PARENT SESSION
Oral Session #54: Vegetation: Controls on NPP, Global Climate Change. Presiding: W. Oechel.
Wednesday, August 8, 2001. 1:00 PM to 5:00 PM. Hall of Ideas G.
Seasonal and inter-annual variation in canopy foliage area of tropical rain forest in Costa Rica under ENSO and La Niña climate regimes.
Oberbauer, Steven 1, O'Brien, Joseph1, Clark, Deborah2, Clark, David 2, 1 2
ABSTRACT- Despite the importance of leaf area index (LAI) for ecosystem processes, little information is available on the LAI of tropical forests because adequate sample harvests of primary forests have not been conducted. Also lacking is information on seasonal and inter-annual variation of LAI. Relative changes in leaf area can be estimated with indirect methods that use canopy light interception. We used hemispherical photography to evaluate seasonal and inter-annual variation in canopy coverage at the La Selva Biological Station in Costa Rica during the years 1998-2000, which include mega ENSO (1998) and La Niña (1999) climate regimes. Canopy photographs were repeatedly taken over six random grid points within 18 study plots (0.5 ha) randomly stratified for soil and topographic type during dry season (March-April) and wet season (June-July). Estimated LAI was slightly greater on inceptisols than on ultisols (3.8 vs 3.6). We found large differences between wet and dry season canopy coverage during 1998 and 1999 (19 and 24%), but not in 2000 (1%), when the dry season was unusually wet. Overall, canopy coverage was very similar during 1999 and 2000, but both years differed from 1998, when many tree falls occurred during downdrafts.
KEY WORDS: drought, rainforest, soil moisture