| Vegetation is the basis of the existence and development of the ecosystem,which can reflect the changes of the ecological environment to a certain extent.As the core component of ecological environment,vegetation also plays an important role in climate regulation and soil and water conservation.The western sichuan plateau is not only an important water conservation area and a typical ecologically fragile area in China,but also an important area for the implementation of ecological environment protection and construction.Therefore,in-depth study of the impact of climate change and human activities on the dynamic changes of vegetation coverage is the key to understanding the mechanism of vegetation degradation and controlling vegetation degradation,which is of great significance to the formulation and implementation of sustainable development strategies for the ecological environment in this erea.Based on the MODIS-NDVI vegetation index product and climate data from 2000 to 2017,this paper evaluates the dynamic changes of FVC(fractional vegetation cover)in the study area from the time and space perspectives by using the methods of cell dichotomy model,linear regression model,Hurst index(R/S rescaled range analysis method),correlation analysis,residual trend analysis,and so on.The relationship between chemistry and climate change,human activities to explore the driving factors of FVC dynamic change.The results showed that:(1)Vegetation coverage in the western Sichuan Plateau has generally performed well.The FVC value showed a slight increase in fluctuation from 2000 to 2017.The interannual change trend was obvious,with a growth rate of 2.4% / 10 a.The geometric characteristics of the annual variation curve of FVC in different elevation ranges are similar,but the variation amplitude and anomaly variation rate are slightly different.The FVC in the study area showed a gradual decreasing trend from northeast to southwest in space.The areas with better vegetation coverage are mainly located in the northeast of the western Sichuan plateau,while the areas with worse vegetation coverage are concentrated in Dege County,Ganzi County,Litang County,and Luding County.And in the area of Xiaojin County,in the central and southern parts of the western Sichuan plateau,FVC values are characterized by the distribution of north-south ditch belts,showing a trend of decreasing in the middle to the ditch belt regions at both ends.(2)The area of the western Sichuan Plateau where FVC is increasing is significantly higher than that of the decreasing area.The increasing areas are mainly distributed in Ruoergai County,Hongyuan County,Jiuzhaigou County and Mao County;the decreasing areas are mainly distributed In Shiqu County,Wenchuan County,Kangding City and other places,Shiqu County and Wenchuan County are the most significant.The reverse persistent feature of vegetation change is stronger than the positive persistent feature,and the vegetation coverage will improve in most areas in the future.Among them,areas that continued to improve slightly and continued to improve significantly accounted for 9.42% and 2.56%,respectively,and those that improved from degradation accounted for 43.32%.(3)The response of FVC to climate change in the western Sichuan Plateau has a significant time lag.The annual average FVC of vegetation has a positive correlation with the temperature and precipitation in four different periods(May-September,April-August,March-July,February-June).The correlation coefficient with the temperature during the same period is the largest(P ?0.01),while the FVC and the cumulative precipitation show a month lag.As a whole,FVC and climatic factors in this region have a strong positive correlation,in which FVC responds more strongly to temperature than to precipitation.(4)The response of FVC to climatic factors in the study area is mainly positively correlated.The impact of precipitation on vegetation growth is wider and the promotion effect is more obvious,while the temperature impact on vegetation growth is relatively concentrated,and it is scattered in Aba County.Around Hongyuan County.FVC in the western Sichuan Plateau is weakly affected by the combined effects of average temperature and accumulated precipitation,and there are complementary phenomena of positive and negative correlations in some regions.The difference in complex correlation between FVC and climatic factors in the study area is related to the altitude and vegetation type in the area.(5)FVC in most areas of the western Sichuan Plateau is driven by non-climatic factors.The area of the area affected by non-climate factors(including human activities,natural disasters,etc.)is 95.85%,mainly located in the southeast and southwestern parts of the country;the area of the area affected by climatic factors is only 4.15 of the area of the study area %,Of which 1.66% are driven by strong temperature,1.18% are driven by precipitation,0.39% are driven negatively by temperature and precipitation,and 0.39% are driven by strong temperature and precipitation.They respectively accounted for 1.18% and 0.07% of the total area.(6)The vegetation cover in the western Sichuan Plateau is gradually strengthened from west to east due to the impact of climate change,and the area of positive impact(contribution)is slightly larger than the negative impact(contribution);the value of the contribution rate of human activities has the most severe negative impact on FVC in the northwest direction(human Activity contribution rate > 60%),while showing a strong positive impact in the southwest direction(human activity contribution rate > 80%);the interaction of climate change and human activity promotes the reduction of FVC in a larger area,about It is more than 60%,indicating that the interaction of climate change and human activities is the main driving force for the change of vegetation cover in the western Sichuan Plateau. |
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