PARENT SESSION
Session #18: Mechanisms underlying the maintenance of diversity and mode of regeneration in tropical forests: tests of alternative hypotheses. Organized by: W.P. Carson, C. Gehring, and T. Theimer.
Wednesday, August 8, 2001. Madison Ballroom B
Tree growth variation across tropical rain forest landscapes and its contribution to tree species diversity.
Clark, David1, Clark, Matthew2, Clark, Deborah1, Mackensen, Jens3, Veldkamp, Edzo3, 1 2 3
ABSTRACT- Many tropical rain forest tree species are non-randomly distributed across mesoscale non-swamp landscapes. A variety of processes can lead to such distributions, including spatial heterogeneity in biotic and abiotic variables, local site history, and anthropogenic influences. Here we examine the impact of within-landscape variation in soil nutrients on species' growth rates for a lowland rain forest where nutrient variation has been characterized in unique detail. Soil samples were taken from 1170 points on a 50 x 100 m grid over 584 ha of old-growth forest. Substantial gradients in cations, total P, N, and C were found across upland areas, with total P ranging from 0.55 to 1.97 mg/g and effective CEC from 47 to 132 mmol(+)/kg. We used a GIS to assign a predicted nutrient status to microsites of >2500 trees from a 17-yr demographic study of 10 species with contrasting life histories. Similarly, we used performance over 3 yr of >4400 trees >10 cm diameter in 18 0.5 ha plots to assess nutrient/growth relationships for many additional species. Our findings address the following issues: how frequent is nutrient limitation of growth among species? if present, at what life history stage does nutrient limitation occur? do species-level growth responses show spatial patterns that parallel those of certain soil nutrients? The answers to these questions will be discussed in relation to maintenance of the landscape-scale distribution of tree species diversity.
KEY WORDS: tropical rain forest , tree species diversity , tropical soil nutrients , GIS applications