Sapwood and intermediate wood thickness variation in Japanese cedar: impacts on sapwood area estimates

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Variation in sapwood thickness (<i>T</i><sub>S</sub>) around the circumference of a stem and the presence of intermediate wood can cause errors in the estimation of sapwood area (<i>A</i><sub>S</sub>) and individual tree-scale transpiration (<i>Q</i>) based on the sap flow technique. We measured bark thickness (<i>T</i><sub>B</sub>), <i>T</i><sub>S</sub>, and intermediate wood thickness (<i>T</i><sub>I</sub>) in 16 orthogonal directions for wood discs from 57 Japanese cedar (<i>Cryptomeria japonica</i>) trees, and evaluated the impact of variation in <i>T</i><sub>S</sub> around the circumference of a stem and the validity of assuming a constant <i>T</i><sub>I</sub> for <i>A</i><sub>S</sub> estimates. The coefficient of variation of <i>T</i><sub>S</sub> in the 16 directions was 5.3–36.7%. <i>A</i><sub>S</sub> based on four orthogonal directions resulted in only minor errors for all trees, although this was not the case for <i>A</i><sub>S</sub> based on one and two directions. The mean <i>T</i><sub>I</sub> over the 16 directions was not significantly correlated to the diameter. If <i>T</i><sub>I</sub> was assumed to be constant at the median value for our forest (=0.8 cm), the relative absolute errors for six of the 57 trees exceeded 30%. If these errors are unacceptable, we recommend extracting stem discs to measure <i>T</i><sub>I</sub> when estimating <i>A</i><sub>S</sub> and <i>Q</i> for trees with intermediate wood having a similar color to sapwood.


  • Hydrological Research Letters

    Hydrological Research Letters 9(2), 35-40, 2015

    Japan Society of Hydrology and Water Resources (JSHWR) / Japanese Association of Groundwater Hydrology (JAGH) / Japanese Association of Hydrological Sciences (JAHS) / Japanese Society of Physical Hydrology (JSPH)


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