A GEOGRAPHICALLY-BASED ECOSYSTEM MODEL AND ITS APPLICATION TO THE CARBON BALANCE OF THE LUQUILLO FOREST, PUERTO-RICO

We have developed a geography-based computer model of the Bisley Experimental Watershed ecosystem that simulates basic forest dynamics as a function of meteorological inputs and hydrologic simulation, as influenced by topography, soils, land use, and cover. The model is parameterized based on steady state levels of, and hurricane impacts on, biomass, necromass and rate processes of the tabonuco forest, and is stable over decades. Over a 60 yr simulation (without hurricanes) leaf biomass remains approximately constant and woody biomass of those regions not having severe sunlight, moisture, or nutrient limitations increases slowly in agreement with observations. Necromass decreases slowly. Small quantities at C leave the ecosystem in stream water, especially during large rain events. When topographically-sensitive hurricane impacts are included, leaf and woody biomass are converted to necromass. In the model the recovery of the watersheds' hydrology, leaf and woody biomass, and necromass are consistent with field observations. We used this model to simulate the C dynamics of the forest over centuries using empirical values and found that this forest acted to pump C from the atmosphere to the ocean at a rate of about 90 kg ha-1 yr-1.