超载放牧与那曲地区高山嵩草草甸植被退化及其退化指标的探讨

对那曲地区中部高山嵩草草甸不同超载程度草地植被的调查分析结果表明,那曲地区中部高山嵩草草地超载严重,从定居点至放牧最远点,放牧压力逐渐降低,定居点附近超载高达3.73倍,超载最轻的草地也达到1.75倍;超载草地的多样性指数、植被盖度、地上现存生物量都显著低于围栏禁牧区;随超载程度的加大,莎草科植物、耐旱的杂类草、牲畜不喜食和不食的植物种有增加的趋势;综合分析超载下植被的不同特征变化并与现有的高寒草甸、草原类退化草地分类指标体系比较,初步认为,那曲地区的高山嵩草草甸都呈现退化加剧的趋势,已达到重度-中度退化程度,极重度超载区达到重度退化程度,重度和中度超载区达到中度退化程度,其比例分别达到9%和91%,远大于1996年的调查数据.

Effects of over-grazing on vegetation degradation of the Kobresia pygmaea meadow and determination of degenerative index in the Naqu Prefecture of Tibet

In this paper, the investigation and analysis of vegetation of the Kobresia pygmaea meadow under different grazing intensities was conducted in the middle region of the Naqu Prefecture. Results showed that the grasslands had suffered from over-grazing ranging from 69% to 260% in areas near residential locations. The over-grazed grasslands were shown to have a significantly lower diversity index, coverage percent, and standing biomass yield than that of enclosed grasslands which are protected from grazing. With increasing stocking rates, the number of sedge family species which are drought-resistance and inedible by livestock showed increasing numbers. Using the degenerative index based on the change in vegetation features, the K. pygmaea meadow was classified as having areas ranging from mid-level to heavy degradation, with areas showing a tendency towards further degradation. The grasslands in extremely over-grazed areas have reached the serious degradation stage and the grasslands in medium to high over-grazed areas have reached the medium degradation stage, the percentage of these stages being 9% and 91%, respectively. This figure was more severe than that recorded in 1996.