Evaluation of various heat-pulse methods for estimation of sap flow in orchard trees: comparison with micrometeorological estimates of evaporation

Abstract

Summary.A microcomputer-controlled heat-pulse system for the measurement of sap velocity in trees is described. Several published methods for determining sap velocity from the temperature rise measured either above or below a heater inserted into the stem were compared and evaluated. All methods could be improved by the use of curve-fitting procedures, with a particularly useful approach involving direct estimation of the parameters of the diffusion equation using the non-linear curve-fitting package maximum likelihood programme. An alternative approach that was based on measurement of the value of the maximum temperature was proposed and tested. This was found to be particularly robust and sensitive to changes in flow rate. Although sap-flow velocity varied markedly with depth in the stem (as shown by the rate of dye movement), the maximum temperature at any given flow rate was found to be relatively insensitive to sensor depth. Estimated sap-flow velocities were compared with evaporation rates estimated either by weighing (for potted trees) or by the Penman-Monteith equation. Several independent methods were used for estimating the values of boundary layer resistance and net radiation that were required for application of the Penman-Monteith equation. There was a close relationship between flow and evaporation with some evidence for hysteresis. Although absolute calibration of the sap-flow estimates is difficult, the methods described are all useful for relative studies and all responded rapidly to altered flow rates caused by changing weather conditions. Offprint requests to: H. G. Jones

Sap flow measurements with some thermodynamic methods, flow integration within trees and scaling up from sample trees to entire forest stands

“…(5) Heat field deformation (HFD; . Detailed reviews of the above methods have been presented by Marshall (1958), Jones et al (1988), Campbell (1991), Cohen (1993), Swanson (1994), Čermák (1995), Granier (1995), Edwards et al (1996), Smith and Allen (1996), Braun (1997), Čermák and Nadezhdina (1998a,b,c), Gonzales-Altozano et al (1998), Kostner et al (1998), Wullschleger et al (1998) and others. Theoretical analysis indicating goals and drawbacks of different methods and showing possible ways for their improvement have been presented by Marshall (1958), Pickard and Puccia (1972), Pickard (1973), Swanson and Whitfield (1981), Swanson (1983), Valancogne and Nasr (1989), Groot and King (1992), Barret et al (1995), Grime et al (1995a) and Nadezhdina (1998).…”

“…Ranges of damaged elements at distances 3-20 cm in axial direction and up to distances comparable to probe diameter in tangential direction have been reported. In order to avoid HPV measurement errors, corresponding correction factors for different species have been empirically derived (Swanson 1971;Swanson and Whitfield 1981;Green and Nicholson 1987;Jones et al 1988;Green and Clothier 1988;Olbrich 1991). Similar situation also fits to HD and HFD needle-like sensors, whose diameter should be kept as small as possible.…”

How Reliable Are Heat Pulse Velocity Methods for Estimating Tree Transpiration?

“…Four of the seven theoretical methods have been extensively tested and include the compensation heat pulse method (CHPM, [10]), heat ratio method (HRM, [11,12]), T-max method [13], and Sapflow+ method [14]. The methods have been reviewed extensively elsewhere [9,12,[15][16][17][18]. Briefly, following a heat pulse, the CHPM measures the time for temperatures to be equal in sensors installed upstream and downstream to the heater probe.…”

Transpiration measurements on apple trees with an improved stem heat balance method

“…Fuchsine (0.5%) was added as a colour tracer ((~erm~ik et al, 1992;Jones et al, 1988). As a first step a staining experiment was carried out to get more detailed information about the spatial distribution of the sap flow within the xylem.…”