Forest Water Use Data 2000

from the Walker Branch Throughfall Displacement Experiment (TDE)

1.1 Document Title: TDE forest water use data
1.2 Revision Date:  April 10, 2003
1.3 Document Summary:  Forest water use observations collected during the 2000 growing season.
1.4 Sponsor: Office of Science,  Biological and Environmental Research, U. S. DOE

2.1 Investigator and data set contact:

Stan D. Wullschleger (
 Senior Research Staff Member
 Environmental Sciences Division
 Oak Ridge National Laboratory
 Bethel Valley Road
 P.O. Box 2008
 Oak Ridge, TN 37831-6422
2.2 Title of Investigation:
Walker Branch Throughfall Displacement Experiment (TDE)

Hourly estimated forest water use for the ambient, wet, and dry TDE treatment sites.


Forest water use was estimated as the product of measured sap velocity, cross-sectional sapwood area for the stand, and the fraction of sapwood functional in water transport (Wullschleger et al. 2000).  Thermal dissipation probes (Model TDP-30, Dynamax, Inc., Houston, TX) were used to estimate rates of sap velocity for eight trees of multiple species on each of the three TDE plots.  These probes consist of two probes that are inserted into the sapwood (Granier 1987).  The upper probe was installed at a height of 1.3 m and contained a heating element, whereas the lower probe served as an unheated reference.  Each probe contained a thermocouple and the temperature difference between the probes was used to calculate rates of sap velocity.  Species-specific allometric equations were developed for estimating sapwood area from measured tree diameters.  Diameter and sapwood thickness were measured on trees growing in closed-canopy stands on Walker Branch Watershed.  Stem diameter was measured with a diameter tape, whereas sapwood and bark thickness were measured with a digital caliper.  Heat-pulse probes (Greenspan Technology Pty. Ltd., Warwick, Queensland, Australia) were used to estimate the fraction of sapwood functional in water transport for overstory species on the TDE.  Each probe consisted of two thermistors, one 10 mm upstream and the other 5 mm downstream from a central heater, and probes were implanted to each of four pre-determined depths in the sapwood (Wullschleger and King 2000).  Insertion depths were calculated so that thermistors were optimally located within concentric annuli of equal sapwood area.  An increment bore was used to extract a sample of sapwood near where the probes were implanted for determination of wood density and water content.  The fraction of sapwood functional in water transport (a value between 0 and 1) was calculated for each measurement tree (Wullschleger et al. 2003).  Forest water use is expressed in units of mm per hour and refers to water use on a ground area basis weighted for species composition (Wullschleger et al. 2001).  Estimates include contributions from both over-story and under-story species (Wullschleger et al. 1998).


Sap velocity was measured hourly during the growing season of 2000 for the purpose of estimating forest water use for the three TDE plots.  Measurements were made on dominant species of the forest over-story, as well as smaller stature individuals in the under-story.  From these data, seasonal patterns of water use for the stand as influenced by canopy leaf area development, environmental variables, and soil water content were examined.


Data are provided in comma delimited csv files where the first line includes the variable names and subsequent lines include the following data by day of year.

6.1 Variable, Definition, and Units

6.2 Number of Records: 4824 measurements for each TDE plot

6.3 Missing data:

6.4 Related Data Sets:



8.1 Limitations of the data
Measurements of sap velocity using thermal dissipation probes are routinely used to assess rates of sap flow for trees and integration of such data for quantifying water use for forest stands.  However, we have observed that, for unknown reasons, the sap flow technique provides an under-estimate of water use compared to eddy covariance measurements made on similar forest stands elsewhere on the Walker Branch Watershed (Wilson et al. 2001).

8.2 Known Problems With The Data

8.3 Usage Guidance


Granier A (1987) Evaluation of transpiration in a Douglas-fir stand by means of sap flow measurements.  Tree Physiol 3:309-320.

Wilson KB, Hanson PJ, Mulholland PJ, Baldocchi DD, Wullschleger SD (2001) A comparison of methods for determining forest evapotranspiration and its components across scales: sap-flow, soil water budget, eddy covariance, and catchment water balance. Agric For Meteor 106:153-168,

Wullschleger SD, Hanson PJ, Tschaplinski TJ (1998) Whole-plant water flux in understory red maple exposed to altered precipitation regimes.  Tree Physiol 18:71-79.

Wullschleger SD, King AW (2000) Radial variation in sap velocity as a function of stem diameter and sapwood thickness in yellow-poplar trees.  Tree Physiol 20:511-518.

Wullschleger SD, Wilson KB, Hanson PJ (2000) Environmental control of whole-plant transpiration, canopy conductance and estimates of the decoupling coefficient for large red maple trees.  Agric For Meteorol 104:157-168.

Wullschleger SD, Hanson PJ, Todd DE (2001) Transpiration from a multi-species deciduous forest as estimated by xylem sap flow techniques.  For Ecol Manag 143:205-213.

Wullschleger SD, Hanson PJ, Todd DE (2003) Forest water use as influenced by precipitation change. Chapter 21 in Hanson PJ, Wullschleger SD (Eds), North American Temperate Deciduous Forest Responses to Changing Precipitation Regimes, Springer, New York, pp 363-377.

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