Effects Of Different Grazing Rates On Population Characteristics Of Stipa Grandis In Typical Steppe

Stipa steppe is one of the most representative types of grassland in typical grasslands.It is also the main grazing pasture and mowing field in the typical grassland of China.As an excellent pasture in typical grassland,Stipa grandis has the characteristics of high nutritional value,easy digestion and eating by livestock.In this paper,we study the different characteristics of S.grandis under different grazing rates.Based on the point pattern analysis theory,using the pair correlation function and selecting the complete spatial randomness to analysis of the changes and adaptation characteristics of S.grandis population in typical grasslands to different grazing rates.The results showed that:1.The number and leaf traits of the S.grandis showed increase first and then decrease with the rate of grazing.Under light grazing conditions,the value of average height,average coverage,dry weight above ground and important value are the highest in all grazing rate,but the lowest in heavy grazing.The value of natural leaf width,total leaf width,leaf length,leaf height,leaf dry weight,leaf rolling index and leaf length/ leaf width are the highest in mild grazing levels,but the lowest in severe grazing.2.The growth and reproduction ability of the individuals of S.grandis is strengthened in the light grazing rate,and population characteristics are better than non-grazing treatments.However,there are significant differences from non-grazing treatment that individual growth and birth is restricted under severe grazing rate.Population size of S.grandis with different bunch sizes show increase first and then decrease in different grazing rate,at the G level and H level the value reached the highest(5.1cm< r< 9.0cm).Bunch hollowing reaches about 50% on all gradients at F level(4.1<r<5.0 cm)and have differences between the gradients.According to the Godorn Index,the most stable condition of the S.grandis population appears in the light grazing treatment.3.The total area of hole of S.grandis population is significantly higher than that of non-grazing treatment under grazing conditions(P< 0.05),but the population territory area,population distribution density and territory density decreased significantly(P< 0.05).S.grandis populations show aggregated distribution at small scales under different grazing rates.As the spatial scale increases,populations tend to be randomly distributed or regular distributed.Under the condition of non-grazing and medium grazing,the distribution pattern of spatial pattern of S.grandis population converged,and the aggregate distribution on the small scale showed an increasing trend.Under the condition that the grazing rate continues to increase,the spatial scale of random distribution gradually expands.Overall,compared with the control treatment,the adaptability of the S.grandis population to grazing shows that,under the light grazing rate,the aggregation scale of the spatial pattern of S.grandis decreased,and the random distribution pattern dominated.We should take a contraction strategy in space to increased height,tillers density and biomass for individual internal regulation of strains.Under moderate grazing rates,the population still shows aggregation in the spatial pattern,with no significant changes in population characteristics,and the important values remain unchanged.Under the heavy grazing rate,the population of S.grandis changed from aggregated distribution to random distribution.Population characteristics height,tillers densities and biomass were reduced,the quantity of bunch failed to regulate,resulting in plaque fragmentation,and important values decreased significantly.