| As a long-term and complex ecological project, the purposes of Converting Cropland to Forest are to rehabilitate vegetation, reduce the losses of soil & water, treat the desertification, improve the deteriorating environment, adjust the structure of rural industry, and to increase the farmers' income. With the implementation of the project completely, some theories and technology related to the project have been the focus for scientists and decision-makers. However, based on a thorough review on the current studies, we can find that the existing researches mainly concentrate on the specific technology, policies and measures, but few systematical studies on the optimum models of species distribution and the integrated assessment of ecological function.hi consideration of this issue, under the guidance of the basic principles of restoration ecology and the sustainable theory, this dissertation has systematically studied the ecological function of different species arrangement models and selects the optimum ones finally. The study is of significance on offering a theoretical foundation and scientific method for the project implementation in Western China, increasing the ecological benefits, and improving the ecological environment. Meanwhile, it is helpful for the realization of ecological sustainable development of forestry in China both theoretically and practically. The research was carried out in Datong County, Qinghai Province, where is the demonstration site for Converting Cropland to Forest. Based on analyzing industry structure, current land-use status and site classification, five models of Converting Cropland to Forest selected in low mountain and high mountain areas respectively, were investigated in field work and tested accordingly in the laboratory. The relevant analysis, factor analysis and integrated model were adopted to analyze the hydrology effects, soil quality, species diversity and productivity of different models. And the integrated ecological function was also assessed using 18 indices including water-holding capacity of soil, degree of aggregation, organic matter, hydrolytic N, rapidly available P, rapidly available K, species diversity index, and evenness of plant community. The main conclusions are as following:l)In the low-hill area, the total water-holding capacity of model C {Populus cathayana+Lycium barbarum) ranks first in different models of species distribution, up to 329.07mm. Model A (Paeonia veitchii) is better than others on the total pore space ,the final infiltration rate and structural coefficient of soil, which is 56.78%,4.8mm/min,97.61 % respectively. Model C {Populus cathayana+Lycium barbarum), having the highest average content of total N, hydrolytic N, rapidly available P, rapidly available K and organic matte , is obviously prominent in soil nutrient. As for the soil anti-scourability, model D {Hippophae rhamnoides ssp.sinensis), up to 1.136s/g, is ranked first. Model C {Populus cathayana+Lycium barbarum) has the highest biodiversity index (5.3091); model D {Hippophae rhamnoides) has the highest productivity in five models, reaching to 9.36t/(hm2.a).The results of the integrated assessment of the ecological function in low mountain area show that model C {Populus cathayana+Lycium barbarum)>mode\ A {Paeonia veitchii) >model D {Hippophae rhamnoides) > model B {Medicago etiva) > model E {Caragana korshinskii). The indexes of synthetic appraisal are 223.08, 193.20, 189.87, 155.40, and 139.89 respectively.2)In the remote-hill area, the total water-holding capacity of model F{Picea crassifolia) ranks first in different models, up to 331.91mm; Model F{Picea crassifolia) is better than others on the total pore space ,the final infiltration rate of soil, which is 53.62% and 6.8mm/min respectively. Model H {Betula latyphylla+Picea crassifolia) occupies the first place in soil structural coefficient, up to 94.751%. As to the average content of total N, hydrolytic N, total K, rapidly available K and rapidly available K, model F ranks first. The soil anti-scourability of model Y{Picea c...
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