The Tibetan steppe with its strong continental climate is one of the most severe environments in the world.Tibetan pastoral grazing system is a special system with mixed different animal species,including yak,sheep,goat and horse etc.Each species has its own specific characteristics and adaptations to the environment.Despite the harsh environments,rangelands on the Tibetan steppe provide forage for an estimated 12 million yak and 30 million sheep and goats that support the livelihoods of about 5 million pastoralists (Dennis et al.,2006).Yak and sheep are the two main species in the grazing system.The mortality of sheep is higher than yak during harsh winters and springs,but with higher restocking rate than yak.Although yaks characterize Tibetan pastoralism,sheep are usually more important economically.Sheep are more common than yaks in the western regions of Qinghai‐Tibetan plateau because sheep can browse shorter grass than yak and sheep can be sold out much sooner than yak.An average nomad family may raise 300 to 400 sheep in this area.Sheep provide wool and meat and milk.Sheep meat is the preferred meat among nomads as well as in agricultural and urban areas.The wool from Tibetan sheep is also one of the best carpet wools in the world.Because overpopulation and overuse of natural resources are causing fundamental social and economic changes among the herding households,the livestock flock structure is also changing accordingly towards a market economy,e.g.the proportion of Tibetan sheep with good wool and meat quality increase.
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