CARBON-CYCLE DYNAMICS AND SOIL RESPIRATION OF FORESTS UNDER NATURAL DEGRADATION IN THE GRAN-SABANA

The Gran Sabana in Southeastern Venezuela represents a big part of the venezuelan part of the Guayana highlands. The soils of the region, ma inly Oxisols, originate from sandstones and are deeply weathered. The content of nutrients (esp. Ca) typically is very low, pH is around 4.5 , Al saturation is extremely high (80-90%) and the CEC is very limited (2 mval/100g clay). Our investigation plots are situated on a ridge 1 180m asl. The annual precipitation during the investigation period rea ched 220mm. The dry period lasts three months (Jan. - Mar). Litterfall occurred throughout the year (5.2-7.6 Mg ha-1 yr-1) and followed a mo derate seasonal pattern. Soil respiration (8.9-12.2 Mg C ha-1 yr-1) sh owed a more pronounced seasonal dependency, in which the moisture cont ent of the organic layer and topsoil were the most important regulatin g factors. Fine root production was 7.4-11.4 Mg ha-1 yr-1 determined i n four sampling periods during 14 months. On the basis of the data pre sented, as well as biomass estimations of Dezzeo (1990), we reach a pr eliminary estimate of carbon stock and fluxes between the above - and belowground compartments, including an evaluation of the degradation p rocesses.