BOREAS TE-11 Sap Flow Data Summary The BOREAS TE-11 team collected several data sets in support of its efforts to characterize and interpret information on the sap flow, gas exchange, and lichen photosynthesis of boreal vegetation and meteorological data of the area studied. This data set contains measurements of sap flow conducted at the SSA-OJP site in the growing seasons of 1993 and 1994. The data are stored in ASCII files. Table of Contents 1 Data Set Overview 2 Investigator(s) 3 Theory of Measurements 4 Equipment 5 Data Acquisition Methods 6 Observations 7 Data Description 8 Data Organization 9 Data Manipulations 10 Errors 11 Notes 12 Application of the Data Set 13 Future Modifications and Plans 14 Software 15 Data Access 16 Output Products and Availability 17 References 18 Glossary of Terms 19 List of Acronyms 20 Document Information 1. Data Set Overview This data set describes the sap flow measurements collected by Terrestrial Ecology (TE)-11 in the Southern Study Area (SSA). 1.1 Data Set Identification BOREAS TE-11 Sap Flow Data 1.2 Data Set Introduction The Terrestrial Ecology (TE)-11 team took measurements of sap flow were conducted at the BOReal Ecosystem-Atmosphere Study (BOREAS) SSA Old Jack Pine (OJP) site during the growing seasons of 1993 and 1994 using hand-made probes. 1.3 Objective/Purpose The purposes of the work were to: 1) Measure the average sap flow velocity in six trees. 2) Calculate the sap flow from the velocity and the sapwood area. 1.4 Summary of Parameters Sap flow measurements were taken at the SSA-OJP site on Julian days 236 to 245 in 1993 and Julian days 118 to 259 in 1994. Stand transpiration is computed in mm/hour for each of the measured trees. Sapwood area on TE-11's site was taken as 12.3 m2/ha. This figure may change according to new biometric data. 1.5 Discussion The TE-11 team's aim is to compare these data with a micrometeorological (micormet) estimate of tree transpiration (H20 flux above the forest minus H2O flux above the soil) If the comparison is good, these data will be used to fill out gaps that occurred when the micromet measurements were not operating. 1.6 Related Data Sets BOREAS TE-11 Leaf Gas Exchange Measurements 2. Investigator(s) 2.1 Investigator(s) Name and Title Bernard Saugier Professor 2.2 Title of Investigation Seasonal Variations of Net Photosynthesis and Transpiration at the Tree Level 2.3 Contact Information Contact 1: Bernard Saugier, Ecologie vegetale, bat. 362 Universite Paris-Sud Orsay cedex France 33.1.69.41.71.36 33.1.69.41.72.38 (fax) saugier@psisun.u-psud.fr Contact 2: Andrea Papagno Raytheon STX Corporation NASA GSFC Greenbelt, MD (301) 286-3134 (301) 286-0239 (fax) apapagno@pop900.gsfc.nasa.gov Contact 3: Shelaine Curd Raytheon STX Corporation NASA GSFC Greenbelt, MD (301) 286-2447 (301) 286-0239 (fax) shelaine.curd@gsfc.nasa.gov 3. Theory of Measurements Two cylindrical probes were inserted perpendicular to the tree trunk; one was continuously heated, while the other was not. Each probe contained a copper- constantan junction. The two constantan wires were connected together, and the voltage between the two copper wires was measured proportional to the temperature difference between the two probes. It was then transformed into an averaged sap velocity using a formula that was independent of the tree species. Then, sap flow was calculated as the product of sap velocity by the sapwood area. From these measurements, stand sapwood area was 12.3 m2/ha for a basal area of 22.5 m2/ha. Diameter of the probes: 2 mm. Length of the probes: 20 mm (usually). Resistance of the constantan wire: about 10 ohms. The temperature difference between the probes was about 12 °C during the night, and it decreased during the day. 4. Equipment 4.1 Sensor/Instrument Description The probes were made by Andre Granier, a coinvestigator, who went to the site in 1993 and in April 1994 to install the probes. They were connected to a CR10 data logger, downloaded to a portable PC. 4.1.1 Collection Environment None given. 4.1.2 Source/Platform None given. 4.1.3 Source/Platform Mission Objectives None given. 