Zharnikova M.A., Alymbaeva Zh.B., Garmaev E.Zh.
Baik al Institute of Nature Management SB RAS, Ulan-Ude, Russia E-mail: rita_zharnik ova@mail.ru
Climate changes and irrational nature management lead to the transformation of vegetable cover. During the last decades an increased grazing pressure on ecosystems has changed nature balance because of higher vul- nerability of semiarid and arid ecosystems, entailing their degradation and desertification [1].
Today extremely great consideration is given to spatial and temporal dynamics of steppe plant associations in order to estimate their reactions to the present climate changes.
Mongolia has a unique complex of natural and climatic conditions and inimitable landscapes. Which have been causing interest for the scientists of different specialties for ages. Mongolian ecosystems have been studying for decades [4]. When investigating Mongolian steppes the main tasks were aimed at transformation processes identification, including soil and vegetation degradation. These investigations are reflected in the numerous scien- tific papers of such scholars as Yunatov A.A. (1974), Lavrenko E.M. (1970, 1978, 1980), Banzragch D., Kar- amisheva Z.V., etc. (1978), Kazantseva T.I., etc. (1988, 2012), Dashnyam B., etc. (1974).
The climate of dry Mongolian steppes is characterized by strongly pronounced continentally which is caused due to the location of the country in the centre of Eurasian mainland. This type of climate is formed under the influence of a whole number of factors. The location of dry steppes, further to the South than 50º North latitude, is conductive to a great amount of solar radiation during the vegetation period. But isolation from the main mois- ture sources leads to climate aridization. Precipitation deficit increases on the background of the climate aridity [2].
Vegetable cover dynamics identification was performed in the reference area. The model field is situated three kilometers further southwest from Darkhan city within the scope of semiarid climatic zone [9]. In terms of botany and geography the field is a part of the Orkhon-Nizhny Selenginsk mountain and forest-steppe subprovince of Central Asian (Daurian-Mongolian) subregion. The territory of the province is characterized by some specifics in relation to climate, which can be explained by the location of its winter ranges Northwestern winds coming from the Asian anticyclone center on its eastern periphery, several weaken their withering influence and east sum- mer winds coming from the Pacific Ocean on the north eastern periphery moisten and temper the summer heat [3].
Some, though weakened influence Pacific monsoon. The biggest part of the area is situated in the portioned slopes
of small-altitude Orkhon-Kharaa River interfluve (absolute altitude marks 810-870 m) The model field is partially located at the eastern part of Bayan-Daba mountain foot and on the second Kharaa River terrace above the flood plain. The area is notable for its steppe, pea shrub, gramineous coldwood vegetation growing in stony, low-power, dark chestnut, farinose calcareous soils [7].
One of the methods permitting to study vegetation state and dynamics is the analysis of multi-tempo ra l satellite images. A precondition for the vegetation dynamics retrospective assessment, stimulated the researches, is the availability of the long-term history data from the Landsat satellite imagery, which have a free access via Internet in terms of Global Land Cover Facility Program (http://glovis.usgs.gov). The resolution of the images taken by scanning systems TM, ETM+ from the Landsat satellite is 30 m. These scanning systems began working after 1982. In the 1970s the system MSS functioned, its spatial resolution was 80 m, but it may not be enough for vegetation cover deciphering in terms of the large-scale mapping. The initial images have the same spectral band, moreover, they are taken approximately in the same period of vegetation development stage, because we gave a great attention to the season of shooting. It is very important to use the images of different years but approximately the same dates during the same season, otherwise there is a danger to mistake the seasonal changes for the long- term changes [5]. When identifying the vegetation dynamics we also took into account the man-made landscape changes, which require the analysis of the several multi-temporal images as well.
