Circumferential and radial variations in xylem sap flux density in trunks of 13-year-old mango (Mangifera indica L.) trees were investigated with Granier sap flow sensor probes under limiting and non-limiting soil water conditions. Under non-limiting soil water conditions, circumferential variation was substantial, but there was no apparent relationship between sap flux density and aspect (i.e., the radial position of the sensor probes on the trunk relative to the compass). Hourly sap flux densities over 24 hours at different aspects were highly pair-wise correlated. The relationships between different aspects were constant during well-watered periods but highly variable under changing soil water conditions. Sap flux density showed marked radial variation within the trunk and a substantial flux was observed at the center of the trunk. For each selected aspect on each tree, changes in sap flux densities over time at different depths were closely correlated, so flux at a particular depth could be extrapolated as a multiple of flux from 0 to 2 cm beneath the cambium. However, depth profiles of sap flux density differed between trees and even between aspects within a tree, and also varied in an unpredictable manner as soil water conditions changed. Nevertheless, over a period of non-limiting soil water conditions, depth profiles remained relatively constant. Based on the depth profiles obtained during these periods, a method is described for calculating total sap flow in a mango tree from sap flux density at 0-2 cm beneath the cambium. Total daily sap flows obtained were consistent with water use estimated from soil water balance.

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-Granier's technique of measuring sap flux density using a continuous heating system was tested on young mango trees. On containerized trees, sap flow underestimated transpiration measured gravimetrically by less than 10 %. In a 4-year-old field-grown tree, there was only a 5 % difference between cumulative summed sap flow in the branches and sap flow in the trunk over a 24-h period. Positioning of the sap flux sensor on the trunk was found to be non-critical for sap flow measurement in trees of diameter of less than 10 cm. Granier's sap flux sensor was sensitive to both slow and abrupt changes in canopy transpiration induced by successive branch girdling, defoliation and excision. A comparison of sap flow in the branches and water uptake by the tree measured using the 'cut-tree method' showed that sap flow method underestimated the actual water uptake by less than 6 %.