Effects of Grazing Intensity on Dominant Population and Species Diversity and Their Typical Relationships
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.
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