Study On The Effect Of Conversion Of Cropland To Forest And Grassland In Hilly And Gully Region Of The Loess Plateau Based On Emergy Analysis

The effect of conversion of cropland to forest and grassland has been a focus issue in the academic field. It is difficult to assess the effect for two reasons. One reason is that different kinds of input and output which are from a mass of material flow, currency flow and energy flow in the conversion project are hard to compare. The other reason is that the input means of production and output product often have large price fluctuations, as the project spans a long period of several years. By emergy analysis we can convert different kinds of input and output to solar emjoules for comparison. Thus, emergy analysis was introduced to study on the effect of conversion of cropland to forest and grassland in hilly and gully region of the Loess Plateau. On one hand, it made possible to compare different kinds of input and output in the project. One the other hand, it eliminated the disturbance of price fluctuations. In short, emergy analysis made the study results more objective.At the beginning of dissertation, the study background was analyzed, and according to the project status of conversion of cropland to forest and grassland in China the study objective and significance were expounded. On this basis domestic and foreign study findings about emergy and conversion of cropland to forest and grassland were reviewed, which showed that the combination finding of the two field was rare. Then, Pengyang County in Ningxia was selected as study area, and the general situation of Pengyang County was described from five aspects. Besides, relevant issues of the study were discussed.In the main body of dissertation, emergy analyses of cropland ecosystem, forest ecosystem and grassland ecosystem in Pengyang’s project were performed, which included emergy diagrams, emergy analysis tables, emergy input and output, and emergy indices in the period from2000to2010. On the basis of the results, three emergy indices of combined system were analyzed in order to assess the effect of project. Moreover, as a supplementary assessment, the value of cropland, forest and grassland ecosystem services of Pengyang County from2000to2010was analyzed based on remotely-sensed data.Finally, according to the results of emergy analysis and ecosystem services value analysis, conclusions were showed as follows.(1)The results of both emergy analysis and ecosystem services value analysis showed that overall the project for conversion of cropland to forest and grassland in Pengyang County achieved benefit. On the other hand, the result of ecosystem services value analysis indicated that the project did not change the ecosystem-setup of Pengyang County in essentially.(2) In emergy analysis, the emergy output and input ratio of cropland-forest-grassland combined system showed that benefit of the project was low in terms of numerical value. Moreover, the environmental load ratios of forest ecosystem and grassland ecosystem exhibited that environmental stress generated by forest construction and grassland construction was far below the local carrying capacity. In the future, forest and grassland construction should be strengthened and the emergy structure should be further optimized for more benefit of project.(3)The result of ecosystem services value analysis showed that the input for forest construction was much more than for grassland construction in the implementation process of project, which illustrated an excessive imbalance between the two. Besides, in emergy analysis, the stability index of forest-grassland combined system demonstrated that the material flow net and energy flow net in forest-grassland combined system constructed in the project were underdeveloped, which resulted in poor self-adjusting and vulnerability.To some extent, all of the above restricted the project’s benefit.(4) In emergy analysis, the emergy output and input ratio and emergy yield ratio of cropland ecosystem showed that the subsidy and assistance grain were obviously low, which would severely affect the enthusiasm for participating in project and the further implement of project. In the future subsidy and assistance grain should be increased.(5) The results of main emergy indices analysis of forest ecosystem showed that many problems existed in the forest construction of project, which would have a negative impact on the benefit of project.(6) The results of main emergy indices analysis of forest ecosystem showed that the grassland construction in project had poor quality.