Evaluation On The Ecological And Economic Benefits Of The Conversion Of Cropland To Forest (Grassland) In Weibei Rainfed Highland

Global environmental problem caused by soil erosion and land desertification has become one of the problems that threaten to human survival and development.Returning farmland to forest (grassland),the resumption of grass vegetation is one of the fundamental measures to control soil erosion and desertification,Since 2001,China has practice the policy of converting cropland into forest and grassland,up to today,it hasn't been carried out for a long time.Since 1972,the Hanjia tableland of Xiaoqiu town of Yaozhou district has been gradually carried out returning farmland to forest(grassland),and achieved a very significant ecological and economic benefit.This paper sets runoff field in different vegetation coverage conditions and visits farmers and other forms,collect some basic data for agro-ecological economic system of the Hanjia tableland of Xiaoqiu town of Yaozhou district,combines with the theoretical method of energy analysis,analysis the change of ecological and economic benefits of the area since the policy of returning farmland to forest (grassland) has been practiced,in order to evaluate the benefit by returning farmland to forest (grassland) on a longer time scale,which has important directive significance to practice rationality the Loess Plateau Watershed ecological construction.And it also can supply some scientific evaluate evidence for some regions like the Loess Plateau to research and evaluate the effect of returning farmland to forest engineering and provide theoretical basis for Benefit Evaluation of the soil and water conservation and ecological construction.The results show that:(1) 35 year locust stands after returning farmland basically formed without suspension materials,but cut slash and bare land formed with a large number of suspended load.the average surface runoff of locust stands,cut slash and bare land was 52.51 m³,63.65m³,100.96m³ respectively; the runoff of locust stands and cut slash are respectively 52.01 percent and 63.04 percent of bare land; sediment productions are respectively 0.13 kg/m³,0.28 kg/m³,1.10kg/m³;the sediment productions of locust stands and cut slash are respectively 11.81 percent and 25.45 percent of bare land.Runoff coefficient are respectively 0.74,0.81,1.10.Runoff coefficient of locust stands and cut slash are respectively 11.81 percent and 25.45 percent of bare land;it tells us that a part of locust stands rain can be absorbed and converted to underground runoff.It showed that the Capability of Soil and Water Conservation of locust stands is better than cut slash and bare land.Because locust stands have developed root system,runoff coefficient and less sediment productions,Soil and Water Conservation has better Capability.As cut slash is covered by fasciculation plants,Soil Erosion is less than bare land and runoff was 63.04 percent of bare land and sediment productions is 25.45 percent of bare land,the runoff coefficient is 62.82 percent of bare land.According to it,we can find that vegetation has the important role in soil and water conservation.From the intensity of erosion, bare land is the dramatic,cut slash is the moderate and locust stand is very slight,almost no erosion.(2) Before returning farmland to forest(grassland) locust stands and cut slash ecosystems of vegetation for soil conservation value is 106.32×10⁴ yuan in 1972,cutting of vegetation and soil conservation track value is 89.42×10⁴yuan.And locust woodland ecosystems of vegetation for soil conservation value is 108.93×10⁴yuan in 2006 Hanjia plateau,cutting of vegetation and soil conservation track value is 94.17×10⁴yuan,the entire study area in 2006 the soil of vegetation to maintain value of the total value is 277.33×10⁴ yuan,the total soil value of farmland increased by 7.6 percent before returning farmland to forest(grassland),which proved that the measure protect the ecological environment took a veryimportant role.(3) Economic benefit is notable after returning farmland to forest(grassland),the input of the energy of agricultural eco-economic systems decreased but output increased.The total input of the energy was 2.99×10¹⁷sej,it decreased 2.60 percent than before returning farmland to forest (grassland).Among them the renewable energy of environment and resources,nonrenewable energy of environment and resources and industrial auxiliary energy were27.85 percent,6.58 percent and 30.56 percent.The nonrenewable industrial auxiliary energy was 9.14×10¹⁶ sej which mainly comes from agricultural chemical fertilizer and power and accounts for 91.57 percent of the total auxiliary energy,the energy value of chemical fertilizer takes up high rate in industrial auxiliary energy,which reached 90.15 percent.After returning farmland to forest(grassland) Hanjia Plateau total output value was 6.46×10¹⁷sej.From the composition of energy output,the planting is 3.25 percent,the fruit industry is 94.27 percent,animal husbandry is 2.16 percent,the subsidies is 0.45 percent,so output value of agriculture and forestry are the main parts.Woodland energy increased from 1.24×10¹⁷ sej in 1972 to 6.09×10¹⁷ sej in 2006,the rate of increase is up to 391 percent,and the average annual growth rate reaches 9.77 percent.(4) The dominance index of agroecosystem decreased form 0.423 to 0.402 after returning farmland to forest(grassland) in Hanjia tableland,it mainly presented the energy output of agricultural products system was low.Although the energy output of agricultural products system increased 19.07×10¹⁵sej after returning farmland to forest(grassland),the energy output of agricultural products in 2006 occupied 3.25 percent of the total energy output which was still lower. In order to improve the dominance of production,the region should attach importance to the coordinated development of various industries.(5) The stability index of agroecosystem in Hanjia tableland is 0.452,it increases to 0.906 after returning farmland to forest(grassland).The results show that returning farmland to forest(grassland) improved the connected network about agricultural ecosystem of the material flow and energy flow, strengthened the automatic control system,regulate and feedback,played a restructuring of agricultural production role.(6)The performance index of System Sustainable Development before and after converting farmland to forest and recovering vegetation is 1.06 and 5.34 in Hanjia tableland.We can see from the data:the economic development level in Hanja tableland is still low and under in the undeveloped economy stage,the result also shows that environment economy system bears low pressure in Hanjia tableland,to some extent the economic development is sustainable in this area. Therefore we should connect with the local resources and develop economy greatly.(7) To the existed problem on effective protection and compensating mechanism caused by returning farmland to forest(grassland),it gives suggestions that puts forward to property rights of returning land to forest,identifies the main benefit subject of ecological services and builds effective value realization mechanism to carry on ecological compensation marketization.