藏西北高寒牧区草地退化现状与机理分析

以藏西北高寒牧区为研究区域,综合利用NOAA、MODIS卫星NDVI(归一化植被指数)、气象资料、社会统计资料并结合GIS技术,对藏西北高寒牧区的草地状况和退化机理作了分析。结果表明:①藏西北高寒牧区草地覆盖度等级呈正态分布,且中等偏下略多,地表植被总体上比较稀疏;②2005年区域内的草地退化总面积为14.19×10⁴km²,占区域天然草地总面积的39.64%,其中轻度退化面积最多,占退化总面积的65.96%,其次是中度和重度退化,分别占25.20%和8.84%;③草地退化的主要原因一是与近年来该区域的气候变化有关,二是草地超载率达到59.18%,过度放牧引起的草地退化和沙化现象也越来越严重,是局部草地退化的根本原因,人口的增加和人类活动频繁对草场的破坏,也是近年来草地退化的主要原因。

Analysis of the Situation of Grassland Degradation and It's Mechanism of the Alpine Pastoral Area in Northwestern Tibet

Lying between 80.33°-94.93°E and 28.76°-36.49°N, the alpine pastoral area of northwestern Tibet is known as the ridge of the roof of world with a mean elevation of 4500 m. As an alpine pastoral area, the animal husbandry faces the dual pressures of both gaining the yield and protecting the pasture. The environmental condition of this area has significant effect on the main rivers, climate and eco-environment of Tibet and the whole country, even on the globe for its rigorous natural condition and fragile ecosystem.This study selected vegetation cover as the main evaluation index, and analyzed the present situation of grassland degradation and it’s mechanism of the alpine pastoral area in northwestern Tibet, based on the remote sensing data such as NDVI data derived from NOAA/AVHRR with a spatial resolution of 1 km of 1992-2005 and from MODIS with a spatial resolution of 0.5 km of 2002-2005 respectively in this area, in combination with investigation data of the actual condition of grassland resources completed according to the background material of the end of the 1980’s. The grassland degradation processes and their response to climate change during 1971-2005 were discussed and analyzed systematically in the study using meteorological data.The results show that grassland coverage rank degree presents normal distribution with ground vegetation being sparse as a whole in this region. According to the present degenerated situation, the total degenerated grassland area is 14.19×10⁴km² , occupying 39.64% of the region’s total natural pasture area. Of which light degenerated area is most extensive, being 65.96%, moderate and heavy degenerated areas are 25.20% and 8.84% respectively of the total degenerated grassland area.From the analysis, we can conclude that the direct factors related to grassland degeneration in the study area are climate change for the annual temperature increasing with cess precipitation in recent years in Naqu county. The indirect factors are over-grazing and human activities. For example, the overload rate reaches 59.18% as a result of domestic animal’s massive increase, thus bringing increasing pressure on part of pasture, and causing grassland degeneration and more and more serious desertification phenomenon. In addition, population increase and frequent human activities also bring serious damage to the grassland.