Characteristics of Vegetation Cover Changes in Lantsang Basin Based on MODIS Vegetation Index Products (MOD13)
澜沧江流域植被覆盖变化特征及其与气候因子的关系

Vegetation is the important indication of regional eco-environmental characteristics. Its distribution, community structure and productivity can reflect the climate change and indicate the range of climate change. Changes of vegetation cover are mainly caused by climate change and human activities. In this paper, by comparing data characteristics of MODIS NDVI with MODIS EVI, MODIS NDVI vegetation index from 2000 to 2009 was selected to analyze characteristics of vegetation change in the Lantsang Basin. The temporal and spatial variation characteristics of NDVI and its correlation with four major climate factors (temperature, precipitation, relative humidity and sunshine duration) were analyzed. The results show that the annual average NDVI of the basin is greater than 0.45, showing a fluctuately increasing trend during 2000 and 2009; the ecological environment of the basin shows a trend of improving. Within the year, seasonal change of the average NDVI of the basin is obvious, presenting a typical unimodal distribution. The NDVI reaches the minimum value in March, begins to rise rapidly in May and reaches the maximum value in August, ranging from 0.35 to 0.60. Therefore, we know that the situation of vegetation cover also shows a trend of unimodal change in the Lantsang Basin. From June to August, the situation of vegetation cover is the best, while from February to April it is the worst. Besides, it has typical seasonal distribution characteristics, which is consistent with vegetation growth rule. The linear correlation coefficients between NDVI and the four major climate factors are 0.619, 0.691, 0.801 and -0.601 respectively. In the space, the average NDVI in the basin shows a latitudinal zonal characteristic, with the maximum value appearing in the southmost basin and the minimum value appearing in the northmost basin. During the past 10 years, the average NDVI decreased in the headstream and downstream, which mainly include Apline meadow and Typical and subtropical broad-leaved forest and increased in the Middlestream, which mainly includes shrubland. To sum up, the vegetation cover is becoming increasingly better in the Lanstang Basin, which is consistent with the conclusion obtained from the time variation perspective.