| The water content, soil organic matter and biological diversity are abundant in the Source Region of the Yangtze and Yellow River, which have important ecological value. In recent years, as a result of overgrazing, vegetation suffers from severe degeneration, soil erosion is more and more serious, and rare plant and animal species plummet, which have seriously damaged the balance of grassland ecosystem, and hindered harmonious development of animal husbandry. The components and functions of earth system are all related to the energy. Emergy analysis, using solar power as a unified measurement standard, has great significance for the evaluation of the environment and socio-economic development.The paper studied on the characteristics of vegetation and soil among degradation sequences of grassland in the Source Region of the Yangtze and Yellow River. Besides, it constructed emergy-based model of grazing-induced erosion on basis of the emergy analysis and analyzed vegetation-soil-livestock interaction quantitatively in order to provide scientific basis for grassland management in the Source Region of the Yangtze and Yellow River.The main results of the paper were:(1) The main characteristics of primary grassland were that the natural mortality rate of plant and the loss rate of soil organic matter caused by plant growth were high. Comparing with primary grassland, the main characteristics of lightly degraded grassland were that the natural mortality rate of plant and the loss rate of soil organic matter caused by plant growth were lower; besides, the plant growth rate and the decomposition rate of soil organic matter were higher. Compared with lightly degraded grassland, the main characteristics of heavily degraded grassland were that the plant growth rate decreased; besides, the loss rate of soil organic matter caused by plant growth and grazing-induced erosion, the natural mortality rate of animal increased. With respect to the heavily degraded grassland, the main characteristics of extremely degraded grassland were that the plant growth rate and the loss rate of soil organic matter induced by plant growth reduced; besides, the natural mortality rate of plant, the loss rate of plant caused by over-grazing, the loss rate of soil organic matter caused by grazing-induced erosion, the growth rate of animal induced by over-grazing and the natural mortality rate of animal increased.(2)Based on emergy analysis, dynamic characteristics and differences of the degradation sequences of grassland in the Source Region of the Yangtze and Yellow River was analyzed quantitatively. The results showed that grazing-induced erosion of primary grassland, lightly degraded grassland, heavily degraded grassland and extremely degraded grassland were respectively as follows: increased firstly and then reached equilibrium state, reduced firstly and then increased and decreased lastly, increased at first and then reached equilibrium state, a swing trend respectively. In equilibrium state, biomass of lightly degraded grassland was about 13 times higher than one of primary grassland, 19 times higher than one of heavily degraded grassland, 54 times higher than one of extremely degraded grassland. The animal population of moderately degraded grassland was about 8 times as many as one of heavily degraded grassland, and 10 times as many as one of extremely degraded grassland.(3) Based on emergy analysis, the measurement standard was unified. The impact factors of grazing-induced erosion of grassland in the Source Region of the Yangtze and Yellow River were analyzed comprehensively. The influence degree of all factors in descending order were: the human activities, the loss rate of plant and growth rate of animal caused by over-grazing, the loss rate of soil organic matter caused by plant growth, the plant growth rate, the decomposition rate of soil organic matter, the natural mortality rate of animal, the loss rate of plant and growth rate of animal caused by grazing based on biomass, the natural mortality rate of plants, the availability of updated resource in the environment, the loss rate of soil organic matter caused by grazing-induced erosion.(4)Artificial management could effectively adjust to the dynamic trends of grassland. For primary grassland, if the loss rate of soil organic matter caused by plant growth was reduced, as biomass increased nearly 2 times, grazing-induced erosion would be reduced by about 2 orders of magnitude. For heavily degraded grassland and extremely degraded grassland, if the loss rate of plant and growth rate of animal caused by over-grazing were reduced, as biomass increased nearly 2 times, grazing-induced erosion would be reduced more than 10 times and 3 orders of magnitude respectively. After the above human management, there were also differences between primary grassland, heavily degraded grassland and extremely degraded grassland. Primary grassland and extremely degraded grassland were similar, which emergy-based sustainability index was less than 1, environmental loading ratio was greater than 100. However, emergy-based sustainability index was greater than 10, environmental loading ratio was 0.11 in heavily degraded grassland.The main conclusions of the paper are:(1) Artificial management should be imposed to primary grassland, severely degraded grassland and heavily degraded grassland. For primary grassland, the loss rate of soil organic matter caused by plant growth should be reduced preferentially, and supplemented by reducing the natural mortality rate of plant, which can reduce the proportion of poisonous and weed plants, namely can increase the proportion of Leguminosae, Grasses and Sedges in order to reduce depletion rate of soil organic matter. For heavily degraded grassland and the extremely degraded grassland, the loss rate of plant and growth rate of animal caused by over-grazing should be reduced preferentially, and supplemented by reducing the loss rate of soil organic matter caused by plant growth and plant natural mortality rate respectively. For example, a part of the animals are sold. Besides, parts of the funds are used to purchase services. What’s more, Leguminosae can be used, which can make sure that degradation grassland restores, and can also grow well in poor environment so that soil structure and fertility are improved.(2) For artificial management of primary grassland and extremely degraded grassland, the bearing pressure of the environment will increase sharply in order to obtain higher emergy yield, which is not conducive to the harmonious development of environment and socio-economic. For artificial management of severely degraded grassland, the great effect can be achieved under less environmental pressure.(3)Utilization intensity of lightly degraded grassland is relatively reasonable, which grazing intensity is based on biomass. For artificial management of grassland in the Source region of the Yangtze and Yellow River, we can refer to utilization intensity of lightly degraded grassland. For example, we can make sure that the feed rate of plants is 0.3×biomass, at the same time, the net increase rate of number of animals is 0.01× biomass-0.01× the number of animals. |
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