Journal article
Drought Response in Three Conifer Species Detected by Sap Flow and Proximal Thermal Remote Sensing
Journal of geophysical research. Biogeosciences, Vol.130(9), e2025JG009127
09/2025
DOI: 10.1029/2025JG009127
Abstract
Dryland forests of the southwest United States face a warming and changing hydroclimate, yet our ability to monitor and predict vegetation‐drought dynamics over large regions remains limited. Here, we examine drought responses and predictability of sap flow for three species (Douglas fir, ponderosa pine, and southwestern white pine) over two consecutive years. We collected tree‐scale sap flow velocity and evaluated its relationship with soil water content (SWC) and vapor pressure deficit (VPD). Next, we identified the soil moisture threshold beyond which sap flow was no longer limited by SWC. We also assessed whether proximal remote sensing of canopy temperature and canopy‐to‐air temperature difference (ΔT) can capture ecosystem‐scale drought response dynamics. Significant sap flow reductions occurred in response to drought periods, but sap flow quickly recovered following large rainfall events. When SWC was below a threshold of ∼7% (cm 3 /cm 3 ), SWC and sap flow were positively correlated, indicating water‐limited conditions, while above this threshold, only VPD and sap flow were positively related, indicating atmospheric demand limited conditions. Species differences were minor, but ponderosa pine sap flow responded most rapidly to soil dehydration. ΔT was significantly correlated with sap flow, but the relationship switched from positive ( R = 0.73−0.94) during the pre‐ and post‐monsoon to negative during the monsoon ( R = −0.31−0.48). This shift likely reflects a transition from soil moisture supply to atmospheric demand limitation during wetter periods. These findings highlight the potential of combining tree‐scale sap flow measurements with thermal remote sensing to enhance understanding of vegetation‐drought dynamics in dryland forests.
Forest trees are increasingly facing changes in rainfall patterns and rising temperatures. Our ability to track and predict how trees respond to these changes, however, is still limited. In this study, we measured tree water use over two contrasting years in a mountain‐top evergreen forest in Arizona, USA. We found that once soil moisture exceeds a certain threshold (∼7%), the trees were no longer limited by soil moisture supply but by atmospheric dryness conditions. Additionally, we assessed whether proximal remote sensing of canopy temperature and canopy‐to‐air temperature difference (ΔT) can capture ecosystem‐scale drought response dynamics. We revealed that ΔT was significantly correlated with sap flow, but that the relationship switched from positive to negative due to the conditions in different seasons. This research shows how combining tree measurements with data from thermal cameras to measure canopy temperatures improves our ability to monitor forest response to drought on a larger scale.
A dry 2023 monsoon reduced sap flow of three montane conifers in southeast Arizona, Pinus ponderosa was most senstive and Pinus strobiformis least sensitive to water stress Sap flow of all species responded positively to VPD when soil moisture exceeded 7% Canopy‐to‐air temperature difference (ΔT) correlated significantly with sap flow, however the relationship switched from positive to negative during the monsoon period
Details
- Title: Subtitle
- Drought Response in Three Conifer Species Detected by Sap Flow and Proximal Thermal Remote Sensing
- Creators
- Daphna Uni - University of ArizonaRussell L. Scott - Southwest Watershed Research CenterMostafa Javadian - University of ArizonaJoel Biederman - University of ArizonaMatthew P. Dannenberg - University of IowaWilliam K. Smith - University of Arizona
- Resource Type
- Journal article
- Publication Details
- Journal of geophysical research. Biogeosciences, Vol.130(9), e2025JG009127
- DOI
- 10.1029/2025JG009127
- ISSN
- 2169-8953
- eISSN
- 2169-8961
- Publisher
- AMER GEOPHYSICAL UNION
- Grant note
- Catalina-Jemez Critical Zone Observatory
This research would not have been possible without the major efforts of G. Barron-Gafford (site PI) and P. Murphy (technician) to curate long-term measurements at the Mount Bigelow site. We are also grateful for J. Wong at USDA ARS, who played a key role in the installation and maintenance of the Mount Bigelow thermal camera. We would like to thank Dr. E. Gallo, Dr. J. Guo and Dr. F. Zhang for helpful discussions. We acknowledge funding for this research provided by the NASA Carbon Cycle Science Program (Grant 80NSSC23K0109) and the United States Department of Agriculture (USDA; cooperative agreement number 58-2022-2-001). WKS and MPD additionally acknowledge support provided by NASA Grant 80NSSC20K1805. DU acknowledge the BARD (The United States-Israel Binational Agricultural Research and Development Fund) for supporting their time on the project (FI-634-2023#). Mt. Bigelow operation and maintenance support was provided by National Science Foundation EAR awards 0724958 and 1331408 to the Catalina-Jemez Critical Zone Observatory.
- Language
- English
- Date published
- 09/2025
- Academic Unit
- Geographical and Sustainability Sciences
- Record Identifier
- 9984958288902771
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