Effects Of Forest Vegetation Structure On Rainfall Input Process In Beijing Mountainous Area

Research on how forest vegetation to regulate the mechanism of rainfall input process is the basis of typical forest ecosystem structure and hydrological process. Through locating observation at JiuFeng ecological station, this article get to understand the effects of forest vegetation structure on both vertical and horizontal level to rainfall input process. The influence of forest vegetation to rainfall redistribution was analyzed vertically through four levels of Joe, irrigation, grass and litter, and through the mainly factors on horizontal level as leaf area index, crown density and biomass, the main research results are as follows:(1) The main rainfall type in Beijing mountain area is the rainfall of0～10mm, but the contribution rate of this type of rainfall was not the largest. The rainfall intensity is mainly controlled by precipitation and rainfall duration; As for the four tree species, orientalis, quercus variabilis, pinus tabulaeformis, robinia, there is a good linear correlation relationship between the precipitation outside and inside the forest,so as to stem flow, canopy intercept rainfall quantity.(2) Factors on the horizontal level of the forest vegetation, the leaf area index, crown density, shows good linear correlation with canopy interception for the four tree species, orientalis, quercus variabilis, pinus tabulaeformis, robinia. While the the factor of biomass estimated by tree height and diameter at breast height data presents positive correlation with forest canopy intercept rate, but the linear correlation coefficient is not high.(3) The forest vegetation canopy will change rainfall characteristics:the start and stop time will be delay, the raindrop size will be bigger by the gathering effect, the terminal velocity of raindrops will be cutting, the raindrop kinetic energy will be increased.(4) The intercept observation devices for shrub and litter using in this experiment have improved to be effective, as the canopy interception rate of the shrub layer has a good index correlation with rainfall outside the forest and the canopy interception rate of litter presents good logarithmic relationship with rainfall outside the forest. The intercept observation devices for grass designed by bare soil contrast method, is theoretically feasible, but the blockage of drainage holes in soil is found to be unsolved problems in practical application. Further study should extend the observation time to find the effective ways to adopt the device.(5) The total canopy interception by four layers on vertical levels of the four tree species, orientalis, quercus variabilis, pinus tabulaeformis, robinia, distributed between37%～37%, and the order of canopy intercept quantity for four layers on vertical levels is tree layer> shrub layer> litter layer> herb layer.(6) The simulation effect for canopy saturated situation intercept is far better than the unsaturated situation by the improvement Gash model with the crown density factor; and the simulated values and measured values show a good linear relation, which proved the Gash model has good applicability in the study area.