4.1.4 Key Variables Sap flow velocity, temperature difference, resistance, sap flow area. 4.1.5 Principles of Operation Two cylindrical probes were inserted perpendicular to the tree trunk; one was continuously heated, while the other was not. Each probe contained a copper-constantan junction. The two constantan wires were connected together, and we measured the voltage. between the two copper wires was measured proportional to the temperature difference between the two probes. It was then transformed into an averaged sap velocity using a formula that was independent of the tree species. Finally, sap flow was calculated as the product of sap velocity by the sapwood area. 4.1.6 Sensor/Instrument Measurement Geometry None given. 4.1.7 Manufacturer of Sensor/Instrument CR10 Data Logger Campbell Scientific, Inc. 815 West 1800 North Logan, UT 84321-1784 (435) 753-2342 (435) 750-9540 (fax) support@campbellsci.com The probes were made by Andre Granier, a coinvestigator. 4.2 Calibration No calibration was required in principle. The test will be the comparison with the micromet measurements (see above). 4.2.1 Specifications None given. 4.2.1.1 Tolerance None given. 4.2.2 Frequency of Calibration None given. 4.2.3 Other Calibration Information None given. 5. Data Acquisition Methods A Campbell Scientific, Inc., CR10 data logger was used for the acquisition and storage of data. Six channels were used in 1994. 6. Observations 6.1 Data Notes None given. 6.2 Field Notes The TE-11 team had fun and had no problems with this technique, which worked very well unattended for long periods. The only problem was with sensor 1, as mentioned in Section 10.1. 7. Data Description 7.1 Spatial Characteristics The six trees were about 20 m away from the TE scaffolding towers, in the direction of the micromet tower. The following table gives, for each tree, its circumference (C) at breast height (h) in mm and its approximate height in m. tree number C, mm h, m 1 256 10.50 2 331 11.25 3 362 13.25 4 368 12.75 5 435 13.50 6 521 14.70 7.1.1 Spatial Coverage At SSA-OJP. The six trees were about 20 m away from the TE scaffolding towers, in the direction of the micromet tower. The SSA measurement site and its associated North American Datum of 1983 (NAD83) coordinates are: OJP, site id G2L3T, Lat/Long: 53.91634° N, 104.69203° W, UTM Zone 13, N: 5974257.5, E: 520227.7. 7.1.2 Spatial Coverage Map Not available. 7.1.3 Spatial Resolution None given. 7.1.4 Projection None given. 7.1.5 Grid Description None given. 7.2 Temporal Characteristics 7.2.1 Temporal Coverage Measurements were taken every 15 minutes, from day 236 to day 245, in 1993, and measurements were taken every 30 minutes, from day 118 to day 259, in 1994. In 1994, the first data were not reliable because the sensors took some time to reach equilibrium and because alternating freezing and thawing gave strange results. In 1994, data were taken from day 120 and may not be very good until day 125. 7.2.2 Temporal Coverage Map None given. 7.2.3 Temporal Resolution None given. 7.3 Data Characteristics Data characteristics are defined in the companion data definition file (te11sapf.def). 7.4 Sample Data Record Sample data format shown in the companion data definition file (te11sapf.def). 8. Data Organization 8.1 Data Granularity All of the Sap Flow Data are contained in one dataset. 8.2 Data Format(s) The data files contain numerical and character fields of varying length separated by commas. The character fields are enclosed with a single apostrophe marks. There are no spaces between the fields. Sample data records are shown in the companion data definition file (te11sapf.def). 9. Data Manipulations 9.1 Formulae None. 9.1.1 Derivation Techniques and Algorithms The thermocouples gave an voltage representing the temperature difference DT. At present, there is no record of the absolute temperature of the trunk, so a constant factor was assumed for converting voltage to temperature difference: voltage in mV was multiplied by 25 to obtain DT in degrees Celsius. DT was called the actual temperature difference and DTM the maximum temperature difference (for a transpiration assumed to be zero). This was done directly in the program of the data logger. U, the average sap velocity, is computed as: U = 119*(DTM/DT-1)1.23 and is expressed in micrometers/second (1) \ F, the sap flow, is computed as: F = U*SA*AK, (2) where SA (sapwood area) is 1.23E-3 m2/m2, m2 of trunk per m2 of ground AK = 3600*1E-3 transforms micrometers per second into mm/hour 9.2 Data Processing Sequence The raw data were stored by the data logger. The data were then downloaded on the hard disk of a portable PC in a file named fluxseve.dat. This file was edited with Word for Windows, resulting in a file called fsevexxx.dat. Then a program called fsev94.bas produced an easy-to-read