BOREAS RSS-17 Xylem Flux Density Measurements at the SSA-OBS Site Summary As part of its efforts to determine environmental and phenological states from radar imagery, the BOREAS RSS-17 team collected in situ tree xylem flow measurements for one growing season on five Picea mariana (black spruce) trees. The data were collected to obtain information on the temporal and spatial variability in water uptake by trees in the SSA-OBS (Picea mariana) stand in the BOREAS SSA. Temporally, the data were collected in 30-minute intervals for 120 days from 31-May-1994 until 27-September-1994. The data are stored 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 RSS-17 Xylem Flux Density Measurements at the SSA-OBS Site 1.2 Data Set Introduction This data set consists of continuous, in situ tree xylem sap flow measurements on five black spruce trees at the Old Black Spruce (OBS) tower site, located in the BOReal Ecosystem-Atmosphere Study (BOREAS) Southern Study Area (SSA), near Candle Lake, Saskatchewan, Canada. Xylem sap flux was measured continuously from 31-May-1994 until 27-September-1994. The five trees measured were located near the main tower at the BOREAS SSA-OBS site in a mixed Picea mariana/Larix laricina/Pinus banksiana stand approximately 10-20 m from the main tower site hut. Picea mariana was the dominating tree species in the stand. All five trees measured were Picea mariana (black spruce) of varying tree dimensions. Tree xylem sap flow was measured with a thermal constant energy input method (Granier, 1992), which consists of an inversely connected pair of copper- constantane thermocouples and a heated probe that releases 200 mWatt on a probe length of 20 mm. Tree xylem flux was measured in the tree bole between 1.55 and 1.8 m height above the moss layer. Each tree had a heated probe of 20 mm in length and 2 mm in diameter inserted horizontally into the stem. Insertion depth was from the cambium layer on 20 mm into the xylem. The xylem sap flow measurements were logged automatically by a data logger (Delta-T DL-2). The data points stored indicate the average of measurements for a time interval between two data storage points. Storage time is indicated as the time at the end of each measurement/averaging interval. Data from the thermocouple pair were postprocessed to obtain the heat flux density of the xylem water passing the inserted heated probe. 1.3 Objective/Purpose These measurements were taken to give information on water consumption by Picea mariana trees, the dominating tree species at SSA-OBS. In combination with the dimensional properties of the five measured trees (given in the information below) and the stand structural information, these data may be used to scale up water consumption by Picea mariana to a stand level for the time period 31-May-1994 until 27-September-1994. In combination with meteorological and soil water content information, these data may be used to 1) analyze the climatic and pedological control of water loss by Picea mariana trees on a short-term (diurnal) and long-term (seasonal) time scale and 2) calculate canopy conductance for water vapor exchange. These data may then be used for validation of results from gas exchange and soil-vegetation-atmosphere transform (SVAT)models for water and carbon exchange from trees. 1.4 Summary of Parameters and Variables Each line of the data file contains time and date information and xylem flux data taken at the same time for each of five trees. 1.5 Discussion Xylem sap flux density (XFD, unit: grams of H2O per square meter of hydroactive xylem per second = g m-2s-1) in the youngest, distal part of the hydroactive xylem was derived from continuous measurements of heat dissipation properties in the hydroactive xylem of tree boles at approximately 1.6 to 1.8 m height above the ground. A constant thermal energy input method with a point source heating device of 20 mm in length and a diameter of 2 mm (Granier, 1985) was used. The apparent temperature difference between the stem tissue and a heated probe (constant heat dissipation of the sensor: 200 mWatt) inserted in the outer xylem was monitored every 30 seconds, and a 30-minute mean was stored for each sensor. The sensor setup was covered with a radiation shield to avoid external radiative thermal load on the setup. The tree dimensions, diameter at breast height, height, and projected canopy area, were measured for the five trees . 