TRANSPIRATION OF NATURAL RAIN-FOREST AND ITS DEPENDENCE ON CLIMATIC FACTORS

Sap flow was measured on several species from the tropical rain forest in French Guiana during two successive years over the dry season, On bright days, sap flow densities (i.e. sap flow per unit of sapwood are a) exhibited high variations from one species to another. Higher rates (3 to 4 kg dm(-2) h(-1)) were observed on late stage forest species l ike Dicorynia guianensis, Eperua falcata or E. grandifolia, and lower rates on Vouacapoua americana and Carapa procera (1.0 to 1.5 kg dm(-2) h(-1)). Calculated stand sap flow (F) was closely dependant on air va pour pressure deficit and less correlated to global radiation. A simpl e model of canopy conductance variations and hence of stand transpirat ion was derived from these measurements. Sap flow was linearly related to Penman Evapotranspiration (PET), the ratio F/PET being close to 0. 75 under dry canopy conditions, as previously reported by Shuttleworth et al. (1984) in Central Amazon.