© 2004 Heron Publishing—Victoria, Canada
Time series diagnosis of tree hydraulic characteristics
Nathan G. Phillips (1, 2), Ram Oren (3), Julian Licata (4) and Sune Linder (5)
1. Boston University, Geography Department, 675 Commonwealth Avenue, Boston, MA 02215, USA / 2. Corresponding author (nathan@bu.edu) / 3. Duke University, Nicholas School of the Environment, Durham, NC 27708, USA / 4. Oregon State University, Forest Science Department, Corvallis, OR 97331, USA / 5. Swedish University of Agricultural Sciences, Southern Swedish Forest Research Center, SE-230 53 Alnarp, Sweden / Received June 24, 2003; accepted March 5, 2004; published online June 1, 2004
Summary
An in vivo method for diagnosing hydraulic characteristics of branches and whole trees is described. The method imposes short-lived
perturbations of transpiration and traces the propagation of the hydraulic response through trees. The water uptake response
contains the integrated signature of hydraulic resistance and capacitance within trees. The method produces large signal to
noise ratios for analysis, but does not cause damage or destruction to tree stems or branches. Based on results with two conifer
tree species, we show that the method allows for the simple parameterization of bulk hydraulic resistance and capacitance
of trees. Bulk tree parameterization of resistance and capacitance predicted the overall diel shape of water uptake, but did
not predict the overshoot water uptake response in trees to shorter-term variations in transpiration, created by step changes
in transpiration rate. Stomatal dynamics likely complicated the use of simple resistance–capacitance models of tree water
transport on these short time scales. The results provide insight into dominant hydraulic and physiological factors controlling
tree water flux on varying time scales, and allow for the practical assessment of necessary tree hydraulic model complexity
in relation to the time step of soil- vegetation-atmosphere transport models.
Keywords:
hydraulic capacitance, hydraulic resistance, sap flux, transpiration, xylem.