1.6 Related Data Sets BOREAS RSS-17 Dielectric Constant Profile Measurements BOREAS RSS-17 Stem and Air Temperature Measurements BOREAS RSS-17 1994 ERS-1 Level-1 Backscatter Change Images 2. Investigators 2.1 Investigator(s) Name and Title Principal Investigator: Dr. JoBea Way Jet Propulsion Laboratory Co-Investigator: Dr. Kyle McDonald Jet Propulsion Laboratory Co-Investigator: Dr. Reiner Zimmermann Bayreuth Institute for Terrestrial Ecosystem Research (BITOEK) 2.2 Title of Investigation Monitoring Environmental and Phenologic State and Duration of State with SAR as Input to Improved C02 Flux Models 2.3 Contact Information Contact 1 --------- Dr. Reiner Zimmermann Bayreuth Institute for Terrestrial Ecosystem Research (BITOEK) Plant Ecology II University of Bayreuth GERMANY +49-921-555624 +49-921-555799 (fax) reiner.zimmermann@bitoek.uni-bayreuth.de Contact 2 --------- Dr. JoBea Way Jet Propulsion Laboratory California Institute of Technology Pasadena, CA USA (818) 354-8225 (818) 354-9476 (fax) way@lor.jpl.nasa. Contact 3 --------- Dr. Kyle McDonald Jet Propulsion Laboratory California Institute of Technology Pasadena, CA USA (818) 354-3263 (818) 354-9476 (fax) kyle.mcdonald@jpl.nasa.gov Contact 4 --------- Prof. Dr. Ram Oren Duke University Nicholas School of the Environment Durham, NC USA ramoren@duke.edu Contact 5 ------------- Jaime Nickeson Raytheon STX Corporation NASA GSFC Greenbelt, MD (301) 286-3373 (301) 286-0239 (fax) Jaime.Nickeson@gsfc.nasa.gov 3. Theory of Measurements Calculation of Xylem Flux with the Granier Method The following discussion depends to a large extent on Gülpen (1996) and Granier (1985): 3.1 General Principles of Measurement The constant current heating of a wire wrapped around the upper needle of the xylem sensor setup causes a constant warming of the wood around the needle. The constant electrical current applied to a constant electrical resistance causes a constant energy release. Combining the equation for Ohms law (1): U = R * I (1) U = Electrical voltage (Volts) R = Electrical resistance (Ohms) I = Electrical current (Amps) and the equation for electrical power (2): P = U * I (2) P = Electrical power (Watt) results in equation (3): P = R * I * I (3) The electrical resistance of the heated wire coil that is inserted into the wood is determined by the dimensions and electrical properties of the wire type. The sensors used were 20 mm in length; the electrical resistance of the heating coil is typically 10.2 Ohm. The constant current controller unit supplies the wire with 0.140 mAmpere. Thus, the energy release for this type of sensor can be calculated by using equation (3): P = 10.2 * 0.140 * 0.140 = 0.200 The total energy release of this sensor type is 200 mW at a length of 20 mm. This is 10 mW per mm of sensor length. The preference of constant current control over constant voltage control for the heating coil power supply has a practical reason: the variation of the electrical resistance in the connecting cables between the power supply and the heated sensor coil (caused by varying cable length, changes in environmental temperature conditions, direct radiation load from the Sun, or corrosion) does not affect the heating coil energy release when constant current is applied to the entire setup. The warming at the heated sensor needle is at its maximum if no water transport takes place. Thus, the temperature difference between the heated sensor and the reference sensor will be at its maximum at no flow conditions in the xylem. If xylem flux starts, the heated sensor will be cooled by the xylem water, which is at average stem temperature passing by the heated sensor. In this case, the measured temperature difference between the heated sensor and the reference sensor will decrease. The degree of cooling at the heated sensor is proportional to the intensity of xylem sap flow. This is the underlying principle of calculating the xylem sap flow with this sensor arrangement from a measured