退化草原冷蒿群落13年不同放牧强度后的植物多样性

放牧过程通过家畜的啃食、践踏干扰草原环境，使草原的物种组成发生变化，植物种群的优势地位发生更替。对退化草原中的冷蒿群落在经历13a不同放牧强度——无牧（0．00只羊，hm^2）、轻牧（1．33只羊／hm^2）、中牧（4．00只羊／hm^2）、重牧（6．67只羊，hm^2）的围栏放牧后的植物群落多样性进行研究，结果表明：经过13a的演替变化，（1）无牧处理下植被密度显著低于其它3个放牧处理下的植被密度，而其它3个放牧处理之间的植被密度差异不显著；（2）无牧处理下羊草成为群落的优势种，轻牧和中牧处理下冷蒿依然是群落的优势种。这3种处理下寸草苔的种群密度最大；重牧处理下优势种变为星毛委陵菜，并且其种群密度最大；随着放牧强度增加，不同放牧退化阶段指示植物的种群密度的变化趋势是：冷蒿为先增大后减小，而星毛委陵菜为先急剧增大，然后平缓增大，最后再急剧增大；（3）植物多样性和均匀度指数在中牧处理下最大，在无牧处理下最小，说明中牧处理下群落的多样性最高，无牧处理下群落的多样性最小。而优势度指数正相反。植物群落结构和多样性的变化主要是由放牧家畜选择性采食、不同植物对放牧响应的不同策略、植物种间的竞争、动植物协同进化以及由放牧改变的土壤理化性质等因素综合决定的。此研究有助于进一步认识退化草原在继续放牧干扰下的演替规律以及为退化草原的保护和恢复提供理论依据。

Plant biodiversity of Aretemisia frigida communities on degraded grasslands under different grazing intensities after thirteen-year enclosure

Artemisia frigida communities on Chinese Inner Mongolia steppe have been grazed by sheep in enclosures for thirteen years under four grazing intensities: zero-grazing (0.00 sheep/hm2), light-grazing (1.33 sheep/hm2), medium-grazing (4.00 sheep/hm2), and heavy grazing (6.67 sheep/hm2). The plant biodiversity was investigated from July to August in 2002. The results showed that: (1) Under zero grazing, the vegetation density was significantly less than that under light, medium or heavy grazing. The difference of the vegetation density was not significant among the latter three grazing treatments. (2) After thirteen years, the dominant plant became Aneurolepidium chinense under zero grazing, but still was A. frigida under light and medium grazing. However, the population density of Carex duriuscula was largest under above three grazing treatments. Under heavy grazing, Potentilla acaulis became dominant and its population density was largest in the community. With grazing intensities increasing, the population density of indicators of the grassland degradation in different degraded phases first increased, and then decreased for A. frigida, while first sharply increased, then gradually increased, finally sharply increased again for P. acaulis. (3) Diversity and evenness indices were largest under medium grazing, but smallest under zero grazing, which showed that the plant diversity was highest under medium grazing, but lowest under zero grazing. Dominant indices were contrary to the above two indices. Community structure and plant diversity were controlled by the integrated influence of selective browsing of sheep, adaptive strategies of different plants to grazing, interspecific competition, co-evolution between animal and plant and physical and chemical characteristics of the soil changed by grazing. These findings were contributed to provide an insight into the successive theory of the degraded grassland under the continuous disturbance of grazing and provide a theoretical foundation for the protection and restoration of the degraded grassland.