1982~2013年青藏高原高寒草地覆盖变化及与气候之间的关系

利用GIMMS NDVI数据和地面气象站台观测数据,对青藏高原1982~2013年高寒草地覆盖时空变化及其对气象因素的响应进行研究,结果表明：青藏高原高寒草地生长季NDVI表现为从东南到西北逐渐减少的趋势,近32 a来,整个高原草地生长季NDVI呈上升趋势,增加速率为0.000 3/a (p<0.05);高寒草地生长季NDVI年际变化具有空间异质性,整体为增加趋势,呈增加趋势的面积约占研究区域面积的75.3%,其中显著增加的占26.0% （p<0.05）,类型主要为分布在青藏高原东北部地区的高寒草甸;比例为4.7%,草地类型主要为高寒草原,主要分布在高原西部地区;基于生态地理分区的分析显示,青藏高原草地与降水、温度的相关关系具有明显的空间差异,高寒草地生长季NDVI均值与降水呈显著正相关,对降水的滞后效应显著;高原东北部温度较高,热量条件较好,降水为高寒草地生长季NDVI变化的主导因子;东中部地区降水充沛,温度则为高寒草地生长的制约因子;南部地区降水和温度都较适宜,均与高寒草地生长季NDVI相关性显著(p< 0.05),共同作用于草地的生长;中部和西部地区,气候因子与高寒草地生长季NDVI关系均不显著。

Variations in Alpine Grassland Cover and Its Correlation with Climate Variables on the Qinghai-Tibet Plateau in 1982-2013

The response of structure and function of terrestrial ecosystem to global climate change has become a major point. Vegetation is an essential component of the terrestrial ecosystem which has proved to be sensitive to climate change. Normalized Difference Vegetation Index (NDVI) is widely recognized as a good indicator of vegetation coverage and productivity, has been widely used to indicate vegetation activity and dynamics, also vegetation growth, ecosystem structure and functions respond to climate change. Climate warming has important influence on the vegetation coverage, and alpine grassland is one of the most significant vegetation type on the Qinghai-Tibet Plateau. This study used GIMMS NDVI data sets and climate data from 40 meteorological stations to investigate spatial and temporal variations of alpine grassland cover and the response of NDVI to climatic variables on the Qinghai-Tibet Plateau in 1982-2013. The results showed that the average growing season NDVI is high in the southeast and low in the northwest. As a whole, the alpine grassland cover tended to increase on the Qinghai-Tibet Plateau, with the rate of 0.000 3/a (p<0.05) in the past 32 years. Spatially, the tendency of alpine grassland NDVI showed great heterogeneity, with the significantly NDVI increased mainly distributed in the northeastern part of Qinghai-Tibet Plateau dominated by alpine meadow which approximates to 26.0% (p<0.05) of the total study area. The area with significantly decreased area accounted for 4.7%, mainly emerged in the western part where the grassland was dominated by alpine steppe. In the regional scale, the variation in alpine grassland cover was more closely related to precipitation than other climate factors. The spatial characteristics of the relationship between growing season NDVI and climatic variables were analyzed based on the eco-geographical regions. Significant lagged correlations between precipitation and seasonal NDVI were found for the alpine steppe. The results suggested that precipitation was the key limit variable in the northeastern part of Qinghai-Tibet Plateau with higher annual mean temperature. But in the eastern and central eco-regions with the more rainfall, temperature could limit the growth of grassland vegetation. In the southern plateau with more precipitation and higher temperature compared with other regions, the correlations between alpine grassland cover and climatic factors were significant positive. The change of alpine grassland cover was not significantly relevant to climatic variables in the middle and western part of Qinghai-Tibet Plateau.