Health Assessment Of Alpine Grassland Ecosystem In Northwest Sichuan

The evaluation of grassland ecological system health is the hot spot in the field of international academia, research in this field reflects the level of recognition that people to grassland ecological system, but the study is still at primarily stage in our country. The northwestern Sichuan alpine grassland is located on the southeastern fringe of the Qinghai-Tibetan Plateau (QTP), its grass possesses excellent quality and rich in plant species. Nevertheless, the northwestern Sichuan alpine grassland have been obviously degenerated and the quality of grass have become deterioration because of the lack of scientific management and the excessive exploitation of the grassland resources. Thus, understand and grasp the health of the northwestern Sichuan alpine grassland, which contributes manager to know grassland condition, accordingly, and make the rational use of grassland is possible.The study area is located in Anqu township, Hongyuan county, Aba Prefecture, Sichuan province. In order to more close to the production practicality, we selected three joint ranching households whose environmental parameters were kept constant, according to actual research the livestock capacity and grassland area, we confirm the livestock capacity of winter pasture and summer pasture were 0.61,0.97,1.21 Yak/ hm2 and 1.14,1.33,1.90 Yak/hm2, respectively. We confirmed the suitable livestock capacity of Anqu township, which by comparing the change of vegetation and soil characteristics between the winter pasture and summer pasture under three different grazing intensity. Meanwhile, We evaluated the health state of grassland ecological system of the Anqu township, Hongyuan county of northwestern Sichuan in 2012.The experiment results are as follows:1. As the livestock capacity increased, the dominant species of winter slope pasture-such as Carex enervis, Elymus nutan and Kobresia setchwanensis gradually reduced, while forbs-such as Potentilla anserina and Potentilla discolor gradually increased; The dominant summer ground pasture species, Carex muliensis, transformed to Blysmus sinocompressus, Deschampsia caespitosa, Carex meyeriana and Kobreria tibetica. In the winter pastures and summer pastures, the maximum value of aboveground biomass appeared under moderate grazing (274.90 g/m2) and light grazing (351.45 g/m), respectively; Both the rate of good herbages of the winter pastures (80.08%) and summer pastures (98.41%) all reached highest under light grazing, what’s more, as the grazing intensity increased, the proportion of good herbages decreased. The diversity index reached maximum under moderate grazing, heavy grazing (2W,3W) and moderate grazing (2S), respectively; While the soil nutrient have no significant difference in the winter pasture and summer pasture with different grazing intensities (P> 0.05). In the present study, by the comprehensive analysis of the vegetation characteristics and the soil nutrient features, we found that the suitable livestock capacity of winter pasture is 0.97 Yak/hm2, and summer pasture is 1.33 Yak/hm2 in the Anqu township, Hongyuan county of the North-Western Sichuan.2. We used factor analysis method to explain the survey data and so determine the objective weights of indexes. In the vegetation status, the weights of indexes of the dominant species height (0.068) and the good herbages (0.067) reached the highest, in the soil status, the weights of index of the soil organic matter (0.123) was highest, the weights of index of the grazing intensity was 0.055 in the grazing disturbance.3. According to the results of the health state evaluation, it shows that the evaluate results of winter pasture that are similar to summer pasture, their overall index are 4.203,3.808 and 4.214,4.021, respectively. The two changes trend are same, as the grazing intensity increased, the health of the grassland system is getting worse.4. We through three different aspects, such as the vegetation condition, soil, condition and disturbance condition, the essay employed 16 indicators in order to build the index system, such as, the aboveground biomass, proportion of good grass, the poisonous plants, constructive species, invading species, litter, the height of dominate species, vegetation coverage, plants species richness, soil organic matter, the soil total N, P and K, soil bulk density, proportion of bare land and grazing intensity. We used the winter pasture and summer pasture with the suitable livestock capacity as reference area. Further more, we used general index method to establish evaluation index system。The overall index of grassland ecosystem health in Anqu township, Hongyuan county is 4.031, the threshold of overall index of health between H2 (health) and H3 (sub-health) is 4.0, so while that Anqu township grassland ecosystems in the health condition and have been biased in favor of sub-health level, which should arouse the high concern of the manager and society.