© 1996 Heron Publishing—Victoria, Canada
Variation of sapflow velocity in Eucalyptus globulus with position in sapwood and use of a correction coefficient
Daoqun Zang (1), C. L. Beadle (2) and D. A. White (2)
1. Chinese Academy of Forestry, Beijing 100091, P.R. China / 2. CSIRO Division of Forestry and Cooperative Research Centre for Temperate Hardwood Forestry, Locked Bag No. 2, Sandy Bay, Tasmania
7005, Australia / Received March 6, 1995
Summary
Sapflow sensors were used to investigate variation in sapflow velocity at different positions in the sapwood of three-year-old
Eucalyptus globulus ssp. globulus Labill. trees. Sapflow velocity was measured at 5-mm intervals across the sapwood by moving two probe sets simultaneously
on two opposite radii. Another probe set placed in a fixed position at right angles to the first two sets acted as a control.
A sapflow velocity ratio was defined as the velocity given by each moving sensor divided by that given by the static sensor.
Correlation between observations of sapflow velocity at different positions exceeded 95%, and the ratio of velocity between
any pair of sensors was constant.
We observed radial variation in sapflow velocity across the sapwood with the lowest velocities at the center of the tree.
Variation due to sensor position was high implying the need for large numbers of sensors for accurate estimates of sap flux.
To overcome this need, we used a correction coefficient, namely a simple weighted average of the sapflow ratios with depth
in the sapwood, for each fixed sensor. We recommend the use of three probe sets to estimate the correction coefficient. Subsequently,
two probe sets can be placed at two fixed positions for routine measurements of sap flux.
Keywords:
heat pulse velocity, sapflow sensor, sap flux, transpiration, xylem.
