Behavioural effect of grazing yak (Bos grunniens) on material circulation in east Tibetan Plateau, Qinghai Province, China

在青海省青藏高原北部和南部进行了调查。北部为典型放牧区，南部怀疑放牧区正在退化和沙漠化。本研究旨在通过对青藏高原草原生态系统中牦牛行为和物质循环的调查，为防止草原退化和荒漠化提供基础数据，最终为建立青藏高原草原牦牛可持续放牧系统奠定基础。2003 - 2006年4年间共进行了7次试验，其中在玉树州进行了3次试验，在海北州孟原州进行了4次试验。对3头牦牛进行连续3 d的行为观察和排便量记录，利用GPS跟踪放牧，采集放牧行为和放牧植物种类，放牧草地植被，粪便、植物和土壤样品，并进行化学成分分析。寒季牦牛平均反刍时间较短，粪便化学成分估算的物质循环较少，南区约为北区的一半。南部地区的牦牛甚至吃被称为“避让”的植物。从这些结果可以看出，南区可能正在进行过度放牧导致的牧场退化。即使在寒暖季轮牧，生态系统状况良好的北部立地，暖季围场也出现退化，牦牛无法摄取足够的养分进行施肥。研究结果表明，为了保持青藏高原植物多样性，防止草地退化和沙漠化，有必要研究替代放牧制度。

Investigation was carried out in northern and southern sites of in Tibetan Plateau, Qinghai Province, China. Northern one was a model grazing rangeland area and southern one was suspected that the degradation and desertification of grazing rangeland were going on. The purpose of this research was to obtain the fundamental data for preventing the rangelands from deterioration and desertification through investigating behaviour of yak and material circulation in rangeland ecosystem and for finally establishing sustainable grazing system of yak in the rangelands of Qinghai-Tibetan Plateau.Trial was carried out totally seven times, 3 times in Yushu Prefecture, Yushu State and 4 times in Mengyuan Prefecture, Haibei State during 4 years from 2003 to 2006. Consecutive three day recording of behavioural observation and amount of feces excreted for 3 yak cows, grazing tracking with GPS apparatus, grazing behaviour and plant species grazed, vegetation of grazing rangelands, and samples of feces, plants and soils were collected and the chemical compositions were analyzed.Average rumination time of yak in cold season was shorter, material circulation estimated by chemical composition of feces was smaller and approximately a half in southern site than in northern one. Yaks in southern site grazed even the plant species known as avoided. From these results, it is suggested that deterioration of rangeland by overgrazing might have been in progress in southern site.Even in northern site where rangeland was rotationally grazed in warm and cold seasons and was recognized the ecosystem being in good condition, it was indicated that warm season paddock was degraded and yak could not intake nutrition enough for fertilization.From these results, it is considered that alternative grazing systems should be investigated for maintaining floral diversity and preventing grazing rangeland from deterioration and desertification in Qinghai-Tibetan Plateau.