在青藏高原中国科学院海北高寒草甸生态系统定位研究站对金露梅高寒灌丛草场植被开展了长期不同放牧强度试验,分别在短期(4年)、中期(11年)和长期(18年)放牧阶段研究不同放牧干扰强度对草地植物物种多样性、群落结构、地上生物量和草场质量的影响.研究表明,在不同放牧阶段,随着放牧强度增加植物群落的高度和盖度都降低.在中期放牧干扰阶段,物种多样性数和均匀度指数随着放牧强度增加呈现典型的单峰曲线模式;在长期放牧干扰阶段,随着放牧强度增加,占优势地位的灌木和禾草被典型杂类草替代,其中的重度放牧干扰简化了高寒灌丛植被群落结构,减少了地上现存生物量,特别是可食优良牧草生物量.植被对放牧的响应除了与放牧强度和放牧时间阶段密切相关外,还与该地区水热条件的变化有一定的相关性.针对长期放牧干扰的反应特性可将金露梅灌丛草场中植物划分为增加型、敏感型、忍耐型和无反应型4种类型.除了丰富度指数、多样性指数和均匀度指数外,其它一些特征参数并不支持著名的中度干扰假说.本研究发现,长期重度放牧促进了青藏高原高寒草地退化,适度放牧有利于高寒灌丛草场的生物多样性保护和牧草利用;"取半留半"的放牧原则在青藏高原草场放牧管理实践中值得推荐,它将有利于防止草场退化,提高牧草利用率和维持较高的生物多样性.%The grassland of the Qinghai-Tibet Plateau is one of the world's most remarkable grazing lands. Livestock grazing appears to exert significant effects on the vegetation and ecosystem processes on the plat-eau,although the effects of livestock grazing on grasslands are in need of further study. In this study,a long-term grazing experiment with different stocking rates in alpine Potentilla fruticosa shrubland was carried out at Haibei Alpine Meadow Ecosystem Research Station, Chinese Academy of Sciences. The effects of grazing intensity on plant species diversity,community structure,above-ground standing biomass and grassland quality were analyzed after grazing for 4,11 and 18 years which represented short-term graz-ing,medium-term grazing and long-term grazing, respectively. Our results suggest that the height and cover of plant community were decreased with the increase of stocking rate in different grazing period. The change in biodiversity and evenness indices as stocking rate increased was a typical unimodal curve after grazing for 11 years. The dominated shrub and gramnoids were replaced by the typical forbs with the in-crease of the stocking rate in the long-term heavy grazing period. Long-term heavy grazing simplifies the al-pine shrub community and decreases the standing above-ground biomass, especially palatable herbage plants. The heights and cover of plant communities were decreased as the stocking rate increased. Changes in the vegetation of different grazing treatments was also correlated with the variation in local moisture-temperature conditions except key factors such as grazing intensities and grazing time. From grazing re-lease,light grazing to heavy grazing, the dominant shrub and graminoid species were replaced by typical forbs after grazing for 18 years. All species of Potentilla fruticosa shrubland in this study can be sorted in-to 4 groups which were fostering,sensitive,tolerant and indifferent to long-term grazing disturbance. Our results did not support the intermediate disturbance hypothesis very well except three cases,i, e. , richness,biodiversity and evenness indices. It is concluded that long-term heavy grazing plays an important role in al-pine grassland degradation on Qinghai-Tibet Plateau. From responses of species diversity and standing bio-mass of different functional types to grazing,moderate grazing appears to be suitable for biodiversity con-servation and the utilization of alpine shrub grassland. The standard grazing rule of "take half leave half" is recommended as a conservative management tool to prevent grassland degradation,to improve grass utiliza-tion,and to sustain higher biodiversity on Qinghai-Tibet Plateau.
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