Hydrological Response Of Main Forest Types In Purple Sandstone Regions Of The Three Gorges Reservoir Area

The Three Gorges Reservoir Area is the important national eco-function and eco-fragile area. There forest coverage rate is 51% and types of forest vegetation are various. Studying the hydrological response of forest has great theoretical and practical significance for hydrological process controlling, environmental improvement, expressing ecological function role and so on. Because constitute and biological characteristics of building plant species are different, the forest structure, litter under crown characteristics, soil physical and chemical properties and characteristics of the hydrological response are different. Basing on methods of field test incorporating indoor experiments, combination of actural measurements and the model simulations, traditional and modern equipment, designated testing and dynamic monitoring, biological characteristics and mathematical theory analysis, forest hydrological response of ever green broad-leaved forest, warm coniferous forest, evergreen and deciduous broad-leaved mixed forest, deciduous broad-leaved forest are investigated. Which included studying on hydrological response of canopy, litter and soil layer, establishing index system and using PCA (principal component analysis) for evaluation of forest Hydrological response. The results showed that:Firstly, there is almost no difference in canopy minimum water holding amount among 4 types of forest and the mean value is 1.65mm. The canopy final water holding amount of deciduous broad-leaved forest is similar to ever green broad-leaved forest, is 9.3mm and 9.4mm respectively; the canopy final water holding amount of evergreen and deciduous broad-leaved mixed forest is similar to warm coniferous forest, is14.lmm and 15.6mm respectively. To the average canopy water holding amount, warm coniferous forest (8.42±3.44mm)> evergreen and deciduous broad-leaved mixed forest (6.46±2.84 mm)> ever green broad-leaved forest (5.35±1.91mm)> deciduous broad-leaved forest (5.02±1.97mm). In the same rain type, that canopy water holding rate is diverse among different forest types. When light rain and rainstorm occured, the canopy water holding rate among the above 4 types forest is indifference, average value is greater than 70% or less than 15%, while the average water holding rate is 50% and 30% respectively in moderate and heavy rainfall,, showing significant discrepancy than other 3 forest types.With rainfall amount outside forest increase, the rainfall kinetic energy ascends accordingly. It is positive correlativity of power function between kinetic energy of rainfall and rainfall amount, y=0.0343x1.9296, R2=0.845. The kinetic energy of rainfall under crown from large to small is deciduous broad-leaved forest> ever green broad-leaved forest> evergreen and deciduous broad-leaved mixed forest> warm coniferous forest. On the whole, the kinetic energy of rainfall under crown is smaller than which outside forest. The testing results of the rainfall erosion force shows it is various that reducing for rainfall erosion force by different forest canopy after holding rainfall. On the whole, as the function of canopy holding rainfall, the capacity to reduce rainfall erosion force of warm coniferous forest is the most.Secondly, basing on analysis and simulation to final holding water amount, holding water process and water absorption rate of litter undecomposed and litter decomposed, the hydrological response of litter under crown in different forest types were analysed. The results showed that, to the water holding process of evergreen and deciduous broad-leaved mixed forest, the final holding water amount of litter undecomposed and litter decomposed reach saturation after 2h and 3h respectively, while evergreen broad-leaved forest and deciduous broad-leaved forest are 3h and 5h respectively. When Soaked 24h, the final holding water amount of litter undecomposed and litter decomposed reach steady and maximum. The final holding water amount of litter undecomposed and litter decomposed of evergreen and deciduous broad-leaved mixed forest is 2.61mm and 3.31mm, deciduous broad-leaved forest is 2.39mm and 2.74mm, ever green broad-leaved forest is 2.34mm and 2.54mm, warm coniferous forest is 1.68mm and 2.17mm respectively.In the early soaking term, litter undecomposed under crown of evergreen and deciduous broad-leaved mixed forest is 3.38 mm/h, which is the highest, ever green broad-leaved forest and deciduous broad-leaved forest 2.87 mm/h and 2.59mm/h, warm coniferous forest is 1.70 mm/h. After 0.5h, the water sucking rate reduce severely, and approaching saturation after 3h, with values are 0.04-0.10 mm/h. To the water sucking rate in first soaking term of litter decomposed under crown, ever green broad-leaved forest is 3.39 mm/h and the highest, deciduous broad-leaved forest and evergreen and deciduous broad-leaved mixed forest is 3.08 mm/h and 3.20mm/h, warm coniferous forest is 2.04 mm/h. After 3h, the water sucking rate is approaching saturation, value is 0.03～0.15mm/h. After 6h, reach steady and saturation.Thirdly, the relative analysis results between soil water holding capacity and soil physical properties showed that, soil water holding capacity had positive relations to clay content, capillary porosity, whole porosity, organic matter and>0.25mm aggregate content etc., and negative relevance to sand grains content and density. The relative analysis results between soil infiltration capacity and soil physical properties showed that, soil infiltration capacity had negative relevance to particle content and density, and is positive relevance to capillary porosity and noncapillary porosity significantly. The total water holding content of 4 forest types showed following orders:ever green broad-leaved forest (312.99mm)> evergreen and deciduous broad-leaved mixed forest (302.03 mm)> deciduous broad-leaved forest (279.07mm)> warm coniferous forest (237.64 mm).The first and final infiltration rate of ever green broad-leaved forest is 46.50mm/min and 3.26 mm/min respectively, that is higher than other 3 forest types. The first infiltration rate of deciduous broad-leaved forest, evergreen and deciduous broad-leaved mixed forest is 21.17 mm/min and 24.33mm/min; the final infiltration rate is 2.43 mm/min and 2.92mm/min. The first and final infiltration rate of warm coniferous forest is 10.08mm/min and 1.74 mm/min respectively, that is lowest.Fourthly, based on comprehensive consideration of Hydrological response characteristic with forest canopy, litter and soil layer, considering terrain factors, according to the comprehensive and leading, scientific, regional, and operational principle, selected 38 index, the index system framework for evaluation Hydrological response of different forest types was established by the method of Principal Component Analysis. The comprehensive assessment of representative plant community forest results showed that the Hydrological response in order is ever green broad-leaved forest> evergreen and deciduous broad-leaved mixed forest>deciduous broad-leaved forest> warm coniferous forest.