Effect of irrigation on sap flux density variability and water use estimate in cherry (Prunus avium) for timber production: Azimuthal profile, radial profile and sapwood estimation

Abstract

Information on tree water use in plantations for high quality wood is scarce, thus studies are needed toproperly estimate the irrigation demand of these plantations. Plant water use estimation with sap flowsensors has been used extensively. However, biases in tree sap flow estimate can arise from variationson radial and azimuthal profiles of sap flux density and also from the sapwood area considered for theup-scaling from sap flux density to sap flux. This work aimed to (1) study the spatial variations of sapflux density in cherry trees in a timber orientated plantation, (2) compare several methods to estimatesapwood depth in cherry trees and (3) to evaluate the effect of drip irrigation on these factors. The resultsshowed that most of the studied trees had decreasing radial sap flux density profiles with depth asexpected. However, the three irrigated trees of bigger sizes still showed high sap flux densities in theirinner tissues, at contrast with the rest of the trees and especially with the non irrigated ones of similarsize with values close to 20% of the sap flux density measured at 1 cm depth from cambium. On the otherhand, the different methods tested to estimate sapwood depth gave significantly different results andonly the two methods of visual identification in wood cores based on color change and measurementsof sap flux densities along the xylem radius may be considered suitable for scaling purposes. Moreover,azimuthal variation pattern was found to be random in all the studied trees, and the ranking between theaspects (north, south, east and west) was not affected by either drip irrigation or sun exposition, and thusmeasuring sap flux density in any particular aspect has been shown to be suitable to estimate the overalltree sap flux. We conclude that more studies are necessary to properly assess the radial profile of sapflux density, especially when considering the high sap flux density in the inner tissues of the three biggerirrigated trees as compared to the other trees, and also how this pattern seemed to indicate sapwooddepths values very contrasted to the ones estimated from color change in wood cores.