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

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