PARENT SESSION
Oral Session # 50: Forest Ecology III: Modeling; Nutrient Cycling.
Presiding: L Comas
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 100.
Interannual variation in tropical rain forest carbon cycling: a long-term, intensive study (La Selva, Costa Rica).
Clark, Deborah*,1, Clark, David1, Oberbauer, Steven2, 1 University of Missouri-St. Louis, St. Louis, MO, USA2 Florida International University, Miami, FL, USA
ABSTRACT- The responses of tropical rain forests to on-going climate change have large implications for the rate of accumulation of atmospheric carbon dioxide. Because there have been few long-term studies of carbon cycling in these forests, there is limited understanding of how the net carbon balance of these ecosystems might respond to changing climate. In an on-going team effort (the CARBONO Project), researchers have been collaborating since 1996 to investigate the forest carbon cycle in old-growth tropical wet forest at La Selva. We synthesize here the major findings from the first five years of research in the CARBONO plots, a set of 18 0.5-ha plots that were sited using the La Selva GIS so as to sample the landscape's large edaphic gradients (slopes to alluvial terraces, 3-fold variation in soil P, K, Al) with an unbiased, replicated design. The on-going measurements of carbon stocks and fluxes in these plots began in September 1997. They include: fine litterfall (biweekly), fine woody litterfall (monthly), initial stocks and yearly inputs of coarse woody debris, aboveground biomass increment (yearly), soil respiration (biweekly), fine root stocks (3-4 times per year), tree dynamics and species composition (yearly), and canopy structure (annual gap-mapping). The first five years' data revealed substantial interannual variation in carbon cycling in this forest, principally with respect to CARBONO Year 1, which overlapped the 1997/8 mega-Niño event. In that record-hot year, estimated aboveground biomass increment was 39% lower than in the following cooler years. In Year 1 we also measured enhanced leaf litterfall (but reductions in the other fine litter components), a large spike in dead fine roots, greatly enhanced tree mortality (returning to baseline mortality rates by Year 4), and large inputs of coarse woody debris. Our findings demonstrate that carbon cycling in this forest responds strongly to current-time climatic variation.
Key words: tropical rain forest, climate change, carbon cycling, forest dynamics