The hilly loess regions suffer severe soil erosion and thus form fragile ecological ecology environments mainly because of their improper land uses and as a result ecological rehabilitation and environmental reconstruction are the strategies for the sustainable ecological and economic developments in these regions. With its simulation steplength standing at one year and its simulation period spanned between 1990 and 2080, the study, relying on the theories in system dynamics (shortened as SD) and feedback control and, has established the SD models of ecological rehabilitation and environmental reconstruction whose 6 modules being respectively aimed at agriculture, forestry, animal husbandry, rural economy, soil erosion and ecological environment. The models have been tested with plus software on PC computer to have an efficiency of 93.5% and can been used for the future simulation predictions.Considering the characteristics of ecological environments and the developmental actualites of agriculture and animal husbandry in the regions, there are three representative models, synchronous developmental model (Model A), progressive adjustment model (Model B) and actual development model (Model C), which have been be chosen for the ecological and environmental reconstructions of these regions in analyzing and predicting the trends in soil erosion, land use, agriculture, forestry and animal husbandry and ecological environment evolution between 2000 and 2080. The simulation results show as follows:
Land use closely relates to the sustainable developments of agriculture, forestry-and animal husbandry, and the degeneration of slope-farmland and grassland degenerations are the main limiting factor in the sustainable developments of agriculture, forestry-and animal husbandry. Thus, properly-regulated land use and accelerated erosion control are capable of enhancing the gradual ecological rehabilitation and the sustainable developments of agriculture, forestry and animal husbandry.
Of the three simulation models, synchronous developmental model is the optimal strategy for ecology ecological rehabilitation and environmental reconstructions in these regions. It can promote the coordinative development of agriculture, forestry-and animal husbandry and help to form a good ecological and economic cycle.
With its good structure and performance, the SD model is capable of the dynamic actions of complex ecosystems involving multiple variables and nonlinear variables thereby becoming an effective tool in the research of ecological rehabilitation. The major problems of the SD model are that because the model covers a large scope and involves some statistically generalized parameter and field experimental data about erosion, which are not completely representative, it suffers in reliability and efficiency and thus needs to further modify the sampling and analyzing methods to guarantee proper parameters and thus make the model perform well.