Using branch and basal trunk sap flow measurements to estimate whole-plant water capacitance: comment on Burgess and Dawson (2008)

Abstract

Sap flow sensors are uniquely able to continuously monitor whole tree physiology. Recently, Burgess and Dawson (Burgess SSO, Dawson TE, Plant Soil 305:5–13, 2008) urged caution in using sap flow probes to estimate water storage use in trees. Here we respond to three criticisms raised there: (1) Sampling: that tree water storage, estimated from branch-bole sap flow lags, was compromised by unaccounted variation in branch position and orientation; (2) Instrumentation: that sap flow sensor response times may be sensor artefacts rather than manifestations of tree water storage; and (3) Theory: that tree water storage estimates are based on a faulty concept of lag phenomena in sap flow that persists in the literature. We agree with the need for caution in sap flow-based estimates of plant water storage, but here correct flaws in arguments and representations of studies presented in Burgess and Dawson (Burgess SSO, Dawson TE, Plant Soil 305:5–13, 2008).