The heat pulse velocity technique for determining water uptake of Populus deltoides

Abstract

The heat pulse velocity (HPV) technique was selected as a possible effective means of determining water uptake, and thus transpiration, of Populus deltoides trees growing in the riparian zones. The method is based on the measurement of sap flow through the tree stem. Prior to field determinations of sap flow, the technique required verification for the species against a direct measure of water uptake, provided in this study by the cut-tree method. The HPV apparatus was also used to investigate the relation between the radial heat pulse velocity profile and the position of annual growth rings, which could affect the placement of HPV probes in the tree. The HPV method accurately estimated sap velocity for two 10-year-old Populus deltoides trees in a riparian zone near Franschoek in the western Cape Province, providing single-day estimates differing 10.2% and 4.7%, respectively, from the cut-tree method. The parabolic heat pulse velocity profile was unaffected by the presence of narrow growth rings. Die hitte-pols-snelheid-tegniek (HPS tegniek) is uitgekies as ’n moontlike effektiewe manier om water-opname, en dus ook transpirasie, van Populus deltoides bome wat in oewergebiede groei, te bepaal. Die metode is gebaseer op die meet van vogvloei deur die stam van die boom. Voor veldbepalings van vogvloei gedoen kon word, het die tegniek verifikasie vir die spesie vereis deur ’n direkte bepaling van wateropname, wat in hierdie studie deur die afgesnyde-boom-tegniekverskaf word. Die HPS apparaat is ook gebruik om die verhouding tussen die radiale hitte-pols-snelheid-profielen die posisie van die jaarringe te ondersoek, wat die plasing van die HPS peilstiwwe in die boom kan beïnvloed. Die HPS apparaat het die vogvloei van twee 10-jaar-oue Populus deltoides borne in die oewergebied naby Franschoek in die Wes-Kaap akkuraat beraam, en het enkeldagberamings wat respektiewelik 10.2% en 4.7% van die afgesnyde-boom-tegniek verskil het, verskaf. Die paraboliese hitte-pols-snelheid-profiel is nie deur die teenwoordigheid van smal jaarringe beïnvloed nie.