PARENT SESSION
Oral Session #15: Ecosystem Ecology. Presiding: J. Jenkins.
Monday, August 6, 2001. 1:00 PM to 4:45 PM. Hall of Ideas F.
Determinants of regional variability in litter production of forests in the Southern Yucatan: environmental gradients or human legacy?
Lawrence, Deborah1,2, Foster, David2, 1 2
ABSTRACT- The Southern Yucatan is the deforestation frontier for the largest block of dry tropical forest in Central America. Our goal was to assess how human disturbance alters patterns of productivity driven by natural gradients of precipitation and soil fertility. We sampled litter production and soils in three regions (rainfall 890-1420 mm yr-1). We studied 8-10 stands 2-25 yrs old plus 2-3 mature forest stands per region (36 in total). Litter was collected monthly from four 1-m2 traps within a 500-m2 area, and summed for 1999. Soil chemical and physical properties varied little across the region, but organic matter increased (10.9-13.3%, 0-15 cm) with annual precipitation. Annual litter production was analyzed as a function of region, forest age, number of previous cycles of shifting cultivation, and total number of years in corn production. Region had no significant effect on production, though there was a trend toward higher production in the wettest region. Litterfall increased with age, and production in old secondary forests was not significantly different from that in mature forests. Land-use intensity was negatively correlated with litter production, which declined as a function of both number of cycles and total number of years in corn. In stepwise regression models, age and number of years in corn were the only significant predictors of litter production. Human history, rather than environmental gradients, seems to determine regional variation in productivity in the Yucatan.
KEY WORDS: tropical, forest, litterfall, disturbance