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- Title
Can we assume insignificant temporal changes in spatial variations of sap flux for year-round individual tree transpiration estimates? A case study on Cryptomeria japonica in central Taiwan.
- Authors
Tseng, Han; Chiu, Chen-Wei; Laplace, Sophie; Kume, Tomonori
- Abstract
Key message: Although spatial variations in sap flux changed seasonally in cedar trees, neglecting these seasonal changes generally resulted in less than 10% errors in year-round tree transpiration estimates. Abstract: Spatial and temporal variations in sap flux ( F ) affect the accuracy of year-round individual tree water use ( Q) estimates. We aimed to determine seasonal changes in radial and azimuthal variations in F and to evaluate their potential impacts on year-round Q estimates for humid subtropical forest trees. We measured F using 38 probes in eight Cryptomeria japonica trees in Taiwan from July 2010 to May 2011. During the study period, the ratio of inner F to outermost F ( R ) ranged between 0.29 and 0.68. The ratio of mean outermost F to that at one direction ( R ) ranged between 0.36 and 1.89. The seasonal patterns were inconsistent among individuals. We compared year-round Q estimates derived from multi-sensor measurements ( Q ) with those derived from measurements at a certain position with constant correction factors for radial ( Q ) or azimuthal ( Q ) patterns of F determined from the summer measurements. This simple exercise revealed consistent relationships between Q and Q year-round (<10% error), suggesting that seasonal changes in the radial profiles of F had little effect on Q estimates. Although using a constant correction factor for azimuthal variations led to 20-40% errors in Q of some individuals with large azimuthal variations (i.e., CV > 0.49), five out of eight individuals had less than 10% errors in their Q estimates. These results suggested that constant correction factors can be used for radial variations in year-round Q estimates, but are not applicable for azimuthal variations in individuals showing large azimuthal variations of F .
- Subjects
TAIWAN; SAP (Plant); PLANT transpiration; CRYPTOMERIA japonica; SPATIAL variation; CEDAR
- Publication
Trees: Structure & Function, 2017, Vol 31, Issue 4, p1239
- ISSN
0931-1890
- Publication type
Article
- DOI
10.1007/s00468-017-1542-6