The Characteristics Of Eco-Factors Under Different Karst Vegetations In The Process Of Succession

The deterioration of ecosystem in karst areas in Guangxi is very serious, which hinders local economic development and environmental improvement, and becomes one of key problems in the province. How to reconstruct the ecosystem is also one of the major projects in Guangxi today. It is necessary to understand the law and mechanism of the succession of karst vegetation. Moreover, we should study the eco-factors in different vegetations in the process of succession. It is available to look for the best way for the rehabilitation of vegetation in karst areas. So far, few studies on the eco-factors have been conducted from the perspective of vegetation succession. In this paper, the main types of karst vegetation in Guangxi, including that of tropical, south sub-tropical, and central sub-tropical are studied. Some characteristics of the major factors, including the soil, the microclimates, the karst water in karst springs and the karst dynamic conditions, are discussed.The research shows: soil organic C, total N and available N increase as succession proceeds, but the tendency is different with the depth. It is significant in layer A, slight in layer B and may even decrease in anaphase. While soil pH value, total K, and available K decrease, but no noticeable trend was found in the case of soil P and available P during the succession. Soil pH value can also increase when soil Ca and Mg increase along the succession series. Because Ca in the soil can be lost and accumulated by the plant, the changes of soil Ca and Mg are complex. The soil CO2 is more complex due to various factors. Progressive succession can improve the physical characteristics of upper layer of the soil: reduce soil bulk density raise soil porosity and water content; but may raise soil bulk density and reduce soil porosity in the lower layer. Although the changes of the chemical and physical characteristics of soil caused by vegetations are obvious during the succession process, they can be affected, positively or negatively, by various factors, such as the habitat heterogeneity.Light intensity, air and soil temperatures decrease while relative humidity increases, and the daily fluctuations become less significant, As succession advances. So the microclimate evolves into a darker, colder, and damper condition and the decrease in fluctuation of the microclimate leads to a more stable environment. In the bare rock stage, the light intensity, air and soil temperatures are the highest, while the relative humidity is the lowest, and the microclimates change violently. It is not suitable for life at this stage. While the light intensity, air and soil temperatures are the lowest, relative humidity at its highest, and the fluctuations are the slightest in the climax community stage. It has stronger ability to regulate the environment and is more suitable for life.With the vegetation advanced, the ability to regulate the karst water gets stronger. And the forest at climax community stage can keep the epikarst spring stable and make it ever-flowing. It is of great importance to solving the problem of water shortage, shortage of drinking water and even water for irrigation, in karst mountain areas. It suggests that the recovery of vegetation is the premise to the restoration and reconstruction of the degraded ecosystem. The chemical characteristics of karst water also change along the succession series. Water pH value decreases just like that of the soil, and the solutes in water increase significantly. The nutriments become easier for the plant to absorb. And it accelerates the cycle of material and the process of soil formation. The dissolution intensity of limestone tablets in soil increases as the vegetation improves; and shows positive correlation to soil CO2 concentration, the amount of soil organic C and N; negative correlation to the amount of Ca,Mg in soil. The succession accelerates the dissolution intensity of limestone tablets in lower layer of soil more greatly than the upper layer. It suggests that better vegetation can produce...