Micrometeorological conditions and canopy energy exchanges of a neotropical rain forest (Surumoni-Crane Project,Venezuela)

Vertical profiles of air temperature, humidity, wind speed and photosynthetically active radiation were examined systematically within and above a primary Amazonian rain forest in Southern Venezuela. During daylight hours the observed gradients of temperature and humidity suggest that turbulent mixing between vegetation and the atmosphere is reasonably efficient in the top two-thirds of the forest, whereas the understorey remains partially isolated. At night, however, the canopy exhibits a significant decoupling from the overlying atmospheric layer due to substantial radiative cooling, causing a stable density stratification above. It is fairly clear that these variations in microclimate produce a spectrum of different living conditions for the flora and fauna.In addition, the collected data provide important information concerning the turbulent exchanges of heat and water vapour. Actual evapotranspiration loss from the forest was estimated using a single-layer version of the Penman-Monteith equation including a submodel of canopy conductance. The values computed for hourly and daily periods were found to agree well with the simultaneously recorded xylem sap flow of several tree species. Thus they prove that this application is suitable to describe the environmental impact of micrometeorological and physiological factors on the complex process of evapotranspiration.