Radial patterns of sap flow in woody stems of dominant and understory species: scaling errors associated with positioning of sensors

Abstract

We studied sap flow in dominant coniferous (Pinus sylvestris L.) and broadleaf (Populus canescens L.) species and in understory species (Prunus serotina Ehrh. and Rhododendron ponticum L.) by the heat field deformation (HFD) method. We attempted to identify possible errors arising during flow integration and scaling from single-point measurements to whole trees. Large systematic errors of -90 to 300% were found when it was assumed that sap flow was uniform over the sapwood depth. Therefore, we recommend that the radial sap flow pattern should be determined first using sensors with multiple measuring points along a stem radius followed by single-point measurements with sensors placed at a predetermined depth. Other significant errors occurred in the scaling procedure even when the sap flow radial pattern was known. These included errors associated with uncertainties in the positioning of sensors beneath the cambium (up to 15% per 1 mm error in estimated xylem depth), and differences in environmental conditions when the radial profile applied for integration was determined over the short term (up to 47% error). High temporal variation in the point-to-area correction factor along the xylem radius used for flow integration is also problematic. Compared with midday measurements, measurements of radial variation of sap flow in the morning and evening of sunny days minimized the influence of temporal variations on the point-to-area correction factor, which was especially pronounced in trees with a highly asymmetric sap flow radial pattern because of differences in functioning of the sapwood xylem layers. Positioning a single-point sensor at a depth with maximum sap flow is advantageous because of the high sensitivity of maximum sap flow to water stress conditions and changes in micro-climate, and because of the lower random errors associated with the positioning of a single-point sensor along the xylem radius.

Survival and acclimatation ofPopulus nigrato drier conditions after damming of an alpine river, southeast France

“…It is more difficult to obtain figures for the water consumption of the whole tree because the sapwood of poplars can be quite thick [19]. Some authors have even given the relationship between the sapwood area (SWA) and the diameter at breast height (DBH) (cm) as: SWA = 6.39 × DBH 1.25 [28,35].…”

Species‐specific transpiration responses to intermediate disturbance in a northern hardwood forest

“…On this basis, we expected an overestimation of E C of roughly 11% in the control plot and 3.7% in the treatment plot. Due to the dependence of radial patterns in sap flow on species, tree age, and site history and, therefore, the large variability among reduction factors, we chose to disclose this limitation rather than to assume the applicability of a reduction factor from existing literature that was not specific to our plots [James et al, 2002;Nadezhdina et al, 2002;Phillips et al, 1996;Renninger et al, 2013;Schäfer et al, 2000;Shinohara et al, 2013]. Despite these errors, the roughly 15% difference in transpiration between the control and treatment plots remains significant.…”

Infra-red images of heat field around a linear heater and sap flow in stems of lime trees under natural and experimental conditions

“…Sensors consisted of a long linear heater and two pairs of thermocouples, of which one was placed symmetrically 1.5 cm up and down from the heater (measured symmetrical temperature difference dT sym ), while the other was placed asymmetrically at a short distance (1.0 cm) on one side of the heater (measured asymmetrical temperature difference dT as ) [21]. Reference ends of the thermocouples were at the same height below the heater.…”

“…1, middle panel). Position of the sensor in the stem is shown schematically below IR-image, observed at 15 21 . IR-image, marked by red frame, corresponds to 1 s after cutting.…”