A Study On The Ecohydrological Processes And Water Balance Of Pinus Sylvestris Var. Mongolica Forest In Northern Daxingan Mountains

The ecohydrological processes and water balance of Pinus sylvestris var. mongolica forest was studied in northern Daxingan Mountains. We observed the canopy interception, litter water-holding, water storage of soil, the transpiration of canopy and soil evaporation, to reveal the relationship between Pinus sylvestris var. mongolica forest and hydrological effect, and mechanism of hydrology and ecology. We hope to enrich and develop the coordination forest vegetation construction and management theory and technology between the forest vegetation and water resources management in arid and semi-arid area. The results showed that:(1) The canopy interception rate was 22.08±5.51% of the Pinus sylvestris var. mongolica forest and with a logarithmic relationship of the rainfall precipitation. The throughfall accounted for 77.12±5.70% and with obvious linear relationship of the rainfall precipitation. We can use its relationship to establish model to simulate the throughfall of the forest. The stemflow accounted for 0.80% of the rainfall precipitation and increases with the increasing trunk diameter level. Using the revised Gash model to simulate the canopy interception in 2013 showed that the simulation value was 7.24 mm lower than the measured value and the relative error is 7.97%. The revised Gash model can better simulate the canopy interception loss in the Pinus sylvestris var. mongolica forest of northern Da xingan Mountains.(2) The soil moisture content of 0-20 cm soil had obvious seasonal changes along the seasonal change tendency with the precipitation. The soil moisture profile of vertical distribution characteristics showed that the depth of soil water utilization is about 30 cm and the soil moisture content changed intensely up of the depth. The per unit area of water storage capacity of the Pinus sylvestris var. mongolica forest was 1183.99±212.98 t/hm2. The soil in the Pinus sylvestris var. mongolica forest is generally thin, and with the stone grain of schist below more than 30 cm. The roots of the plants are mostly concentrated in the 0-30 cm soil layer.(3) Canopy transpiration is one of the main ways of the moisture dissipation, and is accounted for 44.52% of total rainfall precipitation throughout the growing season in 2013. The transpiration water consumption rate is 1.31 mm/d. The sap flow started at about 5:00 in the morning, and the maximum and minimum average value of the sap flow rate was the highest in the sunny day and lowest in the rainy day. The sap flow in the night is accounted for less than 10% throughout the day. The sap flow width became narrow with the decrease of the diameter level. Correlation analysis results showed that the main environmental factors affecting the sap flow density was solar radiation and followed by the vapor pressure deficit, air temperature, air relative humidity, wind speed, soil temperature and soil moisture content of 20 cm soil layer.(4) The water consumption of forest land evaporation accounted for 19.27% of the total rainfall in growing season 2013. Regardless of shrubs and litter, the daily change of forest land evaporation showed a trend of decrease after the first increase. With increasing of the month and time of sunrise, the evaporation peak was ahead of the time. The soil with shrubs and litter can hold the water better. The result of correlation analysis showed the main environmental factors affecting the forest land evaporation was saturated vapor pressure, soil temperature and solar radiation.(5) Through the water balance analysis, although there is a water deficit situation between different months, but the water balance can achieve in growing season 2013. The groundwater was not consumed by the Pinus sylvestris var. mongolica forest, and with a surplus of 31.12 mm can supply the river runoff. The proportion of each component of water balance is:the interception by canopy (20.23%), litter holding (8.71%), canopy transpiration (44.52%) and forestland evaporation (19.27%), soil water storage (0.34%), leakage and underground runoff (6.93%).(6) As the climate changes, evaporation and rainfall precipitation will appear unbalanced phenomenon, and with the time goes on, the contradiction between the precipitation and evaporation will be more sharp, then an adverse effect will appear on the growth and survival of Pinus sylvestris var. mongolica. Due to the strong evapotranspiration ability of the Pinus sylvestris var. mongolica forest (84.02%), development of the Pinus sylvestris var. mongolica forests have a reduced effect on runoff contribution. From the perspective of natural Pinus sylvestris forest, climate warming will make the Pinus sylvestris var. mongolica forest water deficit due to higher evapotranspiration and so that the population distribute northward. Explore other forest management measures to reduce the evapotranspiration of the forest and maintain the sustainable development of forest ecosystem in northern Da xinggan mountains is an important breakthrough of future research.