Wind speed and turbulence were measured at five heights simultaneously in a Costa Rican forest with non—stalling, heated—thermocouple anemometers. A persistent daytime stable thermal stratification of the air beneath the top canopy decreased small—scale turbulence, which may increase boundary—layer resistance of leaf—to—air transport of water vapor and CO2. Three CO2 source layers (ground level, trunk space, and above the top canopy) and two CO2 sink layers (top canopy and bottom canopy) were found in this forest. Low nocturnal wind speed allowed CO2 from respiration to accumulate at night.