| Grain for Crop Project (GCP) is one of the ecological projects which have largest venture size,vide covering and complex process in China. GCP had achieved some ecological benefit for now. How to consolidate achievements was project's emphasis at present. For farmers'livelihood who had returned farmland and consolidating achievement ,economic development of GCP was crucial .For GCP harmonious,healthy and sustainable development ,it had important significance to deploy forecast and analysis about GCP economic development.Using Hebei Province as case, adopting household survey and informal discussion, according to actual situation of GCP progress in Hebei Province, and applying System Dynamic (SD) principle and software of VENSIM, this paper created economic development SD model of GCP in Hebei province, predicted the economic development trends of the main GCP afforestation tree species .According to the afforestation situation ,divided the SD model into economic forest,larch wood and poplar three sub-module. From extensive to precise, set multiple management models , run simulation and adjusted many times, optimal selected five models which had representative in management level ,then analyze the economic development status of the three afforestation tree species in different models .According to its production characteristics , this paper divided the economic forest into before,in and after harvest seasons three stands. Using statistical comparison methods , analyze the economic forest sub-module development trend in different models. As GCP afforestation areas accumulated at first then the GCP stage ended, and the economic forest had a grow-renewal press, both of their economic benefits in different models had an increase-reduce-steady trend. Results showed that, models which had higher management lever had higher development lever . The economic forest development lever of models which had higher management lever ,as model 1 and model 2,were higher than those of models had lower management lever ,as model 3 and 4, and model 5 which had extensive management. In the model 1 and model 2, through improving stand survival rate,timing advance and prolonging fruit bearing time and improving product quality, the economic forest developed quickly, and kept on a high development lever.This paper selected larch and poplar as represents of timber forest, according to GCP afforestation situation in Hebei province . And divided poplar into poplar-timber forest and poplar-seedling forest .Divided the timber forest into four stands ,young stand, middle age stand,near-mature stand and mature and over-mature stand. Comparatively analyze the prediction results of each variable in the two sub-modules ,the study results showed :For timber economic benefit only correlated with harvesting volume and timber quantity , the timber economic development trend had high correlation degree with mature and over-mature stand volume. Both larch and poplar timber forest economic development had a increase-reduce-stable trend .Larch and poplar timber forest reached their highest lever in 2078 and 2065 , respectively. The comparative result between models ,from high to low, was model 1 ,model 2, model 3 ,model4 and model 5. Since renewal the died stand in time ,the total volume had no much difference. Forest in model 5 which had extensive management did before mature , spent a lot manpower and financial resources ,while had litter economic benefit. So in future, the timber revenue couldn't paid renewal need .For poplar-seedling had a shorter grow-period ,and can quickly renewed , it had remarkable nearly benefits. Poplar-seedling reached the highest lever about 2010 in the five models , kept on a steable development after 5 years.Larch and poplar timber forest had a same development trend .Since poplar had a short grow period and got mature quickly ,so its volume changed rapidly and earlier. During the predicting time, in the same model ,the annual earnings of poplar-seedling was about ten times of that of poplar timber. Shortening the grow period ,improving the product value , can improve the forest development lever. The feature of poplar seedling marketing was that quickly renew took markable nearly benefit. The seedlings were planted densely , if not renew in time , the seedlings would dead a lot by fighting for living space.The total economic benefit development trend of GCP afforestation had an increase-slowly introduce–slowly increase-keep steady trend. This trend had highest correlation degree with poplar forest , which had short grow period and largest afforestation area . The comparative result of total economic benefit between models was the same with that of timber forest. The total economic benefit reached higest lever in 2012, then gradually introduced after 2012, and reached the lowest lever in 2022, then slowly increased and kept steady.Through building a SD with reasonable structure model in which variables'collection were accordance with actual situation, this paper predicted and analyze based on predecessors'study results ,got some results and found some problem, raise some advise ,had reference value for GCP study in future. |
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