青藏高原中东部植被覆盖对水热条件的响应研究

Study on The Response of Vegetation Cover to Precipitation and Temperature in Central/East Tibetan Plateau

植被覆盖的变化常是自然因子和人类活动的综合作用.分析植被对水热条件的响应关系有助于认识人类活动在地表植被变化中的作用程度。本文旨在结合1982-2000年地面气象观测资料和NOAA卫星的AVHRR植破指数(8km),对气象站点分布相对密集的青藏高原中东部的NDVI(归一化植被指数)空间变化同水热条件的响应关系进行分析。通过水热有关指标的趋势面模拟、植被类型比较和样带分析,表明:在青藏高原中东部地区,水热条件组合较好(如常绿针叶林)或较差(如荒漠半荒漠)的区域,多年平均的NDVI旬值同水热条件的相关性不强;而范围广阔的水热条件组合中等区域(如高山草甸/草原)同水热条件相关性很高;青藏高原周边区域植被对水热条件相对不敏感.而高原主体部分植被覆盖同水热的相关性则很高(0.75以上);此外,海拔对热量条件影响很大.进而影响植被覆盖。

The Tibetan Plateau is among the few extensive regions remoted from human disturbance, and provides an ideal site to study the response of vegetation cover to water/thermal conditions （WTC）, esp. the response of natural vegetation. Therefore, this paper focuses on the spatial variation and then relations of water/thermal climate elements and NDVI （Normalized Difference Vegetation Index, AVHRR NDVI product of 8km） from year 1982 to 2000, mainly in central and east Tibetan Plateau where the gauge is basically dense enough to qualify related analyses. In the study, to investigate the relationships between spatial variation of water/thermal conditions and multi-year mean NDVI, trend surfaces of N （short for NDVI）, P （short for precipitation）, N-P relation and N-T relation are simulated, transects of four directions are designed and vegetation types are compared by group. The relation differences of N-P and N-T are respectively investigated, both spatially and biologically. According to our study, following conclusions are reached： a） Climate elements： Ten-day mean NDVI of certain region in Tibetan Plateau is influenced less by the water and thermal climate elements if the vegetation cover is evergreen dense or totally sparse. On the other hand, temperate WTC （thus vegetation cover of temperate density） tends to have stronger relationship with NDVI than extreme conditions, b） Spatial variation： As indicated by transect analysis and trend surface simulation, the relation values of peripheral Plateau are low （often because of extreme WTC and thus extreme vegetation cover） while the values of main plateau body are over 0.75 （because of temperate WTC and thus temperate vegetation cover）, c） Zonality： Since altitude plays an important role in the distribution of thermal condition in Tibetan Plateau, annual NDVI bears a abvious vertical zonality while the horizontal zonalities are not so distinct. In addition, the relations of NDVI with precipitation and temperature have no clear zonal characteristics.