Water Movement Process And Mechanism Analysis On Forest Ecosystems In Beijing Mountainous Area

The relationship between vegetation and water resources is the main research problem for a long time. 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) In 2008-2015, annual rainfall is about 539.64 mm in Beijing mountainous area, slightly lower than years of average rainfall (580 mm), precipitation relative change rate and the coefficient of variation is small. In less than 30 mm of rain or windy (80%) of the year events; But the largest contribution to the annual precipitation of heavy rain and heavy rain (50% of annual precipitation); Horizontal precipitation is mainly composed of condensation water of plant and soil surface and adsorption water for soil surface. Soil adsorption of water was produced in growing season and condensation water was produced in non-growing season. The amount and days of horizontal precipitation in non-growing season was higher than growing season. The relationship between horizontal precipitation and air temperature, soil temperature and wind speed were negative relation. The amount and days of horizontal precipitation for grass was higher than forest; Broad-leaved forest was higher than coniferous forest; the holding water of the broad-leaved forest was higher than coniferous forest. But for soil infiltration capacity, coniferous forest was higher than broad-leaved forest. Soil unsaturated hydraulic conductivity was influenced by soil water content, soil texture and structure. The soil water content was decrease with depth increase and it exist hysteresis. Soil water deficit was produced in 80 cm soil layer and it is obviously for coniferous forest. The soil water potential had the same rule with soil water content consistent.(2) For the rates of sap flow and transpiration, it was increases firstly then decreases in sunny days. It exsit strong correlations among transpiration, air temperature, solar radiation, VPD, soil water content and soil temperature. Transpiration in growing season was significantly higher than the growing season and broad-leaved forest was higher than coniferous forest. The daily value of soil evaporation was in between 0.68～1.51 mm and it was higher than litter evaporation. But it was belower than plant transpiration. Daily soil evaporation of no litter cover was higher than litter cover. It exsit strong correlations among soil evaporation, relative humidity, VPD, precipitation, solar radiation, but it was weak correlation among wind speed, soil water content and soil temperature. In sunny day, it was bimodal curve for evapotranspiration variation. In growing season, the evapotranspiration was greater than the non-growing season. Evapotranspiration of non-growing season was stable than growing season. It exsit strongly correlations among air temperature, canopy net radiation, soil water content and relative humidity.(3) In the growing season, water storage was decrease with time and it was opposite rule for non-growing season. Water storage of coniferous forest was stable than broad-leaved forest. Under the condition of rainfall, soil water storage appears to increase gradually and water seepage to deep soil layer. When soil water storage reached constant value, it presented down trend. This phenomenon exist hysteresis with soil deep. Monthly value of soil water storage was mainly focus on between 15～30 mm. It was fluctuated remarkably in June, July and August. For the lower soil layer, water storage was around 20 mm. At the start of the precipitation, water storage in root region was increasing and water seepage to deep soil layer. In this period, net water storage was negative value. Soil water storage in summer and fall was greater than winter and spring. Root region water storage of coniferous forest was stable than broad-leaved forest. For mant years, water income equal to output in this region. Soil water was maily water income. Water income in growseason was higher than output and it was opposite rule for non-growing season.(4) Forest canopy structure regulates and control for water sports. The variation of canopy stomatal conductance and atmospheric water vapor channel regulation coefficient were consistent with the change trend of transpiration and it was increases firstly then decreases. Monthly variation of two parameters was not significant difference. In growing season, two parameters were greater than the non-growing season and broad-leaved forest was higher than coniferous forest. It exsits strong correlation among canopy stomatal conductance, temperature, relative humidity, VPD and but it has a certain limit. For atmospheric water vapor channel regulation coefficient, wind speed and VPD is the main influence factors and showed a good correlation and difference.Canopy stomatal conductance and atmospheric water vapor channel regulation coefficients response of transpiration by linear positive correlation; Temperature, vapor pressure difference and water use efficiency (wue) is linear positive correlation. There is a logarithmic relationship photosynthetic active radiation and water use efficiency.