BOREAS TE-06 Predawn Leaf Water Potentials and Foliage Moisture Content Summary The BOREAS TE-06 team collected several data sets to examine the influence of vegetation, climate, and their interactions on the major carbon fluxes for boreal forest species. This data set contains summaries of predawn leaf water potentials and foliage moisture contents collected at the TF and CEV sites that had canopy access towers. The data was collected on a nearly weekly basis from early June to late August 1994 by TE-06, members of the BOREAS staff, and employees of Environment Canada. The data are provided in tabular 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 1.1 Data Set Identification BOREAS TE-06 Predawn Leaf Water Potentials and Foliage Moisture Contents 1.2 Data Set Introduction The data referenced in this documentation are summaries of predawn leaf water potentials and foliage moisture contents collected at the BOReal Ecosystem- Atmosphere Study (BOREAS) Tower Flux (TF) and Carbon Evaluation (CEV) sites that had canopy access towers. The data was collected on a nearly weekly basis from early June to late August 1994. This data set provides an assessment of the water status of key tree species at sites were physiological measurements were being made. 1.3 Objective/Purpose The objective of this study was to provide an assessment of the water status of key tree species at sites were physiological measurements were being made. 1.4 Summary of Parameters predawn leaf water potential foliage moisture content 1.5 Discussion Predawn leaf water potential has long been assumed to be a good indicator of the hydrological status of trees. Essentially, the matric potential of tree foliage is assumed to come into equilibrium with the matric potential of the soil over the course of an evening. An increase or decrease in the matric potential of the soil reflects an increase or decrease in available water for plant transpiration. This equilibrium between the soil and foliage matric potentials may also be reflected in the foliage moisture content. 1.6 Related Data Sets BOREAS TE-06 1996 Soil and Air Temperatures in the NSA BOREAS TE-06 Allometry Data 2. Investigator(s) 2.1 Investigator(s) Name and Title Tom Gower, Professor University of Wisconsin-Madison 2.2 Title of Investigation Predawn leaf water potentials and foliage moisture contents in boreal forest trees. 2.3 Contact Information Contact 1 ---------------- Tom Gower University of Wisconsin-Madison Madison WI (608) 262-0532 stgower@facstaff.wisc.edu Contact 2 ------------- Jason G Vogel University of Wisconsin-Madison Madison WI (608) 262 6369 vogel@calshp.cals.wisc.edu 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 Predawn leaf water potential has long been assumed to be a good indicator of the hydrological status of trees. Essentially, the matric potential of tree foliage is assumed to come into equilibrium with the matric potential of the soil over the course of an evening. An increase or decrease in the matric potential of the soil reflects an increase or decrease in available water for plant transpiration. This equilibrium between the soil and foliage matric potentials may also be reflected in the foliage moisture content. The foliar matric potential is measured by determining the pressure required to remove water from the foliage of a small foliated twig that has been removed from the upper portion of the tree. 4. Equipment: 4.1 Sensor/Instrument Description shotgun (12 gauge), pressure bomb 4.1.1 Collection Environment The measurements were taken under various climatic conditions on the given sampling days. Measurements were not made during evenings that had experienced a substantial rain event because this may cause a re-equilibration of the trees with the soil that would not be captured by a single predawn measurement. 4.1.2 Source/Platform All samples were collected from canopy access towers or the ground. 4.1.3 Source/Platform Mission Objectives Not applicable. 4.1.4 Key Variables Not applicable. 4.1.5 Principles of Operation The sample foliage is secured in an airtight chamber that is attached to a pressure gauge and a gas source. The pressure in the chamber is increased while the pressure gauge and the foliage tip are being watched. When water/sap begins to ìoozeî from the foliage it is considered to be at equilibrium with pressure in the chamber, and this pressure is recorded as the predawn leaf water potential. 4.1.6 Sensor/Instrument Measurement Geometry Not applicable. 4.1.7 Manufacturer of Sensor/Instrument Pressure Bomb PMS Instruments Inc. 2750 NW Royal Oaks Dr Corvallis OR, 97330 (503) 752 7926 4.2 Calibration 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 foliage sample was shot down from the southfacing upper one-third of a canopy in the early morning hours before sunrise. The sample foliage was secured in an airtight chamber that was attached to a pressure gauge and a gas source. The pressure in the chamber was increased while the gauge and the tip of the foliage are being watched. When water/sap begins to ooze from the foliage it was considered to be at equilibrium with pressure in the chamber, and this pressure was recorded as the predawn leaf water potential. 6. Observations 6.1 Data Notes None given 6.2 Field Notes None given 7. Data Description 7.1 Spatial Characteristics 7.1.1 Spatial Coverage Foliage samples were collected as close to the tower as possible, but generally at least 50 m from the tower to assure that no stray shotgun BBís interfered with instruments or sleepy researchers operating on the towers. SITE LATITUDE LONGITUDE ------------- ---------- ---------- NSA-UBS 55.90802 N 98.51865 W NSA-OA 55.88691 N 98.67479 W NSA-OBS 55.88007 N 98.48139 W NSA-OJP 55.92842 N 98.62396 W NSA-OJP 55.92842 N 98.62396 W NSA-YJP 55.89575 N 98.28706 W SSA-OA 53.62889 N 106.19779 W SSA-YA 53.65601 N 105.32314 W SSA-MIX 53.7254 N 105.20643 W SSA-OBS 53.98717 N 105.11779 W SSA-OJP 53.91634 N 104.69203 W SSA-YJP 53.87581 N 104.64529 W 7.1.2 Spatial Coverage Map Not available. 7.1.3 Spatial Resolution The data represent point source measurements from the sample locations. 