file called ojpstx_94.dat, containing raw data. This file was checked for errors and edited if necessary. The data were then processed by a program called dtmse294.bas, which computed the maximum nighttime values of DT (DTMAX), where DT is the temperature difference between the sensors. Then another program, dtmm.bas, computed a new set of DTMAX, in the following way. First, the local maxima of DTMAX were calculated, and then the new DTMAX were calculated by linear interpolation between these local maxima, and stored in a file called " dtmnx.dat". This procedure has the advantage of not taking into account nights during which a significant transpiration occurs, which leads to decreased (and erroneous) values of DTMAX. Finally, a program called fsevf394.bas computed sap flows from the raw data in file ojpstx.dat and from the DTMAX in the file called dtmnx.dat. The resultant sap flow files are called sapfx_94.dat (x=1 or 2). The two sap flow files were merged into a single file called sfojp94.dat (standing for Sap Flow of Old Jack Pine in 1994). The data from this final file were sent to BORIS. Raw data and intermediate data are available on request. 9.2.1 Processing Steps None given. 9.2.2 Processing Changes None given. 9.3 Calculations See Section 9.1.1. 9.3.1 Special Corrections/Adjustments None given. 9.3.2 Calculated Variables None given. 9.4 Graphs and Plots QuattroPro for windows was used to produce graphs. There is not an easy way to make them accessible (other than by giving the cumbersome QP files). Graphs produced were: - Diurnal values of sap flow and potential evaporation (computed from the metstation data and standard Penman formula). - The ratio of diurnal values of sap flow and potential evaporation, which increased from 0.1 in the beginning of May to a maximum of 0.3 in July and decreased to below 0.2 in mid-September. 10. Errors 10.1 Sources of Error One possible source is the accuracy in the measurement of the voltage, 250 to 500 microvolts. This did not seem to be a problem with the Campbell data logger. The second source is the assumption of a zero transpiration at night, necessary to get the maximum temperature difference DTM, and the drift of DTM with time. The above-described procedure should make the best use of the data. Another source of error may come from the sample of the six trees. These may not be representative of the tree stand. A comparison between an inventory made at TE-11's site in 1993 on only 100 trees, and an inventory by Bob Knox on a larger sample (50m * 50m) shows that TE-11's sample is relatively representative. Also, the value taken for the sapwood area (12.3 m2/ha) needs independent verification. TE-11 believes these data are fine when using daily values. The half-hourly values are also good, but there is a time lag between the values of branch transpiration (measured with branch bags) and sap flow values. This time lag is about 1 hour (maybe 1 hour and 15 minutes). Sap flow lags behind transpiration, so when using half-hourly values, subtract 1 hour from the time. The sensor (1) installed on the smallest tree did not work all the time, and TE- 11 did not use the data. In 1994, the first data were not reliable because the sensors took some time to reach equilibrium. The alternating freezing and thawing conditions gave strange results. In 1994, data were given from day 120, but may not be very good until day 125. 10.2 Quality Assessment A comparison will be done between the stand transpiration calculated by sap flow, and the difference between the latent heat fluxes above and below the forest canopy, as given by Dennis Baldocchi. 100 W/m2 = 0.15 mm/h. A preliminary comparison showed roughly the same values in 1994 as in 1993. The data file was checked for errors and edited as necessary. 10.2.1 Data Validation by Source None given. 10.2.2 Confidence Level/Accuracy Judgment None given. 10.2.3 Measurement Error for Parameters None given. 10.2.4 Additional Quality Assessments None given. 10.2.5 Data Verification by Data Center Data were examined for general consistency and clarity. 11. Notes None given. 11.1 Limitations of the Data None given. 11.2 Known Problems with the Data Only 2-cm sensors were used in 1994. It should be remembered that sap flow was measured at breast height, and this follows transpiration with a delay that is dependent on the variation in the amount of water stored by the trees. So although TE-11 believe that the maximum values and the diurnal values ae good, the instantaneous values should be used with care. A delay of about 1 hour between transpiration and sap flow variations was common (see above). 