temperature difference between a heated sensor and a reference sensor. The formula obtained is based on a study by Granier (1985). For the calculation of the xylem flow, two parameters must be defined. The term XYLEM FLUX is a quantitative expression of xylem water passing through a single tree or through an entire stand of trees (=transpiration), while XYLEM FLUX DENSITY is the xylem flow related to an area through which the xylem sap is passing at a given point. The area is typically the cross-sectional area of hydroactive xylem in a tree stem. The xylem flux density (grams of H2O per square meter of hydroactive xylem per second = g m-2s-1) is the measured parameter obtained by using the Granier method in the data set included here. The xylem flux density measured can then be scaled up to a tree or stand level if the tree or whole stand cross-sectional areas of the trees are known. At this point of scaling up water flow in trees, it has to be taken into account that the xylem flux density varies with microclimatic conditions, tree water status, tree size, and xylem depth as well as tree species. For scaling up purposes, it is typically necessary to measure and analyze the above-mentioned parameters before the transpiration of trees and entire stands can be calculated. 3.2 Theory of Heat Exchange Between Heated Sensor and Xylem Tissue It is assumed that the energy that is produced by the heated sensor will be entirely transferred by the surrounding aluminum tube to the xylem tissue: h * S * (T-Tinf) = R * I * I (4) h = Heat exchange coefficient (W m-2 °C-1) S = Heat exchange surface (m2) T = Temperature of heated sensor (°C) Tinf = Temperature of unheated wood material (°C) R = Electric resistance (Ohm) I = Electric current (A) This means that the heat loss from the heated sensor to the wood depends on both: a) the contact surface between the heated sensor to the wood and b) the temperature difference between the heated sensor and the surrounding wood material. The contact surface area S remains a constant because it is given by the size of the sensor and by the surrounding aluminum tube. The exchange of heat energy between the heated sensor and the wood material, however, is determined by the heat exchange coefficient h. The heat exchange coefficient h can be calculated according to equation (5): h = R * I * I / S (T-Tinf) (5) At zero xylem sap flow condition, the temperature of the heated sensor is at its maximum. The heat exchange coefficient at zero xylem sap flow condition (hzero) can be calculated according to equation (3): hzero = R * I * I / S (Tmax-Tinf) (6) Tmax = Temperature of the heated sensor at zero xylem sap flow (maximum temperature measured at sensor). The actual heat exchange coefficient h changes with the onset of xylem sap flow: h = hzero ( 1 + alpha * ubeta ) (7) u = xylem flux density (mass of xylem water per area of hydroactive xylem in g m-2 s-1) hzero = Heat exchange coefficient at u = 0 (zero xylem flow) The variables alpha and beta are empirically measured calibration factors for a material (in this example, xylem woody tissue) that describe at a given xylem flow density the change of the relationship of the actual heat exchange coefficient, h, at any given xylem flow to the heat exchange coefficient at zero flow, hzero. For the calculation of the xylem flux density, u, the equation (7) can be rearranged: u = ( 1/ alpha * (h - hzero) / hzero )(1/beta) (8) Integration of equations (5) and (6) into equation (8) results in: u = ( 1 / alpha * (Tmax-Tinf)-(T-Tinf) / (T-Tinf) )(1/beta) (9) This means: u = ( 1 / alpha * (Tmax - T) / (T-Tinf) )(1/beta) (10) Within equation (10) the term (11) is a measure of the degree of cooling of the heated sensor. The term is also proportional to the xylem sap flux. (Tmax-T) / (T-Tinf) (11) Granier (1985) calls this term (11) the "flow index, K." The Granier sensor method does not measure absolute temperatures at the heated or the reference sensor. Rather, it measures the temperature difference between both sensors. Technically, this temperature difference is measured by a pair of copper- constantane thermocouples that are connected at the constantane ends. The inverted thermocouple