Vegetation Cover Change Analysis Of National Key Ecological Function Areas In Northwest China After The Implementation Of Ecological Projects

Since 2000,China has implemented a large number of ecological projects in the northwest region.Vegetation construction is an important part of the implementation of ecological projects.The key ecological function areas in the northwest have played important roles in the protection of ecological environment,and are also the key areas for the implementation of ecological projects.It is important to understand the vegetation change and the corresponding driving factors since the implementation of the ecological projects.Data used in this paper including MODIS NDVI data with 250 m spatial resolution in northwest China,the daily meteorological data of 76 meteorological stations,statistical data and land use data.The methods used in the paper mainly including trend analysis,partial least squares regression,Standardized precipitation and evapotranspiration indices(SPEI).In order to provide basis for the ecological construction and vegetation protection,we analyzed the characteristics of vegetation cover changes during the growing season of key ecological function areas in the northwestern China from 2000 to 2015,the driving factors of vegetation cover change in the growing season and the sensitivity of vegetation during different growth stages to climate change.The following conclusions are drawn from the study:(1)At the regional scale,the growing season NDVI of the key ecological function areas in northwest China all showed an increasing trend from 2000 to 2015.The growing season NDVI in Gannan area,Qilian Mountain area,Qinba Mountain area,Loess Plateau area,Tarim area,and Alkin area showed a significant increase(P<0.01).In the areas with significant increasing rate,the increasing rate in the Loess Plateau area was the fastest,at 0.095/10a;increasing rate in Alkin area was the slowest,at 0.016/10 a.Growing season NDVI in Altai Mountain area,Sanjiangyuan area and Yinshan Mountain area all showed a non-significantly increasing trend,with the rate of 0.006/10 a,0.01/10 a and 0.016/10 a respectively.(2)At pixel scale,the proportion of increasing trend pixels are the highest of all the key ecological function areas in northwest China from 2000 to 2015.In Gannan area,Qilian Mountain area,Qinba Mountain area,Loess Plateau area,and Alkin area,more than 90% pixels showed an increasing trend.The increasing trend of NDVI in Loess Plateau area was most significant,99.56% of the pixels showed an increasing trend,and 84.26% of the pixels in the whole area were extremely significant(p<0.01).(3)The partial least squares regression model in the paper has different accumulative explanatory capacity for the changes of growing season NDVI in different areas.Except for Sanjiangyuan area,the cumulative explanatory capacity of the partial least squares regression model in other areas are greater than 0.5.Explanatory capacity of the model in Loess Plateau is the biggest at 0.89.(4)Expect for Gannan area and Qinba Mountain area,the climate factors have significant or moderate explanatory capacity for the other areas.Temperature has significant explanatory capacity for the changes of growing season NDVI in Sanjiangyuan area.Growing season precipitation has significant explanatory capacity for the growing season NDVI in Altai Mountain area and Yinshan Mountain area,which is moderate in Sanjiangyuan area,Qilian mountain area,Loess Plateau area,Tarim area and Alkin area.Growing season SPEI has significant explanatory capacity for the change of growing season NDVI in Altai Mountain area,Loess Plateau area and Yinshan Mountain area,which is moderate in Tarim area and Alkin area.(5)The accumulative afforestation area has significant or moderate impact on the areas except for Altai Mountain area and Yinshan Mountain area.The accumulative afforestation area has moderate impact on Sanjiangyuan area,which is significant in Gannan area,Tarim area and Alkin area.The number of livestock has moderate explanatory capacity for the NDVI change in Alkin area.The change of cultivated area has significant explanatory capacity in Sanjiangyuan area,which is moderate in Gannan area and Qinba Mountain area.(6)The key ecological fuction areas can be divided into four categories.Firstly,the areas with significantly vegetation increase,promoted by ecological engineering and climatic factors,including Qilian mountain area,Loess Plateau area,Tarim area and Alkin area.Secondly,the areas with significantly vegetation increase,mainly promoted by ecological engineering,including Gannan area and Qinba Mountain area.Thirdly,the areas with vegetation increase,which not significant,mainly affected by climatic factors and ecological engineering,including Sanjiangyuan area.Fourthly,the areas with vegetation increase,which not significant,mainly affected by climatic factors,including Altai Mountain area and Yinshan Mountain area.(7)The sensitivity of vegetation growth to climate change is different in different ecological function areas.For the sensitive month of vegetation growth to climate change,Altai Mountain area,Qinba Mountain area and Tarim area are May,Gannan area and Alkin area are July,Yinshan Mountain area is June,mainly influential factors of these areas are precipitation and SPEI.In August,vegetation in Sanjiangyuan is most sensitive to climate change,affected by the common positive effects of temperature,precipitation and SPEI.Vegetation in Qilian Mountain area is most sensitive to climate change in April,mainly affected by positive affects of temperature and precipitation.In July,vegetation in Loess Plateau area is most sensitive to climate change,controlled by the negative effect of temperature and the positive effect of SPEI.