Abstract: Fencing is an economic and effective tool to improve the grassland conditions.The effects of different fencing term(1,4,7,11,and 17 years) on the vegetative composition and structure of desertification grassland were studied in Hulunbeir,Inner Mongolia Autonomous Region.Natural restoration started from the invasion of annuals,such as Artemisia halodendron Turcz.ex Bess.etc.and their important values in the enclosed section of 7,11,and 17 years,were 1.57,1.78,and 1.37 times of that in the enclosed section of 4 years,respectively.Annuals tended to decrease and Agriophylluns arenarium Bieb.disappeared completely in the enclosed section of 11 years.Vegetation coverage showed an average increase of 4.6 times and the average grass-layer height increased 75.3%.The community similarity coefficients were the largest at 0.9630 and 0.7143 for 17-year vs.11-year enclosure and 1-year vs.4-year enclosure,respectively.The results show that the vegetative community changed along with fencing years from annual species to shrub species and perennial grasses step by step,and the species richness,diversity,and evenness also increased.However,it was a very long procedure of species competition and ecosystem renovation during natural restoration of desertification grassland.The results indicate that vegetative ecosystem of Hulunbeir desertification grassland was still fragile and would be prone to desertification again under the disturbance due to a high proportion of annual species even after 17-year enclosure.

Key words: Desertification grassland, Enclosing effect, Bio-diversity, Hulunbeir steppe

摘要： 2004年,在内蒙古呼伦贝尔沙化草地,测定围封不同年限(1、4、7、11、17年)沙化草地群落的特征值,分析围栏封育对沙化草地植被特征及生物多样性变化的影响。植被的自然恢复从一年生植物的侵入开始,差巴嘎蒿(Artemisia halodendron Turcz.ex Bess.)等重要值在围封第7、11和17年分别为第4年的1.57、1.78和1.37;一年生植物呈减少趋势,沙米(Agriophylluns arenarium Bieb.)在围封第11年完全消失。植被盖度平均增长4.6倍,草层高度平均增高75.3%。围封17和11年、1和4年,群落相似系数最大,分别为0.9630和0.7143。结果表明:沙化草地围封后,由于干扰源解除,群落组成发生了规律性变化,植物群落逐渐由不稳定的一年生植被向次稳定的灌丛化植被和相对稳定的干草原植被过渡,随着围封年限的增加,群落结构逐渐趋于合理,物种丰富度、多样性和群落均匀性不断增大,但沙化草地围封后的植被近自然恢复也是一个漫长的系统修复与竞争过程。呼伦贝尔沙化草地经过17年的围封,植被系统仍十分脆弱,群落中一年生植物仍占有较大比例,受干扰后极易发生再度沙化。

关键词: 沙化草地, 围封效应, 植物多样性, 呼伦贝尔