摘要:由于全球气候变化及过度放牧等不合理利用，灌木入侵草地已经成为干旱半干旱草原区的一种普遍现象。本研究在内蒙古锡林郭勒草原区选择3处不同围封恢复年限（围封时间分别为1979，1983和2003年）的小叶锦鸡儿（Caragana microphylla）灌丛化草地，分析了围封年限对灌丛化草地关键种小叶锦鸡儿种群大小格局及灌丛间主要物种种间关联的影响，并从群落内物种生态位配置情况方面进行了相关机制的探讨。结果显示：（1）小叶锦鸡儿的冠幅大小分布结构的偏态系数在8/9的样区内大于0，表现为正偏态；随着围封年限的延长，在低、中灌丛化样区内，小叶锦鸡儿的冠幅有增大的趋势，这主要是由小于0.5 m冠幅的小叶锦鸡儿的减少或者消失导致的；（2）随着围封年限的延长，灌丛间多年生禾草生态位宽度（B）逐渐增大，表现为B_1979围封 > B_1983围封 > B_2003围封；灌丛间主要物种种间关系由负关联作用（竞争作用）向正关联作用（促进作用）转变。本研究结果不仅揭示了围封条件下小叶锦鸡儿灌丛化草地群落结构的变化及发展趋势，同时也从关键种小叶锦鸡儿种群大小格局及灌丛间主要物种种间关联的角度对相关机制进行了解释，为该区域的合理利用及恢复政策的制定提供了数据支持及理论指导。



Abstract:Due to global climate change and anthropogenic disturbance such as overgrazing, many arid and semiarid grasslands have been encroached by shrubs during recent decades. In this study, three Caragana microphylla shrub-encroached grasslands with different exclusion restoration periods (fenced since 1979, 1983 and 2003, respectively) were selected in Xilingol steppe region to analyze the effects of enclosure period on the population size structure of C. microphylla and the interspecific associations among main species in the shrub interspaces. In addition, we tried to analyze the corresponding mechanisms by testing niche space distribution of species in the shrub interspaces. (1) The skewness of size structures of C. microphylla was positive in eight out of nine plots, indicating significantly positive skewness. The size of C. microphylla increased with the elongation of enclosure period in the low or middle shrub coverage plots, mainly due to the decrease or disappearance of C. microphylla less than 0.5 m. (2) With the elongation of enclosure period, the niche width (B) of perennial grasses in the shrub interspaces increased, i.e., B_{1979 Fenced} > B_{1983 Fenced} > B_{2003 Fenced}, and the interspecific associations among main species in the shrub interspaces shifted from negative association (competition) to positive association (facilitation). The findings not only revealed the community dynamics and tendency of C. microphylla shrub-encroached grasslands under fencing condition, but also provided insight into the corresponding mechanisms in terms of C. microphylla's population size structure and the interspecific associations among main species in the shrub interspaces. The results would provide experimental data and theoretical guidance for the rational utilization and restoration policy-making in the shrub-encroached grasslands.





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