CANOPY RESISTANCE AND LATENT HEAT EXCHANGE IN A CORK OAK STAND

摘要

Cork oak stands in Portugal are sparse and located mainly in the southern county of Alentejo. Those canopies exert a protective environmental role, needed by the prevalent conditions of Mediterranean climate with harsh hydric and micrometeorological stresses, derived of the high Summer temperatures, water vapor deficits and associated to soil erosion.The Penman-Monteith equation allows a quantification of contributions of some key factors that control canopy evaporation, mainly available energy, canopy and aerodynamic resistances and the atmosphere humidity deficit. The inversion of Penman-Monteith,using values of evaporation obtained by eddy covariance is also a common method for calculating canopy resistance, rc. Eddy covariance data of friction velocity and wind velocity are used for calculation of the aerodynamic resistance, ra.An algebric manipulation of that equation by Jarvis ef al. (1986) resulted in the introduction of the decoupling dimensioneless coefficient E2, representative of the coupling between vegetation communities and the atmosphere, defined as: