The Characteristics Of Eco-hydrological Effect Of Different Forests In Beijing Mountain Area

Ecological benefits of vegetation should be taken as the main goal of forest management in Beijing and surrounding areas.Taking Pinus tabulaeformis, Acer truncatum, Platycladus orientalis, Cotinus coggygria forest ecological systems were taken as the research objects in Beijing mountainous region. The forest structure characters of different stands and hydrological process of different hydrological function layers were invested. The relationship between WUE and forest structure was discussed based on field monitoring and simulation methods, and a forest management medel on the base of WUE was build. We hope that all the foundings in this study that are conducive to greening work in the region. The main research results are as follows:(1) The carbon stock of Pinus tabulaeformis stands was found increased with increment of forest density, and the relationship between carbon stock and forest density can be expressed as following, CS(ubac)=-0.00002FD2+0.1427FD-27.648, CS(adret)=-0.00002FD2+0.0794FD+7.2556, in these curves, the corresponding forest densities of the apexes were 3568 stem/hm2% 1985 stem/hm2 respectively. F’or Acer truncatum stands, the relationship between carbon stock and forest density can be expressed as following, CS=-7E-05FD2+0.2563FD+74.594, in the curve, the corresponding forest density of the apexes was 1830 stem/hm2.(2) Under the condition of different forest stands, the percentage range of trunk runoff in rainfall is 2.01%-7.07%. With the regression analysis, the stand tree trunk runoff and rainfall followed a significant linear relationship (p<0.05), and there is a multinomial regression equation between trunk runoff and rainfall amount in Acer truncatum stands. The corrected Gash model was used to simulate forest canopy interception amounts of different stands, the result shown that the water-holding capacity of canopy increased with increment of forest density.(3) There is no significant different amount forest litter amount of most invested stands which were set on same slope side and with same species. The results also shown that the forest litter amount increased with increment of forest density, the forest litter amount on the adret is bigger than the one on the ubac. With a rainfall simulating experiment, interception of litter were found it can reached virtual interception when rainfall reach 35mm-45mm, and the ratios of virtual interception to maximum WHC is steady, and the ratios can be used to estimate virtual interception.(4) Under the conditions of different stand density, the runoff is positively correlation with rainfall, In the thick stands, the increasing speed of runoff while the increment of forest density were higher than that in the thin stands. The standard SCS-CN model was used to simulate runoff with different site conditions. During the simulation, the water moisture, LAI, forest density, caver rate, slope were consided and reflected in parameter CN. With model test result shown that the accuracy of the improved model of SCS-CN is significantly improved.(5) This study adopted a ecological hydrological model-Brook90 to simulate different forest stands’ hydrological processes. With the parameter adjustment and model testing, the the absolute error of average moisture content of different forest soil layer were within ±5%, the relative error were within 20%, the results were acceptable. The simulation results show that there was a significant difference between water banlance situations under the condition of rainfall during the growing season, and the results shown that the evapotranspiration was the most important form of rainfall distribution in forest stands, and runoff is the minimum part.(6) With increasing of forest density, the WUE of Acer truncatum stand increased firstly and then decreased. With a forest density of 1600 stem/hm2, the WUE of Acer truncatum stands reach the maximum value, followed by Pinus tabulaeformis and Platycladus orientalis stands. The proper forest densities were presented with a more efficient carbon sequestration for different tree species.