Estimating stand water use of large mountain ash trees and validation of the sap flow measurement technique

Abstract

Mountain ash (Eucalyptus regnans F.J. Muell.) forest catchments exhibit a strong relationship between stand age and runoff, attributed inter alia to differences in tree water use. However, the tree water use component of the mountain ash forest water balance is poorly quantified. We have used the sap flow technique to obtain estimates of daily water use in large mountain ash trees. First, the sap flow technique was validated by means of an in situ cut tree experiment. Close agreement was obtained between the sap flow estimate of water use and the actual uptake of water by the tree from a reservoir. Second, we compared the variability in sap velocity between a symmetric and an asymmetric tree by using multiple sap flow loggers. In the symmetric tree, velocity was fairly uniform throughout the xylem during the day, indicating that accurate sap flow estimates can be obtained with a minimal number of sampling points. However, large variations in sap velocity were observed in the asymmetric tree, indicating that much larger sampling sizes are required in asymmetric stems for an accurate determination of mean sap velocity. Finally, we compared two procedures for scaling individual tree sap flow estimates to the stand level based on stem diameter and leaf area index measurements. The first procedure was based on a regression between stem diameter and tree water use, developed on a small sample of trees and applied to a stand-level census of stem diameter values. Inputs to the second procedure were tree water use and leaf area of a single tree and the leaf area index of the stand. The two procedures yielded similar results; however, the first procedure was more robust but it required more sampling effort than the second procedure.

Water Use of Tree Lines: Importance of Leaf Area and Micrometeorology in Sub-Humid Kenya

“…Large radiation ranges were mainly found when daily fluctuations were measured. The diurnal variation in our sap-flow measurements closely followed radiation, similar to patterns found by Dye and Olbrich (1993), Smith et al (1997) and Vertessy et al (1997). However, daily radiation sums showed a narrower range.…”

Relating Water Use to Tree Vitality of Populus euphratica Oliv. in the Lower Tarim River, NW China

“…Estimation of the sapwood area of a tree stand is commonly achieved based on the correlation between growth parameters of the tree (e.g., diameter at breast height, crown size, biomass, leaf area index) and the sapwood area. Hatton and Vertessy's study showed that the area of xylem conducting tissue, DBH, and tree basal area were efficient upscaling parameters [42,43]. However, there are differences of sapwood width and sapwood area among different tree species, even among different individuals of the same tree species, which is influenced by the tree growth status [44,45], site condition [46,47], and tree genetic traits [48,49].…”

Multiscale remote-sensing retrieval in the evapotranspiration of Haloxylon ammodendron in the Gurbantunggut desert, China

“…The vegetation transpiration was calculated using the cross-sectional area method (Vertessy et al 1995(Vertessy et al , 1997:…”

“…At the plant scale, various measurement methods, including weighing lysimeters, ventilated chambers, radioisotopes, stable isotopes and heat balance/heat dissipation methods have been proven to be valuable tools for conducting basic and applied research (Wullschleger et al 1998). Sap flow instruments, the effective techniques to measure plant transpiration (Hatton et al 1995;Vertessy et al 1997), have been used to study the transpiration of Haloxylon ammodendron and Tamarix ramosissima in Taklimakan desert (Xu 2006;Xu et al 2008). At stand scale, the thermal pulse method has been effectively used to measure the stem sap flow of sub-deciduous (Wullschleger et al 2001;Zhang and Gong 2004;Zhang et al 2005).…”