内蒙古典型草原物种组成和群落结构对长期放牧的响应

RESPONSE OF PLANT SPECIES COMPOSITION AND COMMUNITY STRUCTURE TO LONGTERM GRAZING IN TYPICAL STEPPE OF INNER MONGOLIA

该文比较研究了内蒙古羊草草原和大针茅草原放牧演替系列经过20a(1985～2005年)放牧,利用群落组成与结构的变化分析了这两个放牧演替系列上15个植物群落的变化趋势,并依此探讨长期放牧对草原生态系统结构和功能的影响。结果表明:在大针茅(Stipa grandis)牧压梯度系列上,群落仍以大针茅群系为主,冷蒿(Artemisia frigida)为建群种的群落消失;在羊草(Leymus chinensis)牧压梯度系列上,羊草和冷蒿不再是建群种,被西伯利亚羽茅(Achnatherum sibiricum)、大针茅、冰草(Agropyron cristatum)和糙隐子草(Cleistogenes squarrosa)所替代。综合两个牧压梯度系列的研究结果得出以下基本结论:长期过度放牧进一步加速了草原群落的退化进程,但退化草原具有较高的恢复弹性,控制放牧使部分群落得到一定程度的恢复。同一植物群落时间变化,或不同演替阶段的植物群落在空间序列上的位移程度主要取决于放牧史和利用强度。过去20a中,特别是2003年以来草原管理政策的改变并没有导致该区域草地的整体退化,而是在一定程度上有利于草地的恢复。

Aims We studied （a） spatial patterns in typical Leymus chinensis and Stipa grandis steppe communities along two grazing gradients and （b） changes in plant species composition and community structure over a 20-year period in Inner Mongolia, with the objective of understanding grazing-associated grassland dynamics. Methods Grassland communities were investigated in 1985 and 2005 on 15 field sites, seven along a grazing gradient in S. grandis steppe and eight along a grazing gradient in L. chinensis steppe. Changes in spatial and temporal patterns of these steppe ecosystems were examined and analyzed in association with changes in land use intensity in the region. Important findings For the S. grandis steppe, five of the seven sites showed a trend towards increas-ing dominance of S. grandis after 20 years, whereas the other two sites showed signs of degradation. For the L. chinensis steppe, six sites exhibited a trend towards restoration of community composition and structure and two sites displayed the reverse trend. Changes in spatial and temporal patterns in both S. grandis and L. chinensis successional communities were mainly due to a shift in grassland management regimes in 1985–2005. Long-term heavy grazing accelerated grassland degradation, and decreased grazing intensity promoted grassland restoration processes. During the past 20 years, especially after 2003, the change in grassland management policy has not resulted in overall grassland degradation in the region; rather it has brought about a more spatially balanced grassland use.