期刊
TREE PHYSIOLOGY
卷 33, 期 5, 页码 550-558出版社
OXFORD UNIV PRESS
DOI: 10.1093/treephys/tpt029
关键词
sap flux; sapwood area; scaling; thermal dissipation probe; water availability
类别
资金
- Ministry of Agriculture, Forestry and Fisheries, Japan
- Japan Society for the Promotion of Science [20.7279]
- CREST project from the Japanese Ministry of Education, Culture, Sports, Science and Technology
- Faculty of Agriculture, Kyushu University
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.
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