Spatial-temporal Changes Of Vegetation Index And Responses To Regional Temperature In The Northern And The Southern Regions Of Qinling Mountains During The Past 30 Years

As the supreme mountains on the east of orient, Qinling Mountains are not only the important demarcation line of China's North and South, but also the water south of the middle route of South-to North Water Divertion. In terms of the analysis methods of MVC, regression, correlation and wavelet etc., the temporal & spatial characteristics of vegetation cover variations and the relationship between the climate were analyzed based on the longer term GIMMS (1981.7-2003.12)and SPOT VEGETATION(1998.4-2007.10) NDVI data.The studies of vegetation cover variation and its responses to regional climate change had been carried out. The main conclusions included:(1) The spatial-temporal changes of vegetation in the northern and the southern regions of Qinling MountainsThe seasonal NDVI of the northern and the southern regions of Qinling Mountains fluctuated with the same trends as time passed; In winter and autumn, the seasonal NDVI of the two regions were increased with the time, while they were decreased in spring and winter.The vegetation coverage in two regions were all reduced during the past 30 years, and the speed of the reduction in the northern part was greater than that of the southern part. Before 1998, there were small changes of vegetation, but it became decreased because of the climate change after 1998, and presented the minimum value in 2000.(2) Responses of vegetation coverage to regional environment change in the northern and the southern of Qinling MountainsThe climate in the northern and the southern of Qinling Mountains are becoming warm and dry during the past 30 years, and the differences of temperature and precipitation between the two regions were getting smaller. In the southern part of Qinling Mountains, the impact of temperature on vegetation cover lagged for 1 month, but the impact was small in the northern region because of human activities. At the same time, the rainfall is relatively abundant in the two regions so that its impact was less than that of temperature. Correlation analysis showed that the seasonal mean NDVI in spring and summer were tightly correlated with temperature for both regions during 1982 to 1997. But after 1998, temperature was insignificant with either annual NDVI or seasonal NDVI at any time, except winter in the northern region, when the correlation coefficient of winter's NDVI to temperature in the Northern Qinling Mountains was as high as 0.75 (P<0.05), which represented an important signal of regional ecological response to global warming.(3) Responses of vegetation change to temperature in the southern region of Qinling Mountains during the past decadesDuring the past decades, the pixels where NDVImax significantly decreased account for more than 15% of the total pixels in the southern region of Qinling Mountains, and the NDVI in the partial broad-leaved forest-distrubted area reduced significantly. The most degraded vegetation were shrubs and bushes.The annual maximum of NDVI was correlated significantly with the mean air temperature calculated from last August to July, and the correlation followed by significant positive, insignificant positive and Significant negative from north to south in the southern region of Qinling Mountains. What's more, there may be two sensitivity thresholds of positive and negative correlation, which means that when the temperature is lower than 13.0±0.2℃, it is significantly positive correlated with the NDVImax, while it will reduce the NDVImax when it higher than 14.4±0.2℃. So it was important to returning farmland to forest and grassland, especially in the southern part of the region.