桂西北喀斯特石山区石漠化产生的地质背景及治理措施研究

Study on geologic background of northwest Guangxi karst rocky desertification and fathering measures

通过对桂西北的都安、东兰、巴马、凤山、乐业等县的地质、地貌、土壤和植被野外调查研究以及对岩石和土壤的采样、分析表明,桂西北喀斯特石山区的碳酸盐岩类总体上可分为可溶性较强的石灰岩类和可溶性较弱的灰质白云岩类。石漠化程度与地质背景条件的差异有关。石灰岩类的酸不溶物含量(1.7%)比白云岩类的(2.2%)低,对成土不利;前者的pH值为8.4,而后者的pH值为7.36,这种差别导致前者的植物种类和生长高度都不如后者;穹隆状背斜构造以及断裂裂隙发育地带不利于水土保持和植被生长;峰丛地貌的锥峰地段以及地形坡度大于45°的陡坡地段的土壤和植被盖度一般均低于坡度小于45°的地段,坡度与土壤盖度和植被盖度通常为负相关关系。根据这些差异性,针对性地提出了在不同地质背景条件下防止石漠化发生的治理措施。

Field survey in geology, soil and plant, as well as analysis of rock and soil samples from Du＇an, Donglan, Bama, Fengshan and Leye counties in northwest Guangxi indicate that carbonate rocks can be gen- erally classified into two types of limestone and calcareous dolomite. The desertification intensity in the hill area of karst formation is related to the differences of the geologic background. The limestone is disadvantage to the formation of soil for its lower, 1.7%, indiscerptible composition content comparing to dolomite with higher, 2.2%, indiscerptible composition content. Average pH value of the calcareous soil is 8.4 and 7.36 for the limestone soil and the dolomite soil respactively, which results in some differences in growth of plants. Anticline as dome shape and development of faults and fissures are also disadvantage to keeping soil and growth of plants. The coverage density of soils and plants in the peak part of the series of peaks land- form and on steep slope with slope gradient more than 45 degree is generally lower than that on gentler slope with slope gradient less than 45 degree. Slope gradient shows negative correlativity to coverage density of soil and plants. Based on the differences of geologic setting, some fathering measures are pointed out for preventing further karst rocky desertification.