© 2001 Heron Publishing—Victoria, Canada
Regulation of water flux through tropical forest canopy trees: Do universal rules apply?
F. C. Meinzer (1, 3), G. Goldstein (2) and J. L. Andrade (1, 4)
1. Hawaii Agriculture Research Center, 99-193 Aiea Heights Drive, Suite 300, Aiea, HI 96701, USA / 2. Department of Botany, University of Hawaii, 3190 Maile Way, Honolulu, HI 96822, USA / 3. USDA Forest Service, Forestry Sciences Laboratory, 3200 SW Jefferson Way, Corvallis, OR 97331-4401, USA / 4. Centro de Investigación Científica de Yucatán, A.C. Apdo. Postal 87 Cordemex, 97310, Méida, Yucatán, México / Received April 19, 1999
Summary
Tropical moist forests are notable for their richness in tree species. The presence of such a diverse tree flora presents
potential problems for scaling up estimates of water use from individual trees to entire stands and for drawing generalizations
about physiological regulation of water use in tropical trees. We measured sapwood area or sap flow, or both, in 27 co-occurring
canopy species in a Panamanian forest to determine the extent to which relationships between tree size, sapwood area and sap
flow were species-specific, or whether they were constrained by universal functional relationships between tree size, conducting
xylem area, and water use. For the 24 species in which active xylem area was estimated over a range of size classes, diameter
at breast height (DBH) accounted for 98% of the variation in sapwood area and 67% of the variation in sapwood depth when data
for all species were combined. The DBH alone also accounted for ≥ 90% of the variation in both maximum and total daily sap
flux density in the outermost 2 cm of sapwood for all species taken together. Maximum sap flux density measured near the base
of the tree occurred at about 1400 h in the largest trees and 1130 h in the smallest trees studied, and DBH accounted for
93% of the variation in the time of day at which maximum sap flow occurred. The shared relationship between tree size and
time of maximum sap flow at the base of the tree suggests that a common relationship between diurnal stem water storage capacity
and tree size existed. These results are consistent with a recent hypothesis that allometric scaling of plant vascular systems,
and therefore water use, is universal.
Keywords:
allometric relationships, sap flow, sapwood, stem water storage.
