Rafael Poyatos, Working Group Chair, February 2026
At the global scale, the amount of water transpired by plants exceeds that transported by all rivers to the oceans. This water flux from the soil to the atmosphere is strongly regulated by plants in order to maintain a favorable water status. This regulation of plant water economy is highly diverse across and within species and strongly influences plant productivity and survival. Quantifying plant water transport and status is therefore essential to understand how natural ecosystems and crops respond to dynamic changes in water availability and to assess stress responses in general.
The ISHS Working Group Sensing Water Status originated from a community of scientists and practitioners interested in measuring plant water transport, mostly using so-called sap flow methods. Thermometric sap flow methods are currently the most widely used approach for continuously quantifying plant water transport in the field. Nowadays, sap flow methods are often combined with other techniques that provide additional information on plant water status, such as manual or continuous water potential measurements, stem diameter variations using digital dendrometry, or stem water content measurements based on the electrical properties of wood.
More recently, numerous data streams on plant water transport and plant water status have become available in global databases that can be used by the scientific community. In the coming years, these initiatives will likely continue to grow and new ones will emerge, highlighting the potential of sharing data, protocols, and data-processing routines to promote data reuse for synthesis and modeling activities that improve our understanding of vegetation functioning and inform crop management.
Below, we provide an updated list (February 2026) of scientific papers, websites, and software that offer basic information on measurements of plant water flow and plant water status, including their methodological foundations, data-processing resources, current global databases and initiatives, and a list of manufacturers. This list is likely biased toward more recent sources, but the review papers include references to earlier work on which recent developments are based.
1. Methods
1.1. Sap flow
Baker, J. M., & Van Bavel, C. H. M. (1987). Measurement of mass flow of water in the stems of herbaceous plants. Plant, Cell & Environment, 10(9), 777–782. https://doi.org/10.1111/1365-3040.ep11604765
Čermák, J., Kučera, J., & Nadezhdina, N. (2004). Sap flow measurements with some thermodynamic methods, flow integration within trees and scaling up from sample trees to entire forest stands. Trees, 18(5), 529–546. https://doi.org/10.1007/s00468-004-0339-6
Cohen, Y., Fuchs, M., & Green, G. C. (1981). Improvement of the heat pulse method for determining sap flow in trees. Plant, Cell & Environment, 4(5), 391–397. https://doi.org/10.1111/j.1365-3040.1981.tb02117.x
Edwards, W. R. N., Becker, P., & Čermák, J. (1996). A unified nomenclature for sap flow measurements. Tree Physiology, 17, 65–67.
Forster, M. A. (2019). The Dual Method Approach (DMA) Resolves Measurement Range Limitations of Heat Pulse Velocity Sap Flow Sensors. Forests, 10(1), 46. https://doi.org/10.3390/f10010046
Green, S., Clothier, B., & Jardine, B. (2003). Theory and Practical Application of Heat Pulse to Measure Sap Flow. Agronomy Journal, 95(6), 1371–1379. https://doi.org/10.2134/agronj2003.1371
Köstner, B., Granier, A., & Cermák, J. (1998). Sapflow measurements in forest stands: Methods and uncertainties. Annales Des Sciences Forestières, 55(1–2), 13–27. https://doi.org/10.1051/forest:19980102
Kučera, J., Čermák, J., & Penka, M. (1977). Improved thermal method of continual recording the transpiration flow rate dynamics. Biologia Plantarum (Praha), 19(6), 413–420.
Lemeur, R., Fernández, J. E., & Steppe, K. (2009). Symbols, SI units and physical quantities within the scope of sap flow studies. Acta Horticulturae, 846, 21–32. https://doi.org/10.17660/ActaHortic.2009.846.0
López‐Bernal Álvaro, Testi Luca, & Villalobos Francisco J. (2017). A single‐probe heat pulse method for estimating sap velocity in trees. New Phytologist, 216(1), 321–329. https://doi.org/10.1111/nph.14694
Lu, P., Urban, L., & Ping, Z. (2004). Granier’s thermal dissipation probe (TDP) method for measuring sap flow in trees: Theory and practice. Acta Botanica Sinica, 46, 631–646.
