Carbon dioxide recycling in two Amazonian tropical forests

Recycling of respiratory CO2 was calculated with a previously developed model using stable isotope ratios and concentration values of ambient CO2. Measurements were taken at two different tropical forests in the Amazon basin during the dry season. One forest (Reserva Ducke) was characterized by a closed canopy with lower wind speeds, while the other (Fazenda Vitoria) had a relatively open canopy and higher wind speeds. The closed canopy forest had up to 39% of its respiratory CO2 recycled at 18 m above the forest floor. Percent recycling in this forest was related to wind speed at the date of collection. Calculations of recycling on the open canopy forest gave values ranging from 0 to negative. This forest may have ambient CO2 contamination from charcoal kilns in a nearby town. Thus, calculations of recycling based on isotopic composition of ambient CO2 for this forest may be incorrect. (C) 1997 Elsevier Science B.V.