Study on Vegetation Community's Structure of Degraded Grassland of Noxious and Miscellaneous Grass Type

On the degraded grassland of noxious and miscellaneous grass type, according to its different degree of the degradation and the distribution of the Stellera chamaejasme L., the main noxious grass on this grassland type, the grassland can be plotted to five types: type 1, with Stellera chamaejasme density range of 0～19%; type 2, with Stellera chamaejasme density range of 20%～39%; type 3, with Stellera chamaejasme density range of 40%～59%; type 4, with Stellera chamaejasme density range of 60%～79%; type 5, with Stellera chamaejasme density range of 80%～95%. After research on the vegetation's constitution and function and the degradation regulation of the five types, the result shows that on the mountain grassland with S. Krylovii Roshev and A. cristatum L. Gaertn as the main advantage grasses, vegetation structure has relative stability. But due to herds increasing, the competition among different kind plants changed. As a result, Stellera chamaejasme L., with its special competition ability, its numbers and effects increasing step by step in the vegetation community. During the processes of the Stellera chamaejasme L increasing, the output over the ground and the density of the eatable grass such as S. Krylovii Roshev and A. cristatum L. Gaertn decreased. Following with the increasing of the Stellera chamaejasme L, the variety index Shannon-Wiener and the equality index Pielou are all changed from low to high and then to low again, but the superiority index Simpson takes on a opposite trend. At last the advanced grass of the vegetation community has been changed. Stellera chamaejasme L. changed from minor to major. So the natural grassland has been degraded by the Stellera chamaejasme L. On the basis of the above research, we have also brought forward some countermeasures to resume and enhance the production of such degraded grassland.