Abstract:

The study on the changes in the relationship between the importance value of dominant populations and species diversity caused by different grazing intensities can provide theoretical support to the protection of grazing grassland and the restoration of degraded vegetation. This study choosed the Stipa breviflora desert steppe in Inner Mongolia as the research object, adopting a single factor randomized block design (CK, control; MG, moderate grazing; HG, heavy grazing). The survey was conducted on the height, coverage, and density of plant communities in each plot, then calculating the important value of dominant population and species diversity, exploring the relationship between them by comparative analysis and canonical correlation analysis. The results are as follows: With the increase of grazing intensity, the importance value of S. breviflora increased while the species richness index decreased. The dominance index was highest and the diversity index was lowest under the MG treatment. A canonical correlation analysis between the important value of dominant population and the species diversity showed that the cumulative contribution rate was largest in the MG treatment (96.060%) while it’s smallest in the CK treatment (90.160%). The increasing of grazing intensity reduced the complexity and dimension of the relationship between the importance value of dominant populations and species diversity (from 2 canonical correlations to 1 canonical correlation). In CK treatment, the increasing of the importance value of each dominant population would decreased the plant community diversity index, and the increasing of the importance value of Cleistogenes songorica and Allium polyrhizum would increased the plant community evenness index. In MG treatment, the increasing of importance value of S. breviflora would decreased the dominance index. In HG treatment, the increasing in the importance value of S. breviflora and C. songorica reduced the diversity index. For the important value of dominant population and the species diversity index, the correlation with its own typical variables was more complicated, while the correlation with the corresponding typical variables was relatively simple. The number of significant correlation coefficients in CK, MG and HG treatments was 15, 20 and 12, respectively. Therefore, the relationship between the importance value of dominant populations and species diversity was the most complex in MG treatment. In conclusion, the plant community have the most complex in the MG treatment, however, in the HG treatment, the plant community are more susceptible to external environmental interference, and it is relatively difficult to restore the original state after the degradation of grassland plant communities.

Key words: desert steppe, grazing intensity, dominant populations, species diversity, canonical correlation, comparative analysis

摘要：

研究不同放牧强度所引起的优势种群重要值和物种多样性相互关系之间的变化过程，可为放牧草地保护和退化植被恢复提供理论依据。以内蒙古短花针茅（Stipa breviflora）荒漠草原为研究对象，采用单因素随机区组试验设计（CK，对照区；MG，中度放牧区；HG，重度放牧区）对植物群落的高度、盖度和密度进行调查，计算优势种群重要值和物种多样性后，结合对比分析和典型相关分析研究方法来探究二者之间的关系，结果表明，伴随放牧强度增加，短花针茅的重要值增大，丰富度指数下降。MG处理区下的优势度指数最高，多样性指数最低。对优势种群重要值和物种多样性进行典型相关分析表明，其累计贡献率在MG处理区最大（96.1%），CK处理区最小（90.2%）。放牧强度增加会降低优势种群的重要值与物种多样性相互关系的复杂性和维度（由2个典型相关变为1个典型相关）。在CK区，各优势种群重要值增加均会导致植物群落多样性指数下降，无芒隐子草（Cleistogenes songorica）和碱韭（Allium polyrhizum）重要值增加会导致植物群落均匀度指数增大。在MG区，短花针茅重要值增加会导致植物群落优势度指数下降。在HG区，短花针茅和无芒隐子草的重要值增加会降低多样性指数。各优势种群重要值和各物种多样性指数与自身典型变量的相关性之间较为复杂，与对应典型变量的相关性之间较为简单。CK、MG和HG处理区存在显著相关系数的个数分别为15、20和12个，MG处理区下优势种群重要值和物种多样性的相互关系最复杂。综上，中度放牧处理区下的植物群落不易受外界环境的干扰，重牧处理区下的植物群落更容易受外界环境干扰，草地植物群落退化后相对困难恢复到原有状态。

关键词: 荒漠草原, 放牧强度, 优势种群, 物种多样性, 典型相关, 对比分析