Marshall, D. C. (1958). Measurement of Sap Flow in Conifers by Heat Transport. Plant Physiology, 33(6), 385–396. https://doi.org/10.1104/pp.33.6.385
Nadezhdina, N. (2018). Revisiting the Heat Field Deformation (HFD) method for measuring sap flow. iForest – Biogeosciences and Forestry, 11(1), 118–130. (world). https://doi.org/10.3832/ifor2381-011
Ren, R., von der Crone, J., Horton, R., Liu, G., & Steppe, K. (2020). An improved single probe method for sap flow measurements using finite heating duration. Agricultural and Forest Meteorology, 280, 107788. https://doi.org/10.1016/j.agrformet.2019.107788
Sakuratani, T. (1981). A Heat Balance Method for Measuring Water Flux in the Stem of Intact Plants. Journal of Agricultural Meteorology, 37(1), 9–17. https://doi.org/10.2480/agrmet.37.9
Siqueira, J. M., & Ferreira, M. I. (2020). Optimisation of CAG technique: An algorithm to estimate low and reverse sap flow in roots. Agricultural and Forest Meteorology, 294, 108129. https://doi.org/10.1016/j.agrformet.2020.108129
Smith, D., & Allen, S. (1996). Measurement of sap flow in plant stems. J. Exp. Bot., 47(305), 1833–1844.
Swanson, R. H. (1994). Significant historical developments in thermal methods for measuring sap flow in trees. Agricultural and Forest Meteorology, IUFRO Centennial Issue: Global Climate Change and Applied Forest Hydrology, 72(1), 113–132. https://doi.org/10.1016/0168-1923(94)90094-9
Testi, L., & Villalobos, F. J. (2009). New approach for measuring low sap velocities in trees. Agricultural and Forest Meteorology, 149(3–4), 730–734. https://doi.org/10.1016/j.agrformet.2008.10.015
Vandegehuchte, M. W., & Steppe, K. (2012). Sapflow+: A four-needle heat-pulse sap flow sensor enabling nonempirical sap flux density and water content measurements. New Phytologist, 196(1), 306–317. https://doi.org/10.1111/j.1469-8137.2012.04237.x
Vandegehuchte, M. W., & Steppe, K. (2013). Sap-flux density measurement methods: Working principles and applicability. Functional Plant Biology, 40(3), 213–223. https://doi.org/10.1071/FP12233
Wang, J., Turner, N. C., Feng, H., Dyck, M., & He, H. (2023). Heat tracer-based sap flow methods for tree transpiration measurements: A mini review and bibliometric analysis. Journal of Experimental Botany, 74(3), 723–742. https://doi.org/10.1093/jxb/erac424
1.2. Water potentials
Rodriguez-Dominguez, C. M., Forner, A., Martorell, S., Choat, B., Lopez, R., Peters, J. M. R., Pfautsch, S., Mayr, S., Carins-Murphy, M. R., McAdam, S. A. M., Richardson, F., Diaz-Espejo, A., Hernandez-Santana, V., Menezes-Silva, P. E., Torres-Ruiz, J. M., Batz, T. A., & Sack, L. (2022). Leaf water potential measurements using the pressure chamber: Synthetic testing of assumptions towards best practices for precision and accuracy. Plant, Cell & Environment, 45(7), 2037–2061. https://doi.org/10.1111/pce.14330
Scholander, P. F., Hammel, H. T., Bradstreet, E. D., & Hemmingsen, E. A. (1965). Sap pressure in vascular plants. Science, 148, 339–346.
Zweifel, R., Zimmerman, L., & Newberry, D. M. (2005). Modeling tree water deficit from microclimate: An approcah to quantifying drought water stress. Tree Physiology, 25, 147–156.
1.3. Dendrometry
Bourbia, I., & Brodribb, T. J. (2023). A new technique for monitoring plant transpiration under field conditions using leaf optical dendrometry. Agricultural and Forest Meteorology, 331, 109328. https://doi.org/10.1016/j.agrformet.2023.109328
de Belder, A. (2016). Comparison of different dendrometers and LVDT-sensors in laboratory and field condition. Retrieved November 18, 2016, from http://lib.ugent.be/fulltxt/RUG01/002/217/207/RUG01-002217207_2015_0001_AC.pdf
Irvine, J., & Grace, J. (1997). Continuous measurements of water tensions in the xylem of trees based on the elastic properties of wood. Planta, 202(4), 455–461. https://doi.org/10.1007/s004250050149
Zweifel, R., & Häsler, R. (2001). Dynamics of water storage in mature subalpine Picea abies: Temporal and spatial patterns of change in stem radius. Tree Physiology, 21(9), 561–569. https://doi.org/10.1093/treephys/21.9.561
