青藏高原草地植被覆盖变化及其与气候因子的关系

VARIATIONS IN GRASSLAND VEGETATION COVER IN RELATION TO CLIMATIC FACTORS ON THE TIBETAN PLATEAU

为揭示气候变化对青藏高原草地生态系统的影响及其生态适应机制，利用1982～1999年间的NOAA／AVHRR NDVI数据和对应的气候资料，研究了近20年来青藏高原草地植被覆盖变化及其与气候因子的关系。结果表明，18年来研究区生长季NDVI显著增加（P=0．015），其增加率和增加量分别为0．41％a^-1和0．0010a^-1。生长季提前和生长季生长加速是青藏高原草地植被生长季NDVI增加的主要原因。春季为NDVI增加率和增加量最大的季节，其增加率和增加量分别为0．92％a^-1和0．0014a^-1；夏季NDVI的增加对生长季NDVI增加的贡献相对较小，其增加率和增加量分别为0．37％a^-1和0．0010a^-1。3种草地（高寒草甸、高寒草原、温性草原）春季NDVI均显著增加（P〈0．01；P=0．001；P=0．002）；高寒草甸夏季NDVI显著增加（P=0．027），而高寒草原和温性草原夏季NDVI呈增加趋势，但都不显著（P=0．106；P=0．087）；3种草地秋季NDVI则没有明显的变化趋势（P=0．585：P=0．461；P=0．143）。3种草地春季NDVI的增加是由春季温度上升所致。高寒草地（高寒草甸和高寒草原）夏季NDVI的增加是夏季温度和春季降水共同作用的结果。温性草原夏季NDVI变化与气候因子并没有表现出显著的相关关系。高寒草地植被生长对气候变化的响应存在滞后效应。

To advance our understanding of the effects of climate change on grassland ecosystems, we used a time series （ 1982 - 1999） data set of the Normalized Difference Vegetation Index （NDVI） together with historical climate data to analyze interannual variations in grassland vegetation cover and explore the relationships between NDVI and climatic factors on the grasslands of the Tibetan Plateau. The NDVI increased significantly by a ratio of 0.41% a^-1 and a magnitude of 0.001 0 a^-1 during the growing season （p =0.015）. An increase in NDVI during the growing season resulted from both the advanced growing season and accelerated vegetation activity. The largest NDVI increase was in the spring with a ratio of 0.92% a^-1 and a magnitude of 0.001 4 a^-1. The NDVI increase in the summer was a secondary contributor to the NDVI increase during the growing season with a ratio of 0.37% a^-1 and a magnitude of 0.001 0 a^-1. In the spring, the NDVI increased significantly in the alpine grasslands （alpine meadow and alpine steppe） and temperate steppe （p 〈 0.01; p = 0.001; p = 0.002）. During the summer, a significant NDVI increase was found in alpine meadows （p = 0.027）. However, the NDVI increase in alpine and temperate steppe was not significant （p = 0. 106; p =0.087）. In the autumn, no significant increase was found in the three grasslands （p = 0.585; p = 0.461; p =0.143）. In the spring, the NDVI increase in three grasslands was corresponded to an increase in temperature. In the summer, the NDVI was related to temperature and sensitive to precipitation in the spring in the alpine grasslands （alpine meadow and alpine steppe）. However, no significant statistical relationship was found between NDVI and climatic factors in temperate steppe. Significant lagged correlations between precipitation and NDVI were found for alpine grasslands （alpine meadow, alpine steooe）.