The Simulation And Prediction Of Karst Rocky Desertification Based On Cellular Automata

Rocky desertification of karst mountain region in Sourthwestern China is one of the most important regional environmental problems in Western China. Current researches on Rocky desertification are excessively concerned with factors inducing rocky desertification, methods evaluating the local karst environment, the measures recoverying ecosystem, but especially neglect the researches on mechanism and spatial structure of rocky desertification. This Dissertation focuse on the problems in the study of Karst rocky desertification, and try to develop a simple and effective mathematical model to simulate and predict the karst rocky desertification based on the natural and human factors leading to the development of desertification. The ecological process of surface cover that affects the karst system was also integrated into KarstCA models, such as colonization, plant death, land degradation and soil formation of rock. According to random characteristics of cellular automata, such transitons between the vegetation-bare soil-bare rocky were made in certain probabilities. Then a cellular automata model based on ecological processes of karst rocky desertification was established. KarstCA model can simulate the spatial and temporal development and evolution of desertification in karst systems according to a simple neighborhood rules to generate complex spatial pattern. This model considers configuration of neighborhood characteristics from three aspects from a variety of factors acting on different scales.KarstCA model can be used to simulate the natural and human factors,and only the scenarios of natural factors,to explore characteristics of land cover changes of karst system, which contributes to quantifying natural and human factors on the development of desertification. Then the author further explored spatial and temporal characteristics of rocky desertification under the scenarios of the different intensity of human activities and the different cell size, and tested the robustness of KarstCA model. Finally, the author discussed the experience of the critical threshold characteristics of rocky desertification in karst system combining with the existing research literature and penetration theory. The main conclusions of this study include:1)73.4 percent of the results of KarstCA model simulation were correct considering the natural and human factors.While 56.7 percent of the results were correct when only considering the case of natural factors. It was found in further study that the trend of bare rock was negatively related to the vegetation patch area while it amounted to more than 54 percent and continued to increase,2) The impac tof human activities on vegetation in the karst system was mainly positive effect since 1992. Different human activities significantly affected the vegetation patch characteristics. They all initially presented a heterogeneitious trend with the ongoing human activity, and then tended to become homogeneity,3) Cell size has some effects both on the spatial pattern of KarstCA model and system stability. The effectiveness of vegetation patches-area power function, as an indicator of the development of desertification, needs to be further studied.