Zweifel, R., Haeni, M., Buchmann, N., & Eugster, W. (2016). Are trees able to grow in periods of stem shrinkage? New Phytologist, 211(3), 839–849. https://doi.org/10.1111/nph.13995
Zweifel, R., Item, H., & Häsler, R. (2000). Stem radius changes and their relation to stored water in stems of young Norway spruce trees. Trees, 15, 50–57. https://doi.org/10.1007/s004680000072
1.4. Stem water content
He, H., Turner, N. C., Aogu, K., Dyck, M., Feng, H., Si, B., Wang, J., & Lv, J. (2021). Time and frequency domain reflectometry for the measurement of tree stem water content: A review, evaluation, and future perspectives. Agricultural and Forest Meteorology, 306, 108442. https://doi.org/10.1016/j.agrformet.2021.108442
Irvine, J., & Grace, J. (1997). Non-destructive measurement of stem water content by time domain reflectometry using short probes. Journal of Experimental Botany, 48(3), 813–818. https://doi.org/10.1093/jxb/48.3.813
Matheny, A. M., Bohrer, G., Garrity, S. R., Morin, T. H., Howard, C. J., & Vogel, C. S. (2015). Observations of stem water storage in trees of opposing hydraulic strategies. Ecosphere, 6(9), 1–13. https://doi.org/10.1890/ES15-00170.1
Wullschleger, S. D., Hanson, P. J., & Todd, D. E. (1996). Measuring stem water content in four deciduous hardwoods with a time-domain reflectometer. Tree Physiology, 16(10), 809–815. https://doi.org/10.1093/treephys/16.10.809
2. Global databases
Poyatos, R., Granda, V., Flo, V., Adams, M. A., Adorján, B., Aguadé, D., Aidar, M. P. M., Allen, S., Alvarado-Barrientos, M. S., Anderson-Teixeira, K. J., Aparecido, L. M., Arain, M. A., Aranda, I., Asbjornsen, H., Baxter, R., Beamesderfer, E., Berry, Z. C., Berveiller, D., Blakely, B., … Martínez-Vilalta, J. (2021). Global transpiration data from sap flow measurements: The SAPFLUXNET database. Earth System Science Data, 13(6), 2607–2649. https://doi.org/10.5194/essd-13-2607-2021
PSInet: A global water potential network – PSInet. (n.d.). Retrieved February 12, 2026, from https://psinetrcn.github.io/
Restrepo-Acevedo, A. M., Guo, J. S., Kannenberg, S. A., Benson, M. C., Beverly, D., Diaz, R., Anderegg, W. R. L., Johnson, D. M., Koch, G., Konings, A. G., Lowman, L. E. L., Martínez-Vilalta, J., Poyatos, R., Schenk, H. J., Matheny, A. M., McCulloh, K. A., Nippert, J. B., Oliveira, R. S., & Novick, K. (2024). PSInet: A new global water potential network. Tree Physiology, 44(10), tpae110. https://doi.org/10.1093/treephys/tpae110
SAPFLUXNET Project. (2026.). SAPFLUXNET Project. Retrieved February 12, 2026, from https://sapfluxnet.creaf.cat/
3. Data processing and calibration tools
Dix, M. J., & Aubrey, D. P. (2021a). Calibration approach and range of observed sap flow influences transpiration estimates from thermal dissipation sensors. Agricultural and Forest Meteorology, 307, 108534. https://doi.org/10.1016/j.agrformet.2021.108534
Dix, M. J., & Aubrey, D. P. (2021b). Recalibrating Best Practices, Challenges, and Limitations of Estimating Tree Transpiration Via Sap Flow. Current Forestry Reports. https://doi.org/10.1007/s40725-021-00134-x
Flo, V., Martinez-Vilalta, J., Steppe, K., Schuldt, B., & Poyatos, R. (2019). A synthesis of bias and uncertainty in sap flow methods. Agricultural and Forest Meteorology, 271, 362–374. https://doi.org/10.1016/j.agrformet.2019.03.012
Fuchs, S., Leuschner, C., Link, R., Coners, H., & Schuldt, B. (2017). Calibration and comparison of thermal dissipation, heat ratio and heat field deformation sap flow probes for diffuse-porous trees. Agricultural and Forest Meteorology, 244–245, 151–161. https://doi.org/10.1016/j.agrformet.2017.04.003
Granda, V., Poyatos, R., Flo, V., Nelson, J., & Team, S. C. (2019). sapfluxnetr: Working with “Sapfluxnet” Project Data (Version 0.0.7) [Computer software]. https://CRAN.R-project.org/package=sapfluxnetr
Knüsel, S., Peters, R. L., Haeni, M., Wilhelm, M., & Zweifel, R. (2021). Processing and Extraction of Seasonal Tree Physiological Parameters from Stem Radius Time Series. Forests, 12(6), Article 6. https://doi.org/10.3390/f12060765
