© 2001 Heron Publishing—Victoria, Canada
Medium-term sap flux monitoring in a Scots pine stand: analysis of the operability of the heat dissipation method for hydrological
purposes
Imma Oliveras (1) and Pilar Llorens (1)
1. Institut de Ciències de la Terra ‘Jaune Almera,’ CSIC, Solé i Sabarís, s/n, 08028 Barcelona, Spain / Received July 6, 2000
Summary
The operability of Granier-type heat dissipation sap flow meters for the medium-term monitoring of Scots pine transpiration
was tested. Three sensors that had been working for 3 years were duplicated by inserting new sensors in the same trees. The
new sensors operated simultaneously with the old sensors for 18 months. Analysis of the temporal patterns of thermal dissipation
of the sensors showed a slight, but significant decrease in all sensors, indicating the conservation of sapwood thermal properties.
Although there was a high correlation between sap flux densities registered by the old and new sensors, significant differences
in sap flux densities between the duplicated sensors were detected. Such differences could not be attributed to tissue injury
around the sensors or to loss of sensitivity of the old sensors, because two of the old sensors registered higher flux rates
than the new sensors. No instrumental error to explain the sap flux differences was found. Because the new sensors were installed
at some angular distance from the old sap flow meters to avoid thermal interferences, it was inferred that the observed sap
flux differences between duplicate sensors were the result of an azimuthal sap flow pattern.
Keywords:
azimuthal patterns, Granier sap flow method, Pinus sylvestris, sap flux density.