7.1.4 Projection Not applicable. 7.1.5 Grid Description Not applicable. 7.2 Temporal Characteristics 7.2.1 Temporal Coverage The measurements began in mid-June and continued approximately weekly through the summer until late-August and early September of 1994. Start and end times varied between the SSA and NSA. Specific dates are included in the data set. 7.2.2 Temporal Coverage Map Not available. 7.2.3 Temporal Resolution We attempted to make the measurements within 10 days of one another in order to make possible some degree of interpolation. 7.3 Data Characteristics Data characteristics are defined in the companion data definition file (te6h2opd.def). 7.4 Sample Data Record Sample data format shown in the companion data definition file (te6h2opd.def). 8. Data Organization 8.1 Data Granularity All of the Predawn Leaf Water Potentials and Foliage Moisture Content data are contained in one dataset. 8.2 Data Format(s) The data files contain a series of numerical and character fields of varying length separated by commas. The character fields are enclosed in single apostrophe marks. Sample data records are shown in the companion data definition file (te6h2opd.def). 9. Data Manipulations 9.1 Formulae 9.1.1 Derivation Techniques and Algorithms Not applicable. 9.2 Data Processing Sequence 9.2.1 Processing Steps None. 9.2.2 Processing Changes None. 9.3 Calculations 9.3.1 Special Corrections/Adjustments Not applicable. 9.3.2 Calculated Variables The mean foliage moisture content = (wet weight-dry weight)/dry weight. 9.4 Graphs and Plots Not applicable. 10. Errors 10.1 Sources of Error There are a number of sources of error that can occur when making this measurement. In conifers, resins may obscure the exuding sap resulting in overestimation of LWP. During the long periods of twilight (June 16-June 27) there is the potential that the stomata of the leaves will not close long enough for the foliage to equilibrate with the soil. Unfortunately there is no way to directly test this, but we suspect the large variability seen during this period may have been the result of such a phenomena. Operator error is also a common feature of this measurement because of its interpretative nature. Finally there is variability between tree species in the pressure bombs efficacy in describing an actual LWP (Kramer 1983), we did not find anything in the literature in regards to these species and did not test the method but did test our measurements against soil moisture measurements where the latter were available (see 10.2.1). 10.2 Quality Assessment The data provided are of generally good quality with an increasing level of precision and accuracy from early to late summer. The LWP measurement for aspen more closely agreed with soil moisture than did jack pine. No soil moisture data were found for black spruce so no comparison was made. 10.2.1 Data Validation by Source We compared the predawn leaf water potentials to soil tension measurements made with gypsum blocks at NOJP and SOA. Agreement between the two measurements were very good for aspen, but only fair for the jack pine. No comparison was possible for black spruce. 10.2.2 Confidence Level/Accuracy Judgment Confidence level for the aspen sites is high and fair for the jack pine sites when the objective is the water status of the plant. An evaluation of the black spruce measurements cannot be made. Researchers should note 10.1. 10.2.3 Measurement Error for Parameters Not applicable. 10.2.4 Additional Quality Assessments Not applicable. 10.2.5 Data Verification by Data Center Data were examined for general consistency and clarity. 11. Notes 11.1 Limitations of the Data Not applicable. 11.2 Known Problems with the Data See section 10.2. 11.3 Usage Guidance None. 11.4 Other Relevant Information None. 12. Application of the Data Set Assessment of the water status of tree species in the boreal forest. 13. Future Modifications and Plans None. 14. Software 14.1 Software Description Not applicable. 14.2 Software Access Not applicable. 15. Data Access 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-06 leaf water potential 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 The data are available in tabular ASCII files. 17. References 17.1 Platform/Sensor/Instrument/Data Processing Documentation Kramer PJ. 1983. Water relations of plants. Academic press. pp 384-387. 17.2 Journal Articles and Study Reports Sellers, P. and F. Hall. 1994. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1994-3.0, NASA BOREAS Report (EXPLAN 94). Sellers, P. and F. Hall. 1996. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1996-2.0, NASA BOREAS Report (EXPLAN 96). Sellers, P. and F. Hall. 1997. BOREAS Overview Paper. JGR Special Issue. Sellers, P., F. Hall, and K.F. Huemmrich. 1996. Boreal Ecosystem-Atmosphere Study: 1994 Operations. NASA BOREAS Report (OPS DOC 94). Sellers, P., F. Hall, and K.F. Huemmrich. 1997. Boreal Ecosystem-Atmosphere Study: 1996 Operations. NASA BOREAS Report (OPS DOC 96). 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 early results from the 1994 field year. Bulletin of the American Meteorological Society. 76(9):1549-1577. 17.3 Archive/DBMS Usage Documentation None. 18. Glossary of Terms None. 19. List of Acronyms BOREAS - BOReal Ecosystem-Atmosphere Study BORIS - BOREAS Information System BS - Black Spruce CEV - Carbon Evaluation Site DAAC - Distributed Active Archive Center EOS - Earth Observing System EOSDIS - EOS Data and Information System LWP - Leaf water potential GSFC - Goddard Space Flight Center MIX - Mixed Stand NSA - Northern Study Area OA - Old Aspen OBS - Old Black Spruce OJP - Old Jack Pine ORNL - Oak Ridge National Laboratory SSA - Southern Study Area TF - Tower flux site URL - Uniform Resource Locator WAB - Wind aligned blob YJP - Young Jack Pine 20. Document Information 20.1 Document Revision Date Written: 30-Jun-1998 Last Updated: 01-Jul-1998 20.2 Document Review Date(s) BORIS Review: 30-Jun-1998 Science Review: 20.3 Document 20.4 Citation Please contact Investigators listed in Section 2.3. 20.5 Document Curator 20.6 Document URL Keywords Water potential Foliage moisture content TE06_Leaf_Water_Pot.doc 07/07/98