The Changes Of The Vegetation Ecosystems In Tarim River Basin

Tarim River is usually considered as the lifeline of ecological environment in Xinjiang,the study on the changes of the ecological environment in it's basin had historically been a hot issue in environmental science.The status quo of the ecological environment and its multiyear changes in the Tarim River basin,and the mutual influence and connection between vegetation,soil and water in the area were clarified.This article based on MODIS-MOD13Q1 data between 2007~2017,and it took the vegetation index as entry point,in addition,used assistive software like ArcGIS and vegetation coverage estimation models.A time series model for Fractional Vegetation Cover retrieval based on multispectral remote sensing data was been established to realized the dynamic monitoring of the vegetation changes in the Tarim River basin from a macroscopic perspective.Moreover,it took the Populus euphratica as a typical vegetation representative,the effect of soil physical and chemical properties and water chemistry characteristics on the growth of Populus euphratica was illustrated from a microscopic point of view through field surveys and sampling analysis,and the suitable water and soil environmental conditions for growth and natural regeneration of Populus euphratica were investigated.It was hoped to provide the scientific basis for the protection of the natural Populus euphratica forest in the Tarim River and the ecological restoration of the watershed.The main conclusions are presented as follows:? The vegetation coverage base of Tarim River basin was low,and the spatial-temporal heterogeneity of vegetation index was large.The highest monthly vegetation index was in July,while the lowest was in March.The upper resches was the section with the highest vegetation coverage.Fractional Vegetation Cover for the core area(coastal north and south each 15 km wide)of Tarim River was 23.56% in July of 2017.In the same month,the vegetation coverage in the upstream reaches up to 3.36 times that of the downstream section;in the same reach,the annual extremum ratio of the vegetation coverage in the upper reaches was 4.28;? There was no significant difference in vegetation coverage in the whole basin between 2017 and 2007.The changes of Fractional Vegetation Cover for the main stream of the Tarim River in the summer from 2007 to 2017 was remarkably rising,but in the autumn it's growth was not significant.Time series model made a good prediction for the future vegetation restoration trend of the Tarim River,mainly reflecting in the following two stages: the first stage is the improvement of the vegetation index in autumn,and the second stage is the vegetation index remaining stable in autumn and gradually increased in summer;? Dynamic monitoring and quantitative analysis of vegetation restoration effectiveness based on EVI index is feasible.Through the analysed of variance between NDVI and EVI in 2017 from the same satellite and in the same time and area,there was no significant difference between them.But in practical applications,NDVI tended to be low in areas with low vegetation coverage or in dormant and late growing seasons,while it tended to be high in areas with high vegetation coverage or in early growing seasons;? Hydrochemical characteristics in the Tarim River Basin could only maintain the survival of the existing aged Populus euphratica,and only suitable for seeding and germination of the trees in the narrow area near the river.Large-scale agricultural production activities in the region have caused the pollution of surface water.Soil texture powder and sand,low organic matter content(0.33%~0.80%),high salt content(0.42%~6.28%)and high pH value(7.83~8.46)restricted the renewal and rejuvenation of Populus euphratica.The high pH value was the main factor that inhibits the growth of Populus euphratica among them,since Populus euphratica was suitabled for growth in loamy soils by the river coast with pH of less than 8;? Subject to natural factors and human factors such as deforestation,overgrazing and overgrazing,the natural regeneration of Populus euphratica along the Tarim River was faceing difficulties.Not only that,the survival rate of afforestation was low.In order to restore the degraded ecosytem in Tarim River basin,the establishment of the enclosed and forbidden reserves of desertified land and the technology of sand control with low coverage are effective method.