Document Detail

An alternative method to estimate zero flow temperature differences for Granier's thermal dissipation technique.
MedLine Citation:
PMID:  17472936     Owner:  NLM     Status:  MEDLINE    
Calibration of the Granier thermal dissipation technique for measuring stem sap flow in trees requires determination of the temperature difference (DeltaT) between a heated and an unheated probe when sap flow is zero (DeltaT(max)). Classically, DeltaT(max) has been estimated from the maximum predawn DeltaT, assuming that sap flow is negligible at nighttime. However, because sap flow may continue during the night, the maximum predawn DeltaT value may underestimate the true DeltaT(max). No alternative method has yet been proposed to estimate DeltaT(max) when sap flow is non-zero at night. A sensitivity analysis is presented showing that errors in DeltaT(max) may amplify through sap flux density computations in Granier's approach, such that small amounts of undetected nighttime sap flow may lead to large diurnal sap flux density errors, hence the need for a correct estimate of DeltaT(max). By rearranging Granier's original formula, an optimization method to compute DeltaT(max) from simultaneous measurements of diurnal DeltaT and micrometeorological variables, without assuming that sap flow is negligible at night, is presented. Some illustrative examples are shown for sap flow measurements carried out on individuals of Erica arborea L., which has needle-like leaves, and Myrica faya Ait., a broadleaf species. We show that, although DeltaT(max) values obtained by the proposed method may be similar in some instances to the DeltaT(max) predicted at night, in general the values differ. The procedure presented has the potential of being applied not only to Granier's method, but to other heat-based sap flow systems that require a zero flow calibration, such as the Cermák et al. (1973) heat balance method and the T-max heat pulse system of Green et al. (2003).
Carlos M Regalado; Axel Ritter
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Validation Studies    
Journal Detail:
Title:  Tree physiology     Volume:  27     ISSN:  0829-318X     ISO Abbreviation:  Tree Physiol.     Publication Date:  2007 Aug 
Date Detail:
Created Date:  2007-05-02     Completed Date:  2007-11-29     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  100955338     Medline TA:  Tree Physiol     Country:  Canada    
Other Details:
Languages:  eng     Pagination:  1093-102     Citation Subset:  IM    
Dept. Suelos y Riegos, Instituto Canario de Investigaciones Agrarias, Apdo. 60 La Laguna, 38200 S/C Tenerife, Spain.
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MeSH Terms
Ericaceae / physiology*
Models, Biological*
Myrica / physiology*
Trees / physiology*

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