Journal of Tropical Ecology



Survival and ecophysiology of tree seedlings during El Niño drought in a tropical moist forest in Panama


Bettina M. J. Engelbrecht  a1 a2 c1 , S. Joseph Wright  a2 and Diane De Steven  a3
a1 Department of Biology, University of Utah, Salt Lake City, UT 84112-0840, USA
a2 Smithsonian Tropical Research Institute, P.O. Box 2072, Balboa, Panama
a3 USDA Forest Service, Southern Research Station, Center for Forested Wetlands Research, 2730 Savannah Highway, Charleston, SC 29414 USA

Abstract

In tropical forests, severe droughts caused by El Niño events may strongly influence the water relations of tree seedlings and thereby increase their mortality. Data on known-aged seedlings of three common shade-tolerant canopy tree species (Trichilia tuberculata, Tetragastris panamensis and Quararibea asterolepis) in a Panamanian moist forest are presented. Seedling survival during a severe El Niño dry season (1997-98) was compared with prior long-term survival data, and levels of drought stress were assessed by measuring plant water potentials and gas exchange characteristics. Contrary to prediction, dry-season seedling survival was not dramatically reduced in any species compared with that expected in ‘normal’ years. In Trichilia and Quararibea, pre-dawn water potentials averaged −2 MPa and midday water potentials about −3 MPa. Stomatal conductances were very low, averaging 26 mmol m-2 s-1 for Tetragastris and 11–13 mmol m-2 s-1 for Trichilia and Quararibea. Photosynthetic rates also were very low but consistently positive, averaging 0.8–1.1 μmol m-2 s-1. The findings suggest that, once established, seedlings of common tree species in this semi-deciduous forest may be tolerant of drought events.

(Accepted August 15 2001)


Key Words: El Niño Southern Oscillation; tropical forest; Panama; Quararibea asterolepis; seedling survival; stomatal conductance; Tetragastris panamensis; Trichilia tuberculata; water relations.

Correspondence:
c1 Corresponding author. Present address: Smithsonian Tropical Research Institute, Apto. 2072, Balboa, Panama