© 1989 Heron Publishing—Victoria, Canada
Comparative analysis of photosynthetic light environments within the crowns of juvenile rain forest trees
S. F. Oberbauer (1), D. A. Clark (2), D. B. Clark (2) and M. Quesada (3)
1. Department of Biological Sciences, Florida International University, Miami, FL 33199, and Fairchild Tropical Garden, 11935
Old Cutler Road, Miami, FL 33156, USA / 2. Organization for Tropical Studies, Apartado 676, 2050 San Pedro, Costa Rica / 3. Department of Biology, Pennsylvania State University, University Park, PA 16802, USA / Received August 19, 1988
Summary
Irradiances within the crowns of saplings of two tropical tree species were simultaneously compared in primary rain forest
in Costa Rica. The species examined, Minquartia guianensis Aubl., a relatively slow-growing, canopy species, and Pithecellobium pedicellare (DC) Benth., a less-tolerant, emergent species, have different crown and leaf display patterns. Crown light environments
were assessed by placing arrays of quantum sensors among leaves and recording at 5-s intervals for seven days with microloggers.
Median total daily quantum flux densities for saplings of both species were less than 2% of full sun and did not differ significantly.
More than 90% of the measurements within the crowns of these saplings were less than 25 μmol m–2 s–1. Spatial variability of photon flux densities within sapling crowns was similar for the two species despite differences in
leaf display patterns. In saplings of both species, photon flux densities varied significantly over the relatively short distances
within crowns and from day to day. Height growth of both species was significantly correlated with total daily photon flux
densities and with percentage of full sun. However, only the tolerant species, Minquartia, showed a significant correlation
between diameter growth and crown light environment.
