation (18–185). It has been paid attention to the heterogeneity of vegetation that is reflected in the map legend in characterizing the map divisions. The attention has been attracted also to the pattern of the horizontal structure of these complexes. The classic complexes of plant communities are not characteristic of the steppe zone of Mongolia, especially of its central and eastern regions as they are characteristic, for instance of the Kazakhstan steppes wh ere their distribution and development are caused by the processes of salt accumulation and salt removing from soils. In Mongolia the heterogeneity of vegetation and soil cover is conditioned by the burrow activity of rodents. The patterns of horizontal structure of phytocoenotic complexes appeared to be diverse and peculiar of definite landscapes depending on animal population and environmental conditions. It was ascertained that at grazing not only the phytocoenotic parameters (species composition, coverage, abundance, etc.) are transformed but also community dimensions, their proportion in complexes and the pattern itself of these complexes. It was interesting to reveal the transformation series of these patterns in complex biogeocoenoses. Fig. 2 shows the fragment of map representing the horizontal structure of biogeocoenoses, s. 1 : 1 000 000. The legend of the map is given in the table form (see table). The map shows both the reconstructed and the actual structure of vegetation cover. The undisturbed and slightly disturbed structural types are given by the main numbers (1–12) with figure index 1 (V–12'). The structures disturbed in various extents are shown by figure indices at the main number (for instance, 22–24). The indices correspond the degree of disturbance: 2 – middle disturbed, 3 – strongly disturbed, 4 – the most disturbed. The schematic drawings of horizontal structure of the natural and transformed complexes of plant communities are given in figure 3. Figure 4 proposes the fragment of analytic map of horizontal structure of biogeocoenoses. This map shows the actual pattern of plant community complexes. The last map (fig. 5) represents the percentage contribution of zoophytochoras in background undisturbed vegetation in various landscape elements.