A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

LITTER DYNAMICS IN AN UPLAND FOREST TOPOSEQUENCE IN CENTRALAMAZONIAMaria Terezinha F. Monteiro & Flavio J. Luizao. INPA-Ecology.E-mail: mtfmonteiro@aol.comFine litter production, its nutrient contents, and litter-layer deposition andchanges over time were studied in a toposequence of an upland moist forest incentral Amazonia, 80 km north of Manaus. The aim of this study was to assess thedynamics of litter production and deposition at different climatic periods of the year(dry and wet season) and topographic positions in the local relief. Three plots wereestablished in each of three distinct topographic levels: plateau, slope and valley,at km 34 of the secondary road ZF-2. Litterfall was measured semi-monthly in tensquared 50 cm X 50 cm traps for each plot. Litter was sorted into four maincomponents: leaves, woody material, reproductive structures, and fine fractions.Macronutrients (N, P, K, Ca, Mg) were analysed on oven-dried leaf samples. Leafcarbon concentration was determined by elemental CHN Analyser. Each 3 months,samples of the litter layer were also taken, in the same plots used for measuringlitter production, in order to follow the dynamics of litter deposition on forest floor.The greatest litter production, during the dry period, occurred in the plateau (1.17 tha -1 ), while the smallest one was measured in the valley plots (0.67 t ha -1 ). Thesame patttern was found in the wet season (0.48 t ha -1 in the plateau and 0.41 t ha -1 in the valley), when much less litter was produced in all topographic positions.However, higher proportion of leaves (81%) were recorded at the plots located inthe slopes, while more woody material (17%) was found in the valley plots. Thegreatest C/N ratio was found in the valley (43.7), while lower ratios were recordedin the slope (33.9), suggesting that faster litter decomposition and more efficientnutrient recycling occurs in the slopes. During the dry season, higher leaf Cconcentrations were found in the slope samples. There are indications of higherefficiency of C fixation at the slope, which agrees with other current work made inthe same forest location.