CARBON-DIOXIDE EXCHANGE AND NOCTURNAL PROCESSES OVER A MIXED DECIDUOUS FOREST

This paper reports the results of the analysis of CO2 exchange from a one-month experiment conducted at a mixed deciduous forest, Camp Borde n (80 degrees 65'W, 44 degrees 19'N), Canada, in the summer of 1993. T he mid-day CO2 flux from the forest under clear sky conditions was aro und -1.0 mg m(-2) s(-1), the average light and water use efficiencies 13 mmol CO3(mol photon)(-1) and 7.95 mg CO2(g H2O)(-1), and the averag e nocturnal respiration rate 0.21 mg CO2 m(-2) s(-1). We observed diff erent flow features at heights of 34.5 (14.5 m above the canopy) and 2 2.4 m at night. Wavelike structures were frequently encountered at z = 34.5 m. Depending on the phase angle between the vertical velocity an d CO2 concentration time series, they could act to enhance the co-grad ient (upward) flux or to create counter-gradient (downward) flux of CO 2. We speculate that the wave events were limited to isolated regions in the upwind direction. Near the tree-tops (z = 22.4 m), the strong w ind shear was able to maintain turbulence. Inverse temperature ramp st ructures were very common and flux of sensible heat was well behaved ( directed downward).