© 2007 Heron Publishing—Victoria, Canada
A comparison of daily water use estimates derived from constant-heat sap-flow probe values and gravimetric measurements in
pot-grown saplings
Katherine A. McCulloh (1, 2, 3), Klaus Winter (4), Frederick C. Meinzer (5), Milton Garcia (4), Jorge Aranda (4) and Barbara Lachenbruch (1)
1. Department of Wood Science and Engineering, Oregon State University, Corvallis, OR 97331, USA / 2. Department of Forest Science, Oregon State University, Corvallis, OR 97331, USA / 3. Corresponding author (kate.mcculloh@oregonstate.edu) / 4. Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Republic of Panama / 5. USDA Forest Service, Forestry Sciences Laboratory, 3200 SW Jefferson Way, Corvallis, OR 97331, USA / Received September 18, 2006; accepted January 24, 2007; published online June 1, 2007
Summary
Use of Granier-style heat dissipation sensors to measure sap flow is common in plant physiology, ecology and hydrology. There
has been concern that any change to the original Granier design invalidates the empirical relationship between sap flux density
and the temperature difference between the probes. Here, we compared daily water use estimates from gravimetric measurements
with values from variable length heat dissipation sensors, which are a relatively new design. Values recorded during a one-week
period were compared for three large pot-grown saplings of each of the tropical trees Pseudobombax septenatum (Jacq.) Dugand and Calophyllum longifolium Willd. For five of the six individuals, P values from paired t-tests comparing the two methods ranged from 0.12 to 0.43 and differences in estimates of total daily water use over the week
of the experiment averaged < 3%. In one P. septenatum sapling, the sap flow sensors underestimated water use relative to the gravimetric measurements. This discrepancy could have
been associated with naturally occurring gradients in temperature that reduced the difference in temperature between the probes,
which would have caused the sensor method to underestimate water use. Our results indicate that substitution of variable length
heat dissipation probes for probes of the original Granier design did not invalidate the empirical relationship determined
by Granier between sap flux density and the temperature difference between probes.
Keywords:
Calophyllum longifolium, Granier sensors, Pseudobombax septenatum, variable length probes, validation.
