| The implementation of the Grain for Green Project in hilly gully region of the Loess Plateau has achieved remarkable results. The practice shows that the key to the successful implementation and consolidation of the project is ecological compensation of the returning farmland to forest. Quantitatively formulating compensation standard is a core and difficulty to establish ecological compensation mechanism. In order to explore appropriate compensation standard for farmland returning to forest and provide reference for national and regional compensation policy formulation in the Loess Plateau, this paper is under the international background of the Clean Development Mechanism and logging ban policy to build a dynamic model of compensation standard for farmland returning to forest by combining value of carbon-sink with the farmer’s opportunity cost. Through theoretical analysis and field measurements, combined with laboratory experiments, we made an empirical analysis on the Loess Plateau selecting representative watershed—Xiannangou. The main results are as follows:1. Dynamic model of compensation standard for farmland returning to forest based on carbon sink have been builded. Using ecological economics theory such as joint production, externality, utility theory of value, etc, combining reality basis for carbon sink calculation and the development of carbon sink trade market, considering fully the interests and selection of the compensation bodies and compensation objects, we think it is feasible and operable to compensate peasant households who gave up farming and planted grasses or trees based on carbon sink so that the positive result of Grain for Green Project can be maintained. Based on above analysis, building dynamic model of compensation standard for farmland returning to forest by combining Value of carbon-sink with the farmer’s opportunity cost is (In the relational expression:S(t) represents for the compensation standard of t years after farmland returning to woodland, FVst represents for the carbon sink final value, FVct represents for the opportunity cost final value), among them, (In the relational expression:△b(t)represents for annual incremental carbon sink, Pb represents for the price of carbon sink, r represents for interest rates); (In the relational expression:m represents for crop species in slope cropland,0 represents for crop yields, P represents for crop prices, C represents for economic investment for crops, j represents for each crop economic input types, A represents for planting area,I represents for multiple crop coefficient, Cf represents for costs for afforestation).2. The carbon sink of farmland returning to forest ecosystem in Xiannangou watershed have been calculated. Using way of "spatial sequence instead of time series", we have measured diameter at breast height and tree height of robinia pseudoacacia for 10 years,11 years,12 years,13 years,14 years,15 years,16 years,19 years,20 years,25 years,33 years,38 years,39 years. The tree height fits with vegetation restoration years and diameter at breast height fits with vegetation restoration years. The richard equation is choosed to fit growth model after synthetically contrast goodness-of-fit and tree growth trend. The result of fitting curve are as follows. Acacia DBH growth model is: Acacia high growth model is (In the relational expression:t represents for tree-age; D represents for diameter at breast height; H represents for tree height). Acacia DBH and tree height growth model unite with the allometric growth equation and carbon content of acacia different parts to calculate acacia plant carbon sinks. Soil organic carbon density is calculated by measured soil organic carbon content and soil bulk density of 0-100 cm soil layer thickness for slope cropland, Returning farmland for 11 years,13 years,15 years,16 years,20 years,39 years. Soil organic carbon density fits with vegetation restoration years. The best goodness-of-fit is exponential function. Soil organic carbon density Changing over vegetation restoration time can be expressed as: y=22.513e (R2=0.980). Measured grass layer and groundlitter layer carbon sink account for the entire forest ecosystem carbon sink ratio is very low, less than 5%.3. Empirical analysis of compensation standard for farmland returning to forest in the Xiannangou Watershed. The compensation cycle is determined to have 35 years according to the growth characteristics of the robinia pseudoacacia forest in the Xiannangou Watershed. The compensation process and standard are divided into two stages:farmland returning to forest between 1 to 13 years, the farmer’s opportunity cost is greater than the value of carbon-sink, we should compensate for the actual economic loss of the farmers. Executable standard of compensation for farmland returning to forest is 1909.17 yuan/(hm2·a), through calculation of the opportunity cost; farmland returning to forest between 14 to 35 years, value of carbon-sink is greater than the farmer’s opportunity cost, it means that industry substitution has been completed. Executable standard of compensation for farmland returning to forest is 3650.65 yuan/(hm2·a), through carbon sink model calculation. In summary, the value of carbon-sink accounts for 89.50% of the total compensation in the compensation period. Artificial robinia forest will gradually generate shrubs and decline after the compensation period, therefore, the compensation standard should be calculated and perfected again in accordance with the change of forestland ecological community after the end of the compensation period. The value of carbon-sink is involved into the compensation system, it can induce farmers to enhance performance of forestland management and protection consciously for improving the carbon sink production, which is beneficial to perfect compensation system of the Grain for Green Program in the Loess Plateau.4. Ecological compensation mechanism of returning farmland to forest has been constructed based on carbon sink, including compensation standards, compensation bodies and compensation objects, ways of the compensation, the capital source, monitoring technology of carbon sink and organization guarantee. The evolution of the compensation mechanism has been analyzed. Compensation standard based on carbon sequestration is a minimum standard of compensation in consideration of ecological service function value of forest from conversion of cropland. Compensation standards will increase when other public ecological products of positive externalities are sufficiently scarce and have international community recognized measurement methods and trading market. After the carbon trading market enoughly mature and perfect and farmers master the carbon sink trading mechanism, the approach of compensation can realize successful transition from government compensation to market compensation and compensation bodies will shift by the government for carbon emitters. |
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