Study On The Impact Of Freezing Rain And Snow Disaster On Main Hydrological Process Of Three Forest Types Of Dagang Mountain In Jiang Xi Province

This paper, by taking Nianzhu Forest Farm located in Dagang Mountain in Jiangxi province as the survey region, adopts the method of comparative analysis on the relative data between pre-disaster phase and post-disaster phase, including hydrologic function of canopy, hydrological effect of litter layer, hydrological effect of soil and run-off of three forest types, namely, evergreen broad-leaved forest, Cunning ham ia lanceolata and Phyllostachy spubescens stands.The freezing rain and snow disaster has illustrated the influence of three kinds of forest hydrology The research results are shown as follows:1. The freezing rain and snow disaster can cause serious damage to canopy of trees or even death, and lower the canopy density, thus leading to the increased rainfall intensity and rainfall rate within the forest. Compared with the pre-disaster period, the stem run-off rate and throughfall rate is increasing while the rejection rate decreases in the post-disaster period, among which the changing magnitude of stem run-off rate, throughfall rate, and rejection rate of Phyllostachy spubescens stands are the most significant, at 2.1%,2%-3% respectively, followed by the Cunning ham ia lanceolata stands at 0.9%,1%,-2% respectively, while the evergreen broad-leaved forest has the smallest change, at 0.8%, 0.9%-1.8%.2. The freezing rain and snow disaster thickens the lays of ground litter which increases the amount of litter accumulation. For the reason that the water holding capacity of litter related to the hydrological effect and the retention capacity of litter are in direct proportion to the litter volume and thickness, the capacities of water holding and retention are increase correspondingly. The descending order of change magnitude of the maximum water holding arestands stands, Cunning ham ia lanceolata stands, Phyllostachy spubescens stands and evergreen broad-leaved forest increased by 57.23%,33.77%, and 30.00% respectively. The effective water holding capacity of three forest types are about 2.51mm for evergreen broad-leaved forest,2.61mm for Cunning ham ia lanceolata stands and 2.85mm for Phyllostachy spubescens stands, and the largest growth rate of effective intercepting and storing amount are 12.56%,29.85%, and 22.84% respectively.3. The freezing rain and snow disaster makes no effect on the soil bulk density of three-type forest. Both the soil saturated water holding capacity and the capillary water holding capacity have a increasing trend and particularly concentrating at 0-20cm layer of the soil, among which the change magnitude of Phyllostachy spubescens stands are the most significant. There is no change shown in overall soil moisture by seasonal trends while a increasing trend do exist in the soil moisture by diurnal trend, leading to the diurnal variation of soil moisture of evergreen broad-leaved forest, Phyllostachy spubescens stands, and Cunning ham ia lanceolata stands at 3%,2%,1% respectively. The soil moisture content and the rainfall are in significantly positive correlation, in particular in0-20cm layer of the soil while the soil moisture content and the relative humidity are also positively correlated.4. The freezing rain and snow disaster makes great impact on the stability of surface runoff and decreases the underground runoff rate. The advanced peak of single rainfall flow increases the probability of flood and drought, as well as the surface runoff flow of all forest types and soil erosion. The stability of surface runoff is affected most greatly in moderate rain, and the most obvious degradation of forest hydrology performance occurs in Cunning ham ia lanceolata stands, followed by Cunning ham ia lanceolata stands, and finally the evergreen broad-leaved forest.