Temporal patterns of water flux in trees and lianas in a Panamanian moist forest
Trees - Structure and Function
Using constant heat sap flow sensors, xylem water fluxes in ten tree species and two liana species were monitored for 5â€šÃ„Ã¬10 days during the beginning of the wet season in May, 1993. For a subset of the trees, a branch was also monitored at the top of the crown for 5 days. Xylem flux (J S) was related diurnally in all plants to vapor pressure deficit (D) measured within the upper-third of the canopy, and to incoming shortwave radiation R S above the canopy. Cross-correlation analysis was used to estimate time lags between diurnal patterns of J S and D or R S, and between J S in stems and branches. The maximum correlation coefficient from cross-correlation of J S with R S (range=0.57â€šÃ„Ã¬0.92) was often higher than the maximum of J S with D (range=0.43â€šÃ„Ã¬0.89), indicating that diurnal J S was more dependent on R S than D. Time lags (lag corresponding to maximum correlation) of J S at stem-base with D was shorter (0â€šÃ„Ã¬45 min) than with radiation (5â€šÃ„Ã¬115 min), highly variable within a species, and uncorrelated to the height or exposure of tree crowns or liana in the canopy. On a stand level, not accounting for the diel lag between stem sap flux and canopy flux resulted in errors in estimated canopy transpiration of up to 30%.