array produces a predictable voltage output at the two copper ends when both thermocouple junctions are exposed to different temperatures. For copper-constantane thermocouples the voltage output increases at approximately 40 microvolts per degree Celsius within ambient temperatures for plant life. For the temperature difference measurements, the equations (12) and (13) are valid: Tmax = Tdeltamax + Tinf (12) T = Tdeltaactual + Tinf (13) Tdeltamax = Temperature difference at u = 0 (zero xylem flow) when the probe temperature is at its maximum temperature elevation above ambient material (wood) temperature. Tdeltaactual = Actual measured temperature difference From this, the flux index K according to Granier (1985) can be calculated: (Tdeltamax + Tinf) - (Tdeltaactual + Tinf) K = ------------------------------------------------- (14) (Tdeltaactual + Tinf) - Tinf This can be rearranged as: K = ( Tdeltamax - Tdeltaactual ) / Tdeltaactual (15) The derivation of a flux index K from the theoretical consideration of heat exchange between an inserted and actively heated xylem flux probe and the surrounding xylem tissue demonstrates the characteristics of the xylem flux measurement method according to Granier (1985): ? The measurement of xylem flow is achieved by calculation of the xylem flux density u, which is proportional to the flux index K. ? The flux index K is calculated by using the factors alpha and beta. These two factors can be empirically derived by experiments for woody xylem tissue. The factors are independent of the ambient temperature conditions. 3.3 Determination of the Calibration Factors Alpha and Beta Because the flux index K is proportional to the xylem flux density u (equation (10)), the following relationship exists: K = alpha * ubeta (16) The variation of the flux index K was experimentally investigated for obtaining a calibration for his system. Because of large anatomical differences, the calibration factors were determined for various xylem types and tree species by Granier (1985). Data were obtained for Pseudotsuga menziesii, Pinus nigra and Quercus pedunculata, and Picea abies (Granier 1985), and for Quercus robur, Malus domestica, and Castanea sativa (Lu 1992). The aim of these studies was to obtain a relationship between K and the gravimetrically measured xylem flux density in order to be able to calculate the factors alpha and beta. The experiments were performed using stem segments through which water was percolated by applying various hydrostatic pressures. The xylem flow was measured gravimetrically, and the xylem flux density was recalculated from the xylem flow. The xylem flux density was then compared with the measured flux index K. The relationship between K and u was determined by a linear regression model that delivered the factors alpha and beta. It was found that all tree species studied showed the same relationship between u and K. The regression model had a r2 of 0.92 and a replication of n = 53 samples (Granier 1985). Further studies supported the general validity of this model (Granier, 1989; Lu, 1992). From these experiments, the following relationship between K and u (g * m-2 * s- 1) was derived: K = 0.0206 u0.8124 (16a) For u (g * m-2 * s-1), the following equation is obtained: u = 118.99 * K1.234 (17) This is the general form of the equation used for calculation of xylem flux density when the flux index K is measured with the Granier method. 3.4 Calculation of Tree and Stand Transpiration The xylem flux density is related to the xylem flow (transpiration) of a whole stem or an entire stand of trees as follows: u = F / SA (18) u = xylem flux density (g m-2 s-1) F = xylem flow (transpiration) (g s-1) SA = hydroactive sapwood cross sectional area (m2) Equation (16) is valid if the hydroactive xylem depth is equal to or larger than the sensor insertion depth. If the hydroactive xylem depth is smaller than the sensor depth (e.g., with most ring porous trees), the flux density must be corrected to its actual and higher value. The xylem flow for a tree or an entire stand can be calculated from the knowledge of the xylem flux density u and the total hydroactive sapwood area of the tree or the forest