Abstract: Stipa grandis steppe is the common stable,representative form of typical steppes in the Inner Mongolia plateau.It is not only an important pasture for Inner Mongolia,but also an important green protective windbreak for Beijing-Tianjin area,and has considerable ecological and economic importance.Recently,the area of degraded S.grandis steppe has rapidly expanded due to increased human disturbance and animal overgrazing.The restoration of degraded grassland is of prime importance in restoration ecology.Most studies have focused on the variation of the vegetation and soil characteristics after restoration with little research attention on the restoration of constructive species.In fact,it was considered that restoring vegetation of constructive species could be sustained by its own growth,which was the key influence on the success of the restoration.In the present study,we used the S.grandis populations in the continuous grazing pasture as a control,and selected fencing S.grandis populations at different times as research objects that had been fenced for 4 years,9 years and 29 years,respectively.We investigated the fencing times affecting the variations of the S.grandis population and communities in the restoration process using a quadrat survey method.Results showed that fencing had an impact on the communities and the populations of S.grandis during grazing.The diversity and the number of species of community increased with fencing time compared to that in the grazing plot.After being fenced for 9 years,the structure and component of the fenced community was similar to that of the original community.The number of perennial forbs and shrubs and semi-shrubs increased in the site fenced for 29 years.The population and morphological characters of S.grandis increased with fencing time and then decreased after being fenced for 9 years.Features of S.grandis in plot fenced for 29 years were significantly lower than those in plots fenced for 9 years.The reproductive allocation of S.grandis also increased with fencing time then decreased after fenced for 9 years.The specific leaf area decreased with fencing time,but the mass-based leaf nitrogen concentration decreased with fencing time and then increased after being fenced for 9 years.Results suggested that long term fencing had a negative impact on the growth and development of plant species and community when the pasture was in recovery after being fenced for 9 years.

Key words: Fencing time, Stipa grandis, Community character, population character

摘要： 为研究围封时间对退化草地恢复过程中的建群种种群特征以及群落特征的影响,于2008年7月以自由放牧的草地群落和大针茅(Stipa grandis P.Smirn)种群为对照,选取围封不同年限(围封4年、围封9年和围封29年)的草地群落进行样方调查,分析围封不同年限后植物群落和大针茅种群特征的变化,以期为退化草地建群种的恢复提供理论基础。结果表明:不同围封年限对植物群落和大针茅种群特征存在显著影响;随着围封年限的延长群落多样性和物种数目逐渐增加,围封到9年后,群落优势种和结构组成与原生境的相似,在围封29的样地中多年生杂类草和小灌木或半灌木种类增加;建群种大针茅种群特征和个体形态性状如生殖枝高度、营养枝长度和营养枝叶鞘长度等随着围封年限的延长呈增加趋势,围封9年后呈降低趋势,大针茅繁殖分配的变化趋势与形态特征变化趋势相似;大针茅比叶面积随着围封年限的延长呈逐渐降低的趋势,而叶片氮含量呈先降低后增加的趋势。这表明长期完全围封会对大针茅种群的更新存在负面影响。

关键词: 围封年限, 大针茅, 群落特征, 种群特征