Overgrazing by domestic livestock has greatly degraded many arid and semiarid grassland ecosystems around the world.However, potential for the recovery of ecosystems following removal of grazing stock is poorly known. To evaluate possibility of recovery under natural conditions by protection from grazing in the degraded semiarid Mu Us Sandland in northem China, we examined three grazing treatments: continuous year-long livestock grazing (grazing), grazing excluded for 5 years (5-yr exclosure)and grazing excluded for 16 years (16-yr exclosure), analysed the effects of grazing exclusion on coverage of plants, plant species richness, similarity and diversity. Species richness was significantly higher under ungrazing treatment than under grazing, and the changes in richness caused by grazing exclusion varied with spatial scales (from 1 to 1000 m2). Subshrub coverage increased under the 5-yr exclosure treatment but decreased under the 16-yr exclosure. Herb coverage increased consistently with grazing exclusion.The 16-yr exclosure treatment induced a shift of the dominant species from an encroaching subshrub Artemisia ordosica to a key steppe grass Stipa bungeana, which signaled the beginning of recovery for sandy grassland from subshrub- to grass-dominated. The results suggest that it is possible to restore the sandy grassland vegetation in this region by protection from grazing if it has long enough time.%围栏禁牧是一种使退化草地获得自然恢复的低投入措施.通过对毛乌素沙地3种放牧管理类型(持续放牧、围栏禁牧5 a和围栏禁牧16 a)的物种组成、盖度、丰富度、多样性、相似性进行比较研究,目的是阐明退化毛乌素沙地植被在禁牧条件下自然恢复的可能性和其恢复演替的趋势.研究发现,围栏禁牧5 a左右群落物种组成就会有较大的恢复,但是物种多度增加程度却不大,即去除放牧干扰后群落物种丰富度的恢复要比物种多度的恢复更容易;禁牧后恢复的种类主要是一些不耐牧但适口性好的物种;围栏禁牧16a后草本盖度大大增加而半灌木盖度却减少了,且出现了半干旱草原的重要典型种--本氏针茅StipabungeanaTrin.,这标志着以油蒿ArtemisiaordosicaKrasch.为主的退化灌丛沙地开始向以禾本科草为主的半干旱沙质草原方向恢复;但要实现毛乌素沙地更大尺度上物种丰富度的恢复,围栏恢复的时间还需要更长.
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