Eco-hydrological Process Analysis On Forest Ecosystems Of Major Dominant Species In Beijing Mountainous Area

The relationship between vegetation and water resources is the main problem of forest vegetation construction in north China. In this paper, taking Platycladus orientalis, Robinia pseudoacacia, Pinus tabulaeformis and Quercus variabilis, these four typical forest ecosystems as the research object, using the measure data of Miaofeng Mountain to research the hydrological processes of different forest ecosystems of major dominant species and simulate the hydrological processes changes caused by the forest vegetation various, seeks to reveal eco-hydrological disciplines of the different forest ecosystems of this area, to provide the scientific basis for guiding the construction of forest vegetation. The main results are as follows:(1) The ranking of the total throughfall percentage of different tree species during research is: Platycladus orientalis (71.52%)> Robinia pseudoacacia (68.32%)> Quercus variabilis (63.44%)> Pinus tabulaeformis (62.44%); total stem flow percentage is Platycladus orientalis (2.61%)> Quercus variabilis (2.49%)> Pinus tabulaeformis (1.73%)> Robinia pseudoacacia (1.52%); and the total interception percentage is Pinus tabulaeformis (35.82%)> Quercus variabilis (34.07%)> Robinia pseudoacacia (30.16%)> Platycladus orientalis (25.87%). Rainfall quantity, rainfall duration and rain largest intensity within 30min are the important environmental factors of forest canopy rain redistribution. Precipitation outside the forest and inside the forest has very fitting linear positive correlation, canopy interception increase with increasing precipitation. Establish 4 tree species canopy interception model, which has a high accuracy upon examination. The start and end time of rain inside of the forest is generally later than the outside. The correlation between the start time of delayed rain inside the forest and rainfall intensity of the delayed period is more significant, and rainfall outside the forest and one single accumulated precipitation are more relevant. The canopy of Platycladus orientalis has dispersion and aggregation two functions simultaneously to the rain. The ultimate speed of the rain under the forest has been reduced, showing that the forest canopy reduced speed function to rainfall drops. Total kinetic energy of outside rainfall is larger and inside rainfall.(2) The ranking of forest litter total reserves is:Platycladus orientalis> Quercus variabilis> Pinus tabulaeformis> Robinia pseudoacacia. As measured, the ranking of forest litter layer effectively water blocking amount is of Pinus tabulaeformis (12.15t/hm2)> Platycladus orientalis (10.19t/hm2)> Quercus variabilis (7.98t/hm2)> Robinia pseudoacacia (5.40t/hm2). Broad-leafed tree species have better flow and sediment reduction effect than coniferous tree species. The litter type with stronger rainfall interception has stronger evaporation capacity, and the ranking is Quercus variabilis> Platycladus orientalis> Pinus tabulaeformis> Robinia pseudoacacia. Litter evaporation process changes at daytime is a single peak-like distribution, every species of litter evaporation was higher at the daytime than the night. Establish rainfall interception model and daily evaporation model of four litter species, which have high simulation accuracy.(3) Each tree species in sunny conditions, diurnal variation of sap flow rate is a single peak curve trend, sap flow rate of different species changes greater at typical cloudy and rainy weather. Through correlation analysis, it showes that among environmental factors, temperature, solar radiation, VDP, soil moisture and soil water potential and sap flow rate correlate positively, while the relative humidity and sap flow rate correlate negatively. Using the tree sapwood area as the scale transformed middle amount, calculating forest plots transpiration from June to September, Pinus tabulaeformis is 165.28mm, Robinia pseudoacacia is 112.82mm, Quercus variabilis is 218.88mm, Platycladus orientalis is 214.29mm. The ranking of 4 stand shrub total transpiration from June to September is: Pinus tabulaeformis> Robinia pseudoacacia> Quercus variabilis> Platycladus orientalis, which is less than 10% of arbors.(4) The ranking of soil layer total water-holding the depth of different species stands is Robinia pseudoacacia> Platycladus orientalis> Pinus tabulaeformis> Quercus variabilis. Soil infiltration of different species has some differences, coniferous forest soil infiltration capacity is significantly higher than that of broad-leaved forest. During research, of the average soil daily evaporation is between 0.68-1.51mm under various conditions. As to the average soil moisture throughout the growing season, Platycladus orientalis is 15.58%, Robinia pseudoacacia is 15.69%, Pinus tabulaeformis is 15.58%, Quercus variabilis is 15.03%. Main water storage layer of Platycladus orientalis and Robinia pseudoacacia is 20-60cm layer, pine and cork oak is the layer under 40-60cm. 4 kinds of soil moisture receded after rain reflected the dissipatedinfiltration type features. Most of the time within the study period, the soil moisture of different forest tree species in between the medium efficiency water and readily available water, and the ranking of soil water effectiveness status of different forest tree species in study period is:Pinus tabulaeformis> Robinia pseudoacacia> Quercus variabilis> Platycladus orientalis.(5) Use Brook90 lumped hydrological model to describe a typical plot of forest eco-hydrological model, by two years measured data on soil moisture calibrating and testing model parameter to make the model achieve high simulation accuracy. With 2001-2010 meteorological data simulated 4 kinds of eco-hydrological process in forest ecosystems, analysis of its characteristics of the input precipitation distribution, characteristics output evapotranspiration and forest runoff characteristics. According to Model simulations, it shows that average ecological water demand is of Quercus variabilis(954.1mm)> Platycladus orientalis(811.0mm)> Pinus tabulaeformis(498.4mm)> Robinia pseudoacacia(420.1mm). When setting the ecological water demand was 90% and 70%, the corresponding value of stand LAI and canopy density are the optimum vegetation carrying capacity of water conservation forest and the soil and water conservation forest, simulation calculated the vegetation species carrying capacity range of the water conservation forest and soil and water conservation forest main building group in Beijing mountainous area.