Skip to Main Content
U.S. Forest Service
Caring for the land and serving people

United States Department of Agriculture

Home > Search > Publication Information

  1. Share via EmailShare on FacebookShare on LinkedInShare on Twitter
    Dislike this pubLike this pub


    Sap flow techniques, such as thermal dissipation, involve an empirically derived relationship between sap flux and the temperature differential between a heated thermocouple and a nearby reference thermocouple inserted into the sapwood. This relationship has been widely tested but mostly with newly installed sensors. Increasingly, sensors are used for extended periods. After several months, tree growth, wounding, or other changes in water flow path may impair sensor performance. To quantify changes in sensor performance over time, we installed 23 sensors (1 per tree) in 16-year-old Douglas-fir [Pseudotsuga mensiesii (Mirb.) Franco] and red alder (Alnus rubra Bong.) in the western Cascades of Oregon and measured daily average sap flux (Js) from April through July 200l and 2002. We assumed the measurements from 2001 to be unimpaired and the response of Js to vapor pressure deficit (ä) to be consistent under the same edaphic conditions. Differences from this assumption were attributed to "temporal sampling errors." During the study, soilmoisture (è), did not differ on similar calendar dates, yet the slope of Js versus ä decreased significantly in the second year. In 2002, Js in Douglas-fir was 45 percent less than in 2001; in red alder, 30 percent less. Variations in ä could not explain the differences. A correction for temporal sampling errors improved estimates of Js from sensors used for more than one season. Differences in temporal sampling errors between the two species reveal underlying causal mechanisms. Evidence is presented that cambial growth causes errors in Douglas-fir.

    Publication Notes

    • Visit PNW's Publication Request Page to request a hard copy of this publication.
    • We recommend that you also print this page and attach it to the printout of the article, to retain the full citation information.
    • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.


    Moore, G.W.; Bond, B.J.; Jones, J.A.; Meinzer, F.C. 2010. Thermal-dissipation sap flow sensors may not yield consistent sap-flux estimates over multiple years. Trees. 24: 165-174.


    Google Scholar


    Alnus rubra, Pseudotsuga menziesii, sap flux, sapwood, temporal sampling errors

    Related Search

    XML: View XML
Show More
Show Fewer
Jump to Top of Page