Table 1. Characteristics of the experimental set of satellite data
№ Satellite system and spectroradiometer Date The combination of channels
1 Landsat-8, OLI 2014 7:5:3
2 Landsat-7, ETM+ 2000 7:4:2
3 Landsat-5, TM 2010 7:4:2
4 Landsat-5, TM 1990 7:4:2
5 Landsat-4, MSS 1989 7:4:2
An automated deciphering has been carried out during the research. The Linking of the deciphered multi- temporal data for every site and an identification of the changes were performed via the software ArcGIS 10.2.1 (Fig. 1).
Fig. 1. A) The results of the automated classification of Landsat images by Isodata classification;
B) Map of vegetation Darkhan model polygon
The chosen model field of the preliminarily deciphered Landsat image 2014 shooting was mapped. A large- scale map of vegetation on this territory was created using the method of geobotanical profiles. The map legend is built on the base of ecological and geographic principles, reflecting a connection between steppes and landscape features of the territory, taking into account the phitocoenotic, floral peculiarities of vegetable cover.
The legend structure corresponds to the typological differentiation of vegetable cover. The biggest subtitles of the structure correspond to the typological criteria of the vegetation of different size, such as vegetation type, group, class, formation [8].
While mapping of the key site, both homogeneous and heterogeneous categories were identified. In this particular test site found 9 homogeneous units (feather grass, sedge et al.) and 7 heterogeneous community. Among the elementary chorologic units, microcombinations with a defined set of community, naturally repeating in the space, were found [6]. Among them there are ethers and esters complexes and combinations.
According to E.M. Lavrenko this area is characterized by the proliferation of herb-bunchgrass mainly Stipa (Stipa capilata with S. baicalensis), low-bunchgrass-herb-stipa and fescue (Festuca lenensis) steppes on dark chestnut soils, which were followed by meadow-grass and forb herbage-feather grass (Stipa baicalensis, Carex pediformis, Festuca k ryloviana) involving Pentaphylloides (Dasifora) fruticosa) steppes on mountain chernozems and grass-forb meadows steppefied (Bromopsis inermis, Carex pediformis et al.) on the meadow dark chestnut soils [7].
The map reflects the present state of vegetation cover and its horizontal structure. It is a necessary material for the monitoring of the changes in the chosen area. Almost everywhere the current vegetation cover is presented by modified communities, many of them are the stages of degradational successions, formed as a result of constant (seasonal and year-round) cattle grazing. Because of the overgrazing the vegetation of these landscapes is on the stage of middle digression. Vegetable species are in bad vital condition. General projective herbage doesn’t grow under 40%, while the average value is 15-20 %. Assessment of the species coenotic value was made basing on activity of the species. Comparative analysis of middle projective herbage showed, that 4 species have maxima l coenotic value: Carex duriuscula (C.A. Meyer), Caragana microphylla (Pall.) Lam., Artemisia frigida (Willd ), Potentilla acaulis. Their middle projective herbage is quite big (6-10 %). It is established that coenotic value of these species considerably change in the communities of different types of relief.
In the analysis of multi-temporal images for us, no doubt is of interest to offset the boundaries of comple x systems and combinations. The images in 1990 and 2010 there is a significant increase in the areas occupied by combinations of complexes and communities cereals (feather grass etc.). This is due to the fact that in these times the annual rainfall is 411 mm in 1990 and 489 mm in 2010, which greatly exceeds the characteristic of the study area. Presumably in the data during the whole vegetation was significantly better, respectively polygon modeling pastures are used less intensively, allowing indigenous communities to improve their position. In less wet periods increases the share of active-digression species (Carex duriuscula, Potentilla acaulis) and on-site Indigenous com- munities spread community featuring sedges and cinquefoil. The most stable include cold Artemisia frigida – Caragana microphylla, are also embodiments of the present digression steppes, but in this case, having a built complex with certain environmental confinement. It should be noted that participation in the communities of grasses and legumes are very few.
The received data prove the possibility to use satellite images to study natural territories. Global long-term Landsat imagery which are accumulated by the present time can be found on the free access via Internet. Moreover, they give a great opportunity to get the retrospective assessment of vegetation cover dynamics.
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