stand. This assumption implies that no xylem flux density variations exist with tree dimensions, canopy structure, and xylem depth. F = u * SA (19) 4. Equipment 4.1 Sensor/Instrument Description Technically, the heated sensor consists of two units: 1) A Teflon-insulated constantane wire with a known electrical resistance that is wrapped around a steel syringe. The wire releases a constant amount of heat energy. The external size of the sensor is a 2-mm diameter, 20-mm length of inserted heating coil. 2) A thermocouple of a pair of copper and constantane wires connected together at its tip. The tip is at the center of the sensor setup inside the steel syringe. The thermocouple measures the temperature of the sensor and is electrically insulated from the heated wire and the steel syringe. An external direct current power supply with a controller for constant current output is connected to the heating wire coil. The heated wire has a known and constant electrical resistance. Furthermore, a constantane wire, a nickel- copper alloy, does not change its electrical resistance at varying temperatures as regular metal wires typically do. 4.1.1 Collection Environment Data were collected from May 1994 until September 1994. Air temperature was typically above 0 °C, and conditions varied widely diurnally from cool and clear to overcast and rain. 4.1.2 Source/Platform Black spruce trees. 4.1.3 Source/Platform Mission Objectives This study was undertaken to obtain water flux information from the tree canopy in order to allow validation of water exchange models. 4.1.4 Key Variables Xylem flux density (XFD) in grams of water/square meter of hydroactive xylem/second) 4.1.5 Principles of Operation Continuous thermal measurement with constant power input. 4.1.6 Sensor/Instrument Measurement Geometry Insertion depth of sensors was horizontal and central with a depth of 20 mm into the outer ring of the hydroactive xylem from the cambium layer on. 4.1.7 Manufacturer of Sensor/Instrument Custom made by: B. Stumpf Technical Precision Instruments Trebgest, Germany 4.2 Calibration No field calibration of the sensors is necessary. Constant current power supply of sensors was checked during installation and removal of the sensors. All constant current source controllers were stable during operation and varied within less than 1% of 140 mAmp. 4.2.1 Specifications Sensors were running on 140 mAmp at 10.204-Ohm heating wire resistance. Energy release over 20 mm in sensor length was thus 200 mAmp. Thermocouple wires used are copper-constantane. Two thermocouples were connected copper-constantane-copper and given 40 µVolt per 1° C of temperature difference measured at the two joints at 20° C ambient temperature. 4.2.1.1 Tolerance Measurement depends on the accuracy of thermocouple measurements and natural temperature gradients in the measured stem. 4.2.2 Frequency of Calibration Not applicable. 4.2.3 Other Calibration Information Not applicable. 5. Data Acquisition Methods Temperature difference from the xylem flux sensors was automatically logged on a data logger (DL-2 with LAC-1) in double ended mode, autoranging on (Delta-T Devices, England). Data were downloaded on a PC laptop and processed using Dataman (Ce Huang, Duke University, USA), Sigmaplot 4.0 (Jandel Inc. USA), SPSS (USA), and Excel 4.0 (Microsoft, USA). 6. Observations All sensors worked without problems for the entire time period of observation. 6.1 Data Notes There was a period from July 16 through July 27 when the data were reported every 10 minutes instead of every half hour. 6.2 Field Notes None given. 7. Data Description The five trees measured had the following dimensional properties: -------------------------------------------------------- Tree# = Tree number DBH = Stem diameter at breast height including bark (mm) TH = Tree height (m) PCA = Projected canopy area (m2) -------------------------------------------------------- Tree# , DBH , TH , PCA Tree1 , 138 , 10.0 , 2.12 Tree2 , 90 , 6.5 , 2.00 Tree3 , 99 , 8.2 , 1.22 Tree4 , 45 , 6.9 , 0.57 Tree5 , 180 , 12.7 , 5.30 7.1 Spatial Characteristics 7.1.1 Spatial Coverage The measurement site was located at the SSA OBS flux tower site, approximately 20 meters northeast of the tower. The North American Datum 1983 (NAD83) coordinates of the SSA-OBS flux tower are given below: -------------------------------------------------------------------------- UTM UTM UTM Site Id Grid Id Longitude Latitude Easting Northing Zone -------------------------------------------------------------------------- SSA-OBS-XYL01 G8I4T 105.11779W 53.98717N 492276.5 5982100.5 13 7.1.2 Spatial Coverage Map Not available. 