Abstract: Based on the radiosonde data in the agroforest area in Huang Huai Hai plain, a simplified one dimensional model was established to study the momentum, heat and water vapor fluxes above the agroforest ecosystems with three different structures. It was found that because of the frictional effect, the wind velocity above the vegetation canopy increased with height rapidly, which caused an insistent downward momentum flux above the canopy. During the stable clear night, the momentum flux was significant because of the strong wind shear. It becames weak around noon,as the strong turbulence made the vertical wind shear smaller. Both heat and water vapor flux went downward in the night, which caused respectively by the radiation cooling of the vegetation canopy and by the water vapor condensation in the very low level. The heat flux turned upward after sunrise because of the surface heating, which reached to the maximum at noon when the surface super adiabat formed. The water vapor flux turned upward as well, due to the high vapor content in the lowest level caused by the evaportranspiration of the vegetation canopy at day. The author also discussed the flaw of one dimensional model and revealed some important aspects of atmosphere biosphere interaction.

Key words: Agroforest ecosystem, Turbulence flux, Mixing length, street canyons, diffusion simulation, air quality, development trend