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Research Project: Understanding Ecological, Hydrological, and Erosion Processes in the Semiarid Southwest to Improve Watershed Management

Location: Southwest Watershed Research Center

Title: Thermal imaging of conducting sapwood width enhances dendroecological studies in Southwestern U.S. conifers

Author
item LIBANTINO NORTON, CYNTHIA - University Of Arizona
item HU, JIA - University Of Arizona
item Scott, Russell
item BARRON-GAFFORD, GREG - University Of Arizona
item BABST, FLURIN - University Of Arizona

Submitted to: Trees
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2025
Publication Date: 11/8/2025
Citation: Libantino Norton, C., Hu, J., Scott, R.L., Barron-Gafford, G.A., Babst, F. 2025. Thermal imaging of conducting sapwood width enhances dendroecological studies in Southwestern U.S. conifers. Trees. 39. Article 118. https://doi.org/10.1007/s00468-025-02687-x.
DOI: https://doi.org/10.1007/s00468-025-02687-x

Interpretive Summary: USDA researchers in Tucson, AZ in collaboration with University researchers measure the movement of sap in trees to understand their water use (transpiration) in response to changes in weather and impacts of drought on forest health. To do this, they have developed a new technique to measure the amount of sap-carrying wood in tree stems. Based on this successful study, we encourage broad application of this user-friendly and species-independent method of quantifying sapwood width towards research on tree water use and growth.

Technical Abstract: Quantifying conducting sapwood width and area in trees facilitates studies of water and nutrient transport. Yet, distinguishing conducting from nonconducting xylem is not always straightforward due to the species-specific presence or absence of visible color differences. To improve field-based measurements, we present a novel method that uses a thermal infrared sensor to pinpoint the common temperature change at the transition between conducting and nonconducting xylem on increment cores. Sapwood width estimated this way matched the values obtained from the traditional “touch test” in Pinus ponderosa (PIPO; R2'='0.99) and Pinus strobiformis (PISF; R2'='0.98). A more rigorous evaluation against the visible color difference in Pseudotsuga menziesii (PSME) also resulted in an R2'='0.96. In a case study at the Mt. Bigelow flux-tower site (US-MtB, Arizona), we integrated these thermal sapwood measurements with observations of tree size, radial growth, and its climate sensitivity. PIPO had a larger sapwood (mean width'='7.6 cm) and exhibited less growth decrease under extreme drought compared to PSME (mean width'='4.7 cm). Conversely, PSME was the most productive species, hinting at its competitive strategy but also drought susceptibility under continued aridification. Based on this successful study, we encourage broad application of this user-friendly and species-independent method of quantifying sapwood width towards research on water, growth, and carbon dynamics.