The Temporal And Spatial Variation Of Effective LAI Of The Water Conservation Forest And Water Effect Research In Du Watershed

Protecting the quality and quantity of the source water in the large-scale water diversion project has aroused widespread concern. The water conservation forest area and structural change surrounding this project affect water quality and quantity issues in the region by influencing the regional land use cover change. Meanwhile, water conservation forest through the canopy rainfall interception, ground litter soil moisture storage and transport and other specific ways to participate in regional rainfall redistribution process, but also an important regional hydrological model input parameters.In this study, we chose one of the important sources of runoff in Danjiangkou reservoir area as the water resource of the South-North Water Diversion Project-Du watershed as the research object, the study area is located in Hubei Zhushan Du River to the confluence of the Han River, with a total area of3433km2.In the study area, select the typical water conservation forests, selection Hemiview canopy analyzer to collect the effective LAI data in the basin. Combined with remote sensing data estimating LAI in the region to establish an empirical model, and use this model monitored from1990to2010in the area of water conservation forest dynamics. Then establishment of a basin water conservation forest canopy interception model to estimate the area of water conservation forest canopy interception capability and spatial distribution. Meanwhile in Pinus massoniana forest, cedar forest, oak tree and mingled forest collecting litter-fall samples and soil samples:Each forest,10m*10m range, randomly collected20cm*20cm litter-fall samples10;100ml samples of soil cutting ring5, and to study the water holding capacity of the ground cover and soil layer. The main conclusions are as follows:(1) Using the classical vegetation indices and ground LAI data, empirical models established in several water conservation forest to estimate leaf area index in the Du watershed. And find the power function model based on NDVI data have the highest correlation coefficient, determines the highest (R2=0.63).Using the empirical model of TM image of1990,1999and2010are estimated, separately calculated the image of leaf area index of three years of Du watershed. Comparative analysis shows that, plugging water conservation forest effective LAI in Du watershed of2010with an average value of 2.82; in1999the average value of2.08; in1990the average value is1.61, the growth rate is respectively28.8%and35.6%.(2) Based on the estimation model of basin LAI and according to the empirical formula to estimate the maximum interception by canopy in Du watershed. Four kinds of typical forest canopy interception as follows:the cedar forest(0.84mm),mingled forest (0.83mm),oak trees (0.80mm),Pinus massoniana (0.71mm).Interception statistic analysis to the whole river basin, the basin average interception is1.01mm. The results showed that canopy interception, Zhangwan and Yunxian was significantly less than Maojian District, Fang County and Zhushan. The largest canopy interception in Du watershed is2.62mm, the average retention capacity of1.01mm and the standard deviation is0.31.(3) Through the TM image interpretation of the1990s,1999s and2010s,then through field surveys to extract water conservation forest area. The results showed that in1990,1999and2010, the area of water conservation forests, respectively,2075km2,2461km2,2677km2,the water conservation forest area increased18.60%and8.76%respectively.(4)By the water holding hand, analysised with the volume, maximum water holding rate, the maximum water holding capacity and other physical properties, draw the following conclusions:in the volume of litter layer, mingled forest(73.75t/ha),Pinus massoniana(42.50t/ha),oak trees(35.00t/ha),cedar forest(28.75t/ha);Maximum water holding capacity has a positive correlation between the degree of decomposition, ground cover stock volume and the largest water holdup. Decreasing order, mingled forest, cedar forest, Pinus massoniana, oak trees; cedar forest has the maximum water holding rate and reached a maximum of155%, followed by Pinus massoniana150%,96.30%mingled forest, oak tree96%.(5) In soil water storage capacity, analyzed four kinds of forest water holdup on the difference in non-capillary porosity and non-capillary. Average non-capillary porosity largest cedar forest, was4.78%, followed by oak tree (3.76%),Pinus massoniana (2.56%), mingled forest(1.74%), of which the largest is the coefficient of variation Pinus massoniana (74.00%). In soil water-holding, cedar forests has the best hold water effect.