中国藏北高寒生态遥感植被变化及成因分析

 利用NOAA/AVHRR-NDVI遥感数据研究了近20年藏北高寒生态系统植被变化趋势，发现藏北植被覆盖呈现出东部高，西部低的态势；依次是农作区和森林区>高寒草甸>高寒草原>高寒荒漠草原。空间分布显示NDVI显著增加或减少的区域分布在地势比较低的东部和中部地区的森林区和高寒草甸区，在海拔较高的西部地区的高寒荒漠草原NDVI变化趋势处于轻微变化或无变化。分析造成植被变化的气候原因（温度、降水，风）和人为原因，认为不同区域植被动态变化的主导因素不同；藏北东部地区，植被变化受人类活动因素影响比较显著；中部地区，同期气候条件有所改善，植被覆盖呈增加趋势，年平均最低温度和降水对植被生长具有正效应，而风力和辐射减少引起该区植被蒸散下降也有利于植被生长。藏北地区西部为无人区，不受人类活动太大的影响，因而藏北西北部的植被变化可能更多的表现出藏北高原植被的自然变动。

Vegetation Variations and Causes in Alpine Ecosystem of the Northern Tibet Plateau Based on Remote Sensing

The spatial and temporal variations of the vegetation were investigated in the in alpine ecosystem of the Northern Tibet Plateau (NTP) using NOAA/AVHRR NDVI satellite data with 8 km spatial resolution from 1981 to 2001. The results show that significant increase and decrease of VP-NDVI occurred in the central and eastern NTP. Weak VP-NDVI dynamic appeared in the western and northwestern NTP. The relationships between Vegetation Peak-Normalized Difference Vegetation Index (VP-NDVI) and climate variables (temperature, precipitation, wind speed) were analyzed in the NTP. An obviously negative correlation between VP-NDVI and evapotranspiration was found in sub-frigid, semi-arid and frigid-arid regions of the NTP because of the decline of wind speed and solar radiation. The annual minimum temperate and precipitation have positive effect on vegetation growth in this region. In temperate humid, sub-frigid and sub-humid regions of the NTP, significant correlation between VP-NDVI and population indicates that human activities have adversely affected the grassland condition as was previously reported in the literature. Results from this research suggest that the alteration and degradation of the grassland in the lower altitude of the NTP over the last two decades of the 20th century are likely caused by variations of climate and anthropogenic activities.