Document: JOS-3-32-18

Physiological response of tropical rainforest canopy trees to climate.

O'BRIEN, J.J.* and S.F.OBERBAUER

Florida International University, Miami, FL 33102 USA ¹

Abstract:
Understanding the effects of climate on the physiology of tropical rainforest trees is crucial to predicting the future carbon balance of these highly productive forests. In order to model tree ecophysiological responses and to measure their variability within and among species, we measured micrometeorological variables and tree transpiration rates in a Costa Rican old growth tropical rainforest. We estimated whole tree water use with xylem radial flow meters (Granier sensors) installed in 16 mature canopy trees and recorded sap flow over several months in 1999. The trees were between 50 to 70 cm in diameter and were approximately 20 to 30 meters tall. Simultaneous micrometeorological measurements were made at a weather station installed on a 30 meter high antenna nearby in the forest. We condensed the meteorological data using a principle components analysis, which had the added benefit of eliminating multicolinearity among the weather variables. The first four factors explained 42.6%, 14.8%, 11.5% and 10.1% of the variance respectively, for a total of 79%. The first factor loaded heavily on insolation, air temperature and wind speed. The second factor was most influenced by soil temperature and soil moisture, the third by rainfall and the fourth by wind direction. We used the four sets of factor scores as explanatory variables in a linear multiple regression of xylem sap flow rates. The first factor was most important in predicting sap flow in all cases, usually explaining 80 to 90 percent of the variance, except in one species where it explained only 50 to 60 percent. Regression coefficients varied more within individuals of a species than among species. This might be explained by idiosyncratic effects such as tree health, liana load or local site conditions. We plan to build a predictive model of tree responses to climate with the results of our regression analysis.

Keywords: sap flow, response functions, tropical rainforest

This abstract is being presented at: 9:15 AM in session:
Oral Session #43: Plant Community Responses to Climate Change.