雅鲁藏布江流域植被格局与NDVI分布的空间响应

雅鲁藏布江流域海拔高差约达7 000 m,气候条件复杂、生态系统类型多样,植被格局空间变化显著.笔者基于1:100万植被类型图、SPOT_VEGETATION NDVI数据集和数字高程模型(DEM),综合运用GIS空间分析技术,提取与定量分析了流域主要植被类型、空间分布特征,并结合海拔梯度、气候条件变化探讨了流域植被格局与NDVI空间变化的耦合关系.结果表明:(1) 雅鲁藏布江流域植被类型包括针叶林、阔叶林、灌丛、荒漠、草原、草丛、草甸、高山植被等11个植被型组,21个植被型,其中米林宽谷的植被型最多,自下游至上游的山南宽谷、日喀则宽谷及马泉河宽谷随着海拔梯度的变化,植被类型多样性总体呈下降趋势.(2) 随着海拔的增加,植被型组和植被型的个数均呈先增大后减小的趋势,以海拔3000～4 000 m和4 000～5 000 m最多,流域植被格局的垂直地带性显著.(3) 流域植被格局与NDVI变化表现出较好的空间一致性.针叶林、阔叶林和草丛等3个植被型组的NDVI值均以10-12月最大,其余8个植被型组的NDVI值均以7-9月最大、1-3月最小.海拔3 000 m是流域尺度植被格局变化的一个转折点.

Vegetation Pattern and Spatial Distribution of NDVI in the Yarlung Zangbo River Basin of China

The range of elevation is over 7 000 meters a.s.l. in the Yarlung Zangbo River Basin, where climate conditions are very complex and types of ecosystem are diverse, the spatial pattern of vegetation distribution changes greatly. Based on 1:1 000 000 vegetation map, SPOT_VEGETATION NDVI data sets and digital elevation model (DEM), the dominant vegetation types and theirs spatial distribution in the basin were extracted and analyzed quantitatively with the help of Geographical Information System (GIS). Thereafter, combined with the elevation gradients and climate conditions in different wide valley sections of the basin, we discussed therelationship between vegetation pattern and spatialdistribution of NDVI. (1) There are 11 vegetation type groups (including coniferous forest, broad-leaved forest, bush, desert, grassland, meadow, alpine vegetation, etc.) and 25 vegetation types in the basin. The numbers of vegetation types in the Milin wide valley are the most, while the diversity of vegetation types among Shannan wide valley, Shigatse wide valley and Maquanhe wide valley showed a decrease trend totally from downstream to upstream. (2) The numbers of vegetation type groups and vegetation types both increase at first, and then decreased with the increase of altitude, of which, 3000-4 000 m and 4 000-5 000 m are the most, the vertical zonality of vegetation pattern in the basin is remarkable. (3) The spatial consistency between vegetation pattern and NDVI change isgood in the basin. The greatest NDVI value of coniferous forest, broad-leaved forest and grass vegetation are all in October-December, while the greatest and the least NDVI value of the other 8 vegetation type groups were all in July-September and January-March, respectively. The altitude of 3 000 m is a turning point at which vegetation pattern on the basin scale ofthe Yarlung Zangbo River change significantly.