Publication Date:
2013-05-16
Description:
Understanding radial and azimuthal variation, and tree-to-tree variation, in sap flux density ( F d ) as sources of uncertainty is important for estimating transpiration using sap flow techniques. In a Japanese cedar ( Cryptomeria japonica D. Don.) forest, F d was measured at several depths and aspects for 18 trees, using heat dissipation (Granier-type) sensors. We observed considerable azimuthal variation in F d . The coefficient of variation (CV) calculated from F d at a depth of 0–20 mm ( F d1 ) and F d at a depth of 20–40 mm ( F d2 ) ranged from 6.7 to 37.6% (mean = 28.3%) and from 19.6 to 62.5% (mean = 34.6%) for the azimuthal directions. F d at the north aspect averaged for nine trees, for which azimuthal measurements were made, was obviously smaller than F d at the other three aspects (i.e., west, south and east) averaged for the nine trees. F d1 averaged for the nine trees was significantly larger than F d2 averaged for the nine trees. The error for stand-scale transpiration ( E ) estimates caused by ignoring the azimuthal variation was larger than that caused by ignoring the radial variation. The error caused by ignoring tree-to-tree variation was larger than that caused by ignoring both radial and azimuthal variations. Thus, tree-to-tree variation in F d would be more important than both radial and azimuthal variations in F d for E estimation. However, F d for each tree should not be measured at a consistent aspect but should be measured at various aspects to make accurate E estimates and to avoid a risk of error caused by the relationship of F d to aspect.
Print ISSN:
0829-318X
Electronic ISSN:
1758-4469
Topics:
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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