7.1.3 Spatial Resolution The spatial resolution of a given measurement is one tree. 7.1.4 Projection Not applicable. 7.1.5 Grid Description Not applicable. 7.2 Temporal Characteristics 7.2.1 Temporal Coverage Data collection took place continuously from 31-May-1994 to 27-September-1994 7.2.2 Temporal Coverage Map Not applicable. 7.2.3 Temporal Resolution Sap flux was measured every 1 minute and averaged into 30 minute ensembles. The 30-minute ensembles are presented. There was a period from July 17 through July 27 when the fluxes were reported every 10 minutes instead of every thirty. 7.3 Data Characteristics Data characteristics are defined in the companion data definition file (rss17xyf.def). 7.4 Sample Data Record Sample data format shown in the companion data definition file (rss17xyf.def). 8. Data Organization 8.1 Data Granularity All of the Xylem Flux Density Measurements at the SSA-OBS Site 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 within single apostrophe marks. There are no spaces between the fields. Sample data records are shown in the companion data definition file (rss17xyf.def). 9. Data Manipulations 9.1 Formulae Data of xylem flux density do not need further processing. 9.1.1 Derivation Techniques and Algorithms See Section 3. 9.2 Data Processing Sequence 9.2.1 Processing Steps See Section 5. 9.2.2 Processing Changes None. 9.3 Calculations 9.3.1 Special Corrections/Adjustments Not applicable. 9.3.2 Calculated Variables See Section 3. 9.4 Graphs and Plots None. 10. Errors 10.1 Sources of Error Human errors while staring into the tube and passing out and hitting the keyboard. 10.2 Quality Assessment 10.2.1 Data Validation by Source The data were checked for consistency and outliers 10.2.2 Confidence Level/Accuracy Judgment Good. 10.2.3 Measurement Error for Parameters None given. 10.2.4 Additional Quality Assessments We provided only those data which were of good quality. Faulty data and data acquired during time periods for which our measurement technique was not robust (e.g. data acquired during periods when the tree was frozen or undergoing freeze/thaw transitions) were not included in the supplied data set. 10.2.5 Data Verification by Data Center BORIS Staff reviewed the data files during the data base loading process. 11. Notes 11.1 Limitations of the Data None. 11.2 Known Problems with the Data None, as long as no frost condition in the tree bole occurs. Data from periods of frost in the tree boles are not presented. 11.3 Usage Guidance None given. 11.4 Other Relevant Information None given. 12. Application of the Data Set These measurements were taken to give information on water consumption by Picea mariana (black spruce) trees, the dominating tree species at SSA-OBS. In combination with the dimensional properties of the five measured trees (given in Section 7.1) and the stand structural information, these data may be used to scale up water consumption by Picea mariana to a stand level for the time period from 31-May-1994 until 27-September-1994. In combination with meteorological and soil water content information, these data may be used to: 1) Analyze the climatic and pedological control of water loss by Picea mariana trees on a short-term (diurnal) and long-term (seasonal) time scale. 2) Calculate canopy conductance for water vapor exchange. These data may then be used for validation of results from gas exchange models for water and carbon exchange from trees. 13. Future Modifications and Plans No modifications are planned. 14. Software Data were downloaded on a PC laptop and processed using Dataman (Ce Huang, Duke University, USA), Sigmaplot 4.0 (Jandel Inc. USA), SPSS (USA), and Excel 4.0 (Microsoft, USA). 