关键词: 围封年限, 大针茅, 群落特征, 种群特征

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