Document: DAV-3-63-12

Heterogeneity in tropical rain forest structure and dynamics across a terra firme nutrient and topographic gradient.

CLARK, D.B.* ¹, D.A.CLARK ¹, S.F.OBERBAUER ² and E.VELDKAMP ³

University of Missouri-St. Louis, St. Louis, MO 63121, U.S.A. ¹
Florida International University, Miami, FL 33199, U.S.A. ²
University of Goettingen, Goettingen, GERMANY ³

Abstract:
Understanding tropical forests at landscape scales requires replicated sampling across ecologically important gradients. We used a stratified random block design to site 18 0.5 ha plots in old-growth tropical rain forest (TRF) in Costa Rica in three contrasting conditions: Flat relatively fertile sites (Inceptisols), flat infertile sites (Ultisols), and steeply sloping infertile sites (Ultisols). Number of stems >10 cm diameter was significantly higher in steep infertile plots (552/ha) than in the flat fertile sites (410/ha). Death rates over the period 1997-1999 varied an order of magnitude among plots, from 0.7 to 10.8%/yr. Contrary to our a priori hypotheses, plots on more fertile soils had the lowest death rates (2.3%/yr), and steeply sloping plots were intermediate in mortality (3.2%/yr); flat infertile plots averaged 5.0% mortality/yr. Patchy multi-tree blowdowns contributed to the substantial variance in death rate among plots. Overall, one-third of tree deaths were directly caused by another tree falling on them. The all-stems death rate was 3.6%/yr, one of the highest reported for an old-growth TRF. It is too early in this long-term study to identify the cause(s) for this high rate, but possible factors include El Nio events, long-term warming trends, or a demographic effect due to short measurement intervals. Overall these data show that there is substantial intra-landscape variance in the structure and dynamics of terra firme tropical forests, and that this variation is related to gradients in soil and topographic conditions.

Keywords: tropical rain forest; mesoscale landscapes; heterogeneity in structure and process; forest mortality rates; edaphic effects on forest structure and function

This abstract is being presented at: 11:30 AM in session:
Oral Session #42: Disturbance Ecology: Effects of Storms.