14.1 Software Description Data collection and transformation from binary data to ASCII data were performed in the field with software from Delta-T, Cambridge, UK. Processing of the data was performed by Reiner Zimmermann with custom software Dataman written by Huang Ce for a PC-DOS computer in TURBOBASIC at Duke University, North Carolina, USA. Data transformation, data check, and data visualization were done with customized program routines for SIGMAPLOT 4.0 (Jandel Scientific) for DOS by Reiner Zimmermann at BITOEK, Bayreuth, Germany. 14.2 Software Access Dataman is available upon request from Huang Ce, Nicholas School of the Environment, Duke University, North Carolina, USA. 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 RSS-17 xylem flux density 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 Oak Ridge, TN (423) 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 as tabular ASCII files. 17. References 17.1 Platform/Sensor/Instrument/Data Processing Documentation None. 17.2 Journal Articles and Study Reports Granier, A. 1985. Une nouvelle methode pour la mesure du flux de seve brute dans le tronc des arbres. Ann. Sci. For. 42 (2) 81-88. Granier, A. 1987. Evaluation of Transpiration in a Douglas-fir Stand by means of Sap Flow Measurements. Tree Physiology. Vol. 3, pp. 309-319. Granier, A., R. Huc, and F. Colin. 1992. Transpiration and stomatal conductance of two rain forest species growing in plantations (Simarouba amara and Goupia glabra) in French Guyana. Ann. Sci. For. 49, 17-24. Gülpen, M. 1996. Xylemfluss, Elementtransport und Bindung von Calcium und Magnesium in Fichten (Picea abies (L.) Karst.) von den ARINUS- Versuchsflächen im Schwarzwald. Freiburg. Bodenk. Abh. 36, Freiburg, Germany, 163 pp. Hogg, E. H., T. A. Black, G. den Hartog, H. H. Neumann, R. Zimmerman, P. A. Hurdle, P. D. Blanken, Z. Nesic, P. C. Yang, R. M. Staebler, K. McDonald, and R. Oren. 1997. A Comparison of Sap Flow and Fluxes of Water Vapour from a Boreal deciduous forest. Journal of Geophysical Research (JGR), BOREAS Special Issue, 102(D24), Dec. 1997, pp. 28929-28937. Lu, P. 1992. Ecophysiologie et reaction a la secheresse de trois espeches de coniferes (Abies alba Miller, Picea abies (L.) Karsten et Pinus sylvestris L.); effet de l age. Dissertation, University of Nancy, France, 116 pp. 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 early results 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 (OPS DOC 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 (OPS DOC 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. (1997). "BOREAS in 1997: Experiment Overview, Scientific Results and Future Directions", Journal of Geophysical Research (JGR), BOREAS Special Issue, 102(D24), Dec. 1997, pp. 28731-28770. Way, J.B., R. Zimmermann, E. Rignot, K. McDonald, and R. Oren. Winter and spring thaw as observed with imaging radar at BOREAS. Journal of Geophysical Research (JGR), BOREAS Special Issue, 102(D24), Dec. 1997, pp. 29673-29684. 17.3 Archive/DBMS Usage Documentation None. 18. Glossary of terms None. 19. List of acronyms ASCII - American Standard Code for Information Interchange BOREAS - BOReal Ecosystem-Atmosphere Study BORIS - BOREAS Information System DAAC - Distributed Active Archive Center EOS - Earth Observing System EOSDIS - EOS Data and Information System GSFC - Goddard Space Flight Center NASA - National Aeronautics and Space Administration NSA - Northern Study Area OBS - Old Black Spruce ORNL - Oak Ridge National Laboratory PANP - Prince Albert National Park PDP - Portable Dielectric Probe RSS - Remote Sensing Science SSA - Southern Study Area SVAT - Soil-Vegetation-Atmosphere Transfer URL - Uniform Resource Locator (a World Wide Web address) UTM - Universal Transverse Mercator 20. Document Information 20.1 Document Revision Date(s) Written: 01-Jun-1997 Last Updated: 14-Sep-1998 20.2 Document Review Date(s) BORIS Review: 10-Sep-1997 Science Review: 11-Jul-1998 20.3 Document ID 20.4 Citation Please acknowledge the efforts of the following investigators when using this dataset: R. Zimmermann, K. C. McDonald, J. B. Way and R. Oren 20.5 Document Curator 20.6 Document URL Keywords: Xylem flux density Water consumption Transpiration Picea mariana Black spruce RSS17_Xylem_Flux.doc 09/14/98