Prime Farmland Protection Zoning Based on Bayesian Network
2016, 31 (6):
Basic farmland protection zoning is the key issue of implementing land protection and ensuring food security. At present, most of the related studies on farmland protection zoning are based on the evaluation of the suitability of cultivated land, with no consideration of the change process of cultivated land in the past. Therefore, they cannot ensure the zoning result to adapt to the trend of cultivated land change, leading to the prime farmland being frequently occupied and adjusted. To guarantee the stability of prime farmland as well as its cultivation quality, we put forward a method of zoning farmland based on Bayesian network (BN) model in this paper, which includes both factors concerning cultivated land suitability condition and its dynamic change. With data of land use status in Daye City at two time points (1997 and 2012), the factors about suitability and changes of cultivated land are obtained. Suitability factors are used to reflect the quality of cultivated land, and the factors about changes are used to study the change disciplinarian of cultivated land. Using the basic farmland potential as the target variable, we defined the structure of the network by expert knowledge. The BN was trained by Maximum Likelihood Method with 57 085 random sample points. The results show that, only 60% farmland in Daye City remains stable from 1997 to 2012. In the three dynamic factors, the influence of building occupancy is the greatest, which accounts for 28.2%, followed by the internal adjustment, 17.4%, the influence of ecological footprint is the least, which accounts for 4.65%. The results of sensitivity analysis also indicate that building occupancy has the greatest influence on the potential value of the prime farmland, with the highest variance reduction of 26.8%. The variance reductions of the distance to the center of city (0.43%) and the center of the town (0.58%) are greater than that of the distance to the road (0.14%) or the railway (0.28%), reflecting that urban expansion has greater impact on the occupation of basic farmland than transportation construction. In natural condition factors, the influence of the distance to the water area is the minimum, which is less than 0.02%, while soil erosion has the greatest variance reduction of 0.34%. It can be deduced that soil erosion, but water, is the most important nature factor to destroy the stability of cultivated land in Daye City. Then, using the values of suitability factors in 2012, we obtained the relative potential value of each cultivated land parcel as the prime farmland through forward reasoning of the trained network, and zoned the farmland with the potential value of the target variable. The results show that, compare to traditional land evaluation method, the zoning model based on BN can improve the stability of agricultural value and ensure the quantity and quality of prime farmland. It is a new and effective model for farmland protection zoning.
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