The Dynamic Change Of Landscape Pattern Of Vegetation Coverage In Western Sichuan Plateau

Vegetation is the most sensitive factor in terrestrial ecosystem.The Western Sichuan Plateau,located in the west of Sichuan Province,has a high altitude.It is located in the middle and upper reaches of the Yangtze River in the ecological barrier area.Because of its complex terrain structure,the surface ecological environment of the West Sichuan Plateau is very fragile.Vegetation is an important factor to maintain the ecological system in the Western Sichuan Plateau.The change of vegetation landscape pattern will have a significant influence on the climate and water resources in the Western Sichuan Plateau,and thus cause the ecological environment deterioration.Therefore,it is of great significance to the monitoring and protection of vegetation resources and water resources and the construction of the ecological environment by analyzing the landscape pattern evolution and influencing factors of the vegetation coverage in the Western Sichuan Plateau.This study took the Western Sichuan Plateau as the research area,mainly using the MODIS NDVI data of 2000-2016 years to study the landscape pattern evolution of vegetation coverage in the Western Sichuan Plateau and its influencing factors.First,based on the pixel two model,the vegetation coverage of Western Sichuan Plateau was estimated and classified.Secondly,the landscape pattern changes of the vegetation coverage in Western Sichuan Plateau were analyzed by the trend analysis method,transfer matrix method,dynamic degree analysis method,center of gravity transfer method and landscape pattern index method.Finally,correlation analysis is used to analyze the correlation between vegetation coverage change and climatic factors and terrain factors in Western Sichuan Plateau.The main conclusions of this study are as follows:(1)the change of vegetation coverage.The vegetation coverage of Western Sichuan Plateau was higher in the past 2000-2016 years,and the change of vegetation coverage was not significant,and the change trend remained unchanged.The vegetation coverage area of the middle vegetation was changed greatly,and the vegetation coverage area of the other grades changed little;The coverage of low vegetation,middle and low vegetation,middle vegetation and middle and high vegetation mainly evolves in the direction of evolution,The high vegetation coverage mainly evolves to the degenerate direction;The absolute dynamic degree of vegetation coverage is small,the relative dynamic degree is larger,the dynamic change of middle vegetation coverage is the most intense,but the overall annual change rate of vegetation coverage is not large.The center of gravity of the vegetation coverage of each grade is little offset,and the gravity center of high vegetation coverage tends to be in the northeast,and the other vegetation coverage is in the southwest.(2)the evolution of landscape pattern.On the landscape level,the degree of landscape fragmentation in the Western Sichuan Plateau is increasing,but the overall change is not large,the intensity of the landscape anti-interference is enhanced,and the patch shape in the landscape has a complicated trend,but the development is slow,and the landscape is developed to diversity and uniformity,and the connectivity is poor.On the level of plaque,the degree of landscape fragmentation of middle vegetation coverage and middle and high vegetation coverage in Western Sichuan Plateau is higher.Compared with low vegetation,middle and low vegetation and middle vegetation coverage,middle and high vegetation and high vegetation coverage are more capable of resisting environmental change,middle and high vegetation coverage degree is high,middle vegetation and middle and high vegetation coverage is the most complex.Vegetation coverage gradually increased to high vegetation coverage.(3)climate.The overall annual average temperature of the Western Sichuan Plateau is low and the temperature change is more stable.There is not a significant positive correlation between annual mean temperature and annual vegetation coverage.The area of positive correlation in the whole study area accounted for 61.04%,the non significant positive correlation accounted for 56.40%,the negative correlation area accounted for 38.96%,the non significant negative correlation accounted for 37.76%,and the distribution was more scattered.The annual average precipitation distribution in the Western Sichuan Plateau is uneven,the annual average precipitation is fluctuating and descending,and the decline is not significant;there is no significant correlation between annual precipitation and annual vegetation coverage;the area of positive correlation in the whole study area accounted for 59.35%,the non significant positive correlation accounted for 56.00%,the negative correlation area accounted for 40.65%,the non significant negative correlation accounted for 39.43%.(4)terrain.The low vegetation coverage in Western Sichuan Plateau is mainly located in high altitude area,the coverage of vegetation in 3500-4000 m is high.With the elevation of altitude,the vegetation coverage gradually decreases,and the vegetation coverage area of each grade increases first and then decreases with the increase of grade grade,and the area of each grade is mainly middle and high vegetation and high vegetation coverage.Middle and high vegetation coverage in the area of 0-15 degree is most,high vegetation coverage over 15 degrees is most;The area of each vegetation coverage is smaller on the slope without slope.The vegetation coverage is smaller in the non slope upward area.