Martius, L. R., Mencuccini, M., Bittencourt, P. R. L., Moraes Alves, M., Binks, O., Sanchez-Martinez, P., da Costa, A. C. L., & Meir, P. (2024). Towards accurate monitoring of water content in woody tissue across tropical forests and other biomes. Tree Physiology, 44(8), tpae076. https://doi.org/10.1093/treephys/tpae076
Matheny, A. M., Garrity, S. R., & Bohrer, G. (2017). The Calibration and Use of Capacitance Sensors to Monitor Stem Water Content in Trees. JoVE (Journal of Visualized Experiments), (130), e57062. https://doi.org/10.3791/57062
Oishi, A. C., Hawthorne, D. A., & Oren, R. (2016). Baseliner: An open-source, interactive tool for processing sap flux data from thermal dissipation probes. SoftwareX. https://doi.org/10.1016/j.softx.2016.07.003
Peters, R. L., Pappas, C., Hurley, A. G., Poyatos, R., Flo, V., Zweifel, R., Goossens, W., & Steppe, K. (2021). Assimilate, process and analyse thermal dissipation sap flow data using the TREX r package. Methods in Ecology and Evolution, 12(2), 342–350. https://doi.org/10.1111/2041-210X.13524
Speckman, H., Ewers, B. E., & Beverly, D. P. (2020). AquaFlux: Rapid, transparent and replicable analyses of plant transpiration. Methods in Ecology and Evolution, 11(1), 44–50. https://doi.org/10.1111/2041-210X.13309
Steppe, K., De Pauw, D. J. W., Doody, T. M., & Teskey, R. O. (2010). A comparison of sap flux density using thermal dissipation, heat pulse velocity and heat field deformation methods. Agricultural and Forest Meteorology, 150(7–8), 1046–1056. https://doi.org/10.1016/j.agrformet.2010.04.004
Wang, J., & Renninger, H. J. (2025). SapFlower: An automated tool for sap flow data preprocessing, gap-filling, and analysis using deep learning. New Phytologist, 246(5), 2324–2345. https://doi.org/10.1111/nph.70107
Wimmler, M.-C., Nadezhdina, N., Bowen, H., Alvarado-Barrientos, S., David, T., Fontenla-Razzetto, G., Kniesel, B., Lange, H., Link, R. M., Liu, Y., López-Portillo, J., Pinto, C., Zhao, J., & Vovides, A. G. (2024). Sap Flow Analyzer: A tool to standardize sap flow estimation and scaling to whole-tree water use using the HFD method. Methods in Ecology and Evolution, 15(9), 1532–1539. https://doi.org/10.1111/2041-210X.14392
4. Manufacturers (not exhaustive)
Dynagage Sap Flow Sensor—Dynamax. (n.d.). Retrieved February 12, 2026, from https://www.dynamax.com/products/transpiration-sap-flow/dynagage-sap-flow-sensor
East 30 Sensors. (n.d.). Mysite. Retrieved February 12, 2026, from https://www.east30sensors.com
ICT International Products. (n.d.). ICT International. Retrieved February 12, 2026, from https://ictinternational.com/products/
Main page—EMS Brno. (n.d.). Retrieved February 12, 2026, from https://www.emsbrno.cz/p.axd/en/Main.Page.html
Natkon Dendrometers. (n.d.). Natkon Dendrometers. Retrieved February 12, 2026, from https://natkon.ch/
Point Dendrometer | TOMST. (n.d.). Retrieved February 12, 2026, from https://tomst.com/web/en/systems/tms/point-dendrometer/
Products. (n.d.). Implexx. Retrieved February 12, 2026, from https://www.implexx.io/products/
Products | Ecomatik GmbH. (n.d.). Retrieved February 12, 2026, from https://ecomatik.de/en/products/
TEROS 11—METER Group. (n.d.). Retrieved February 12, 2026, from https://metergroup.com/products/teros-11/
5. Sensor construction
Davis, T. W., Kuo, C.-M., Liang, X., & Yu, P.-S. (2012). Sap Flow Sensors: Construction, Quality Control and Comparison. Sensors, 12(1), 954–971. https://doi.org/10.3390/s120100954
James, S. A., Clearwater, M. J., Meinzer, F. C., & Goldstein, G. (2002). Heat dissipation sensors of variable length for the measurement of sap flow in trees with deep sapwood. Tree Physiology, 22(4), 277–283.
Jones, T. S., Winbourne, J. B., & Hutyra, L. R. (2020). Ribbonized sap flow: An emerging technology for the integration of sap flow sensor components onto a single platform. Ecosphere, 11(6), e03135. https://doi.org/10.1002/ecs2.3135
Miner, G. L., Ham, J. M., & Kluitenberg, G. J. (2017). A heat-pulse method for measuring sap flow in corn and sunflower using 3D-printed sensor bodies and low-cost electronics. Agricultural and Forest Meteorology, 246, 86–97. https://doi.org/10.1016/j.agrformet.2017.06.012