Comparison of Trunk and Branch Sap Flow with Canopy Transpiration in Pecan

Abstract

Trunk and branch sap flow were compared with canopy transpiration in a 5-year-old pecan tree (Carya illinoensis ‘Wichita’). Total trunk sap flow, measured by a heat balance trunk flow gauge, was 122.8 kg over a 24 h period, corresponding closely to the 113.4 kg of canopy transpiration measured by a large precision weighing lysimeter. Branches, less than half the diameter of the main trunk, had a total sap flow an order of magnitude less than the total flow in the trunk. Sap flow in a branch with a northern exposure was 41% less than that with a southern exposure. When sap flow was normalized per unit tree or branch leaf area, peak sap flow in the south branch matched that in the main trunk. Tree transpiration and the sap flow in trunk and branches began concurrently, indicating little dynamic water storage in the trunk above the gauge. The hydraulic conductance of the entire tree was 8 to 14 × 10−14 m s−1 Pa−1, similar to values found for a number of woody and herbaceous species.