11.3 Usage Guidance See Sections 10.1 and 11.1. 11.4 Other Relevant Information The interpretation of the data requires knowledge of the variables affecting the evaporative demand: net radiation, saturation deficit, wind speed, and air temperature. These data are given in 1993 and 1994 by the mesomet station in Prince Albert (PA)-OJP. 12. Application of the Data Set These data can be used to obtain the sap flow rates for OJP in the SSA. 13. Future Modifications and Plans None given. 14. Software None given. 14.1 Software Description Word for Windows and QuattroPro were used. 14.2 Software Access None given. 15. Data Access None given. 15.1 Contact Information Ms. Beth Nelson BOREAS Data Manager NASA GSFC Greenbelt, MD (301) 286-4005 (301) 286-0239 (fax) Elizabeth.Nelson@gsfc.nasa.gov 15.2 Data Center Identification See Section 15.1. 15.3 Procedures for Obtaining Data Users may place requests by telephone, electronic mail, or fax. 15.4 Data Center Status/Plans The TE-11 sap flow data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The BOREAS contact at ORNL is: ORNL DAAC User Services Oak Ridge National Laboratory (865) 241-3952 ornldaac@ornl.gov ornl@eos.nasa.gov 16. Output Products and Availability 16.1 Tape Products None. 16.2 Film Products None. 16.3 Other Products Tabular ASCII files. 17. References 17.1 Satellite/Instrument/Data Processing Documentation None given. 17.2 Journal Articles and Study Reports Saugier B., A. Granier, J.Y. Pontailler, E. Dufrêne, and D.D. Baldocchi. 1997. Transpiration of a boreal pine forest measured by branch bags, sap flow and micrometeorological methods, Tree Physiology, 17, 511-519. Sellers, P.and F. Hall. 1994. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1994-3.0, NASA BOREAS Report (EXPLAN 94). Sellers, P., F. Hall, H. Margolis, B. Kelly, D. Baldocchi, G. den Hartog, J. Cihlar, M.G. Ryan, B. Goodison, P. Crill, K.J. Ranson, D. Lettenmaier, and D.E. Wickland. 1995. The boreal ecosystem-atmosphere study (BOREAS): an overview and earlyresults from the 1994 field year. Bulletin of the American Meteorological Society. 76(9):1549-1577. Sellers, P., F. Hall, and K.F. Huemmrich. 1996. Boreal Ecosystem-Atmosphere Study: 1994 Operations. NASA BOREAS Report (OPSDOC 94). Sellers, P.and F. Hall. 1996. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1996-2.0, NASA BOREAS Report (EXPLAN 96). Sellers, P., F. Hall, and K.F. Huemmrich. 1997. Boreal Ecosystem-Atmosphere Study: 1996 Operations. NASA BOREAS Report (OPSDOC 96). Sellers, P. J., F. G. Hall, R. D. Kelly, A. Black, D. Baldocchi, J. Berry, M. Ryan, K. J. Ranson, P. M. Crill, D. P. Lettenmaier, H. Margolis, J. Cihlar, J. Newcomer, D. Fitzjarrald, P. G. Jarvis, S. T. Gower, D. Halliwell, D. Williams, B. Goodison, D. E. Wickland, and F. E. Guertin, BOREAS in 1997: Experiment overview, scientific results, and future directions, Journal of Geophysical Research, 102 (D24), 28731-28769, 1997. 17.3 Archive/DBMS Usage Documentation None. 18. Glossary of Terms DT - The actual temperature difference between the probes. DTM - The maximum temperature difference between the probes. 19. List of Acronyms ASCII - American Standard Code for Information Interchange BOREAS - BOReal Ecosystem-Atmosphere Study BORIS - BOREAS Information System CD-ROM - Compact Disk-Read-Only Memory DAAC - Distributed Active Archive Center EOS - Earth Observing System EOSDIS - EOS Data and Information System GSFC - Goddard Space Flight Center HTML - HyperText Markup Language IFC - Intensive Field Campaign NAD83 - North American Datum of 1983 NASA - National Aeronautics and Space Administration NOAA - National Oceanic and Atmospheric Administration NSA - Northern Study Area OJP - Old Jack Pine ORNL - Oak Ridge National Laboratory PA - Prince Albert PANP - Prince Albert National Park SSA - Southern Study Area TE - Terrestrial Ecology URL - Uniform Resource Locator UTM - Universal Transverse Mercator 20. Document Information 20.1 Document Revision Date Date written: 06-Jan-1994 Last updated: 08-Oct-1998 20.2 Document Review Date(s) BORIS Review: 28-Jul-1998 Science Review: 12-Aug-1998 20.3 Document ID 20.4 Citation Dr. B. Saugier, of the Universite Paris-Sud, FRANCE 20.5 Document Curator 20.6 Document URL Keywords Sap flow rate Sapwood Temperature Velocity Xylem TE11_Sapflow.doc 10/09/98