Using heat pulse and deuterium tracing techniques to estimate tree water use

In order to assess the effect that trees have on the water balance it is necessary to obtain quantitative knowledge regarding tree water use. This study compared the use of heat pulse and deuterium tracing techniques for estimating sap flux in a stand of 5 year old Eucalyptus grandis trees in south east Queensland, Australia. Comparisons of sap flux from 10 trees, representing the range of tree sizes in the stand, identified some substantial differences between the methods at the scale of the individual tree (between 12 % and 43 %). Using tree diameter as a scaling parameter, water use of the stand was also calculated, and a variety of scaling scenarios investigated. This included the potential of combining the heat pulse and deuterium tracing techniques in order to increase sample size, and hence confidence in scaling estimates. Despite differences at the scale of the individual tree, this study has shown there is potential to combine the two methods and still maintain an adequate level of precision.