超载放牧对那曲地区高山嵩草草甸植被退化的影响

选择那曲地区中部超载严重的高山嵩草草甸为研究对象,通过对不同超载程度的草地植被调查分析,结果表明:那曲地区中部高山嵩草草地超载严重,定居点附近超载高达3.60倍,超载最轻的草地也达到1.69倍;超载草场的多样性指数、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 Kobresia pygmaea meadow in Nagqu, Tibet

In this paper, investigation and analysis of vegetation of Alpine Kobresia meadow (Kobresia pygrnaea) in different grazing densities were conducted in the middle region of Nagqu. Results showed that the grasslands of Alpine Kobresia meadow in the region have suffered from intensive grazing, over-grazing rates around the residential areas have reached 260% and the lowest over-grazing rate was also 69%. The over-grazed grasslands have significant lower diversity index, coverage percentage and standing biomass yields than those of the enclosed grasslands. With the increased stocking rates, the number of species of the Sedge family, drought-resistant weeds and grasses inedible for livestock shows an increasing trend. According to the changes in the vegetation features and compared with the classified index of degradation grasslands of Alpine Kobresia meadow, we found that the Alpine Kobresia meadow in Nagqu exhibited a degrading tendency and is in the process of heavy-to-middle level degradation. The extremely over-grazed grasslands are undergoing very serious degradation stages and the grasslands in high and medium over-grazed status are in the medium-degradation stages. The ratios have reached 9% and 91% respectively, which were more than those of 1996.