Temporal And Spatial Variation Of Vegetation Cover And Its Influencing Factors In The Southwest Tibetan Plateau From 2000 To 2020

As an important component of terrestrial ecosystems,vegetation plays an important role in maintaining ecological balance and economic development at regional and global scales.The Qinghai-Tibet Plateau has a complex and diverse vegetation type,a fragile and sensitive ecological environment,and is highly susceptible to the influence of external factors such as climate change and human activities.It is important to investigate the dynamic change pattern of local vegetation,the interrelationship between natural factors and human activities and vegetation,which is of scientific and practical significance to grasp the status of regional ecosystems,maintain the balance of ecosystems and promote the sustainable development of ecosystems.Located in the southwestern part of the Tibetan Plateau,the Southwestern Tibetan Plateau(SWTP)is the transportation choke point between China and Bhutan,India,Nepal and other countries,as well as the origin of several international rivers,and has an important value of water conservation and ecological barrier.In recent years,under the combined influence of climate change and human activities,ecological problems such as glacier retreat,grassland degradation and desertification have been intensifying aggravated,and are facing enormous pressure on agricultural and pastoral production and ecological protection and socio-economic development.Taking the SWTP as an example,this paper analyzes the pattern of vegetation cover change from 2000 to 2020 based on long time series of remote sensing images,meteorological,topographic and social statistics data,and reveals the influence of climatic factors temperature,precipitation,topography,population,economy and grazing behavior on vegetation cover change through various methods such as correlation analysis,residual analysis and topographic distribution index;Based on the results of the analysis of the main driving factors,the influencing factors of vegetation cover are classified and control measures for sustainable development of the region are proposed.The main conclusions are as follows:(1)Over the past 20 years,the vegetation cover in the SWTP has obvious temporal and spatial differentiation and dynamic change.Since 2000,The NDVI of the SWTP has been increasing at different rates,with the NDVI has been increasing from northwest to southeast throughout the year,seasonally and monthly.The degraded areas are mainly distributed in counties with pure animal husbandry and semi-agricultural and semi-pastoral areas.The NDVI in the study area as a whole is increasing and locally decreasing,among which the areas with decreasing NDVI are mainly distributed in pastoral and semi-agricultural and semi-pastoral counties.(2)The change of temperature and precipitation on the SWTP are significantly and positively correlated with NDVI.Over the past 20 years,the annual average temperature of the SWTP has been warming at a rate of 0.66?/10 a,with a low in the west and a high in the east;the annual average precipitation has a fluctating trend,with a low in the northwest and high in the southeast.The NDVI and annual average temperature and annual average precipitation in the study area are positively correlated,among which the partial correlation coefficient with the annual average temperature is high in the west and low in the east,and the partial correlation coefficient with the annual average precipitation shows a spatial characteristic of low in the middle and high in the surroundings,and the complex correlation shows a distribution pattern of low in the middle and high in the surroundings.(3)The mean NDVI value and vegetation cover changes on the SWTP were mainly affected by altitude and slope.The mean NDVI value in the study area decreased with the increase of the altitude,and the significant decrease was mainly distributed in the area with the altitude of 4000-5000 m,while the significant increase was mainly distributed in the area with the altitude of 4500-5000 m.The mean NDVI value increased with the increase of slope,and the significant decrease and increase were mainly distributed in flat slope,gentle slope and steep slope.Slope direction had no significant effect on NDVI and vegetation change types.There were significant differences in vegetation change types within the distribution range of comprehensive topographic factors.Among the 363 topographic combinations of elevation,slope and aspect,230 of them were the dominant topographic combinations in the study area.(4)Over the past 20 years,the population density and Real GDP per capita in the SWTP have shown a significant increase,with an average increase of 22.93people/km2 and 354,300 yuan per decade.The population density gradually increased from west to east,and the Real GDP per capita showed the distributed characteristic of high in the west and low in the east.NDVI was positively correlated with population density and Real GDP per capita.Over the past 20 years,the number of livestock and grazing intensity both showed a significant decreasing trend,with an average decrease of 1.6717 million sheep and 2.37 head/ha per decade,the number of livestock showed the distribution characteristics of the low in the west and high in the east,high in the north and low in the south,grazing intensity showed the distribution characteristics of low in the west and high in the east,and NDVI was negatively correlated with the number of livestock and grazing intensity.(5)The combined effect of climate change and human activities on the SWTP is the main reason cause of NDVI changes.In the past 20 years,the NDVI residual values in the study area increased overall and decreased locally.In the study area,the contribution of single climate change to NDVI changes was positive in 57.41% of the regions,and the contribution of single human activities to NDVI changes was positive in 69.22% of the regions.62.86% of the regions were affected by the combined effect of climate change and human activities,among which 51.20% were affected by a combination of climate change and human activities resulting in an increase,and11.66% had a decrease in NDVI.(6)The SWTP including vegetation improvement(degradation)caused by climate and grazing,vegetation improvement(degradation)caused by climate and non-grazing,vegetation improvement(degradation)caused by climate,vegetation improvement(degradation)caused by grazing,vegetation improvement(degradation)caused by non-grazing and no obvious trend,etc.6 classes.Based on the spatio-temporal changes of vegetation cover and its main influencing factors,and taking into account the needs of ecological civilization construction and economic development,we propose management suggestions and countermeasures to maintain the sustainable development of ecological environment,starting from the priority of protection and maintaining the integrity and function of natural ecosystem: continue to implement ecological projects,maintain the stability of ecological environment,enhance the resilience of ecosystem and its adaptability,and explore a sustainable development path of ecological environmental protection and social and economic maximization.To explore a sustainable development path that maximizes ecological environmental protection and social economy,and to promote the mutual promotion and synergistic development of social,economic and ecological systems.