HR: 0800h
AN: H51H-0880    [Abstracts]
TI: A New Technique for Up-scaling Sap Flow Transpiration Measurements to Stand or Landscape Scale Fluxes
AU: * Miller, G R
EM: gmiller@berkeley.edu
AF: Civil and Environmental Engineering, University of California - Berkeley, 760 Davis Hall, Berkeley, CA 94720-1710, United States
AU: Chen, X
EM: chenxy@berkeley.edu
AF: Civil and Environmental Engineering, University of California - Berkeley, 760 Davis Hall, Berkeley, CA 94720-1710, United States
AU: Rubin, Y
EM: rubin@ce.berkeley.edu
AF: Civil and Environmental Engineering, University of California - Berkeley, 760 Davis Hall, Berkeley, CA 94720-1710, United States
AU: Baldocchi, D
EM: baldocchi@nature.berkeley.edu
AF: Environmental Science, Policy, and Management, University of California - Berkeley, Berkeley, CA 94720-3100, United States
AB: Measurements of individual tree transpiration, obtained using the sap flow technique, are easier to collect and less expensive than other traditional measurements of ecosystem evapotranspiration, such as eddy-covariance and lysimetery. Up-scaling these point measurements to a stand or a landscape level, however, is a challenge, especially in water-controlled ecosystems. At these scales, sap flow cannot be treated solely as a function of diameter; available soil moisture strongly influences transpiration, and this can vary considerably across a landscape. In this study, geostatistical and partitional clustering methods were used to locate a network of sap flow and soil moisture sensors across a California Oak Savanna. Eight "representative trees" were monitored; each was systematically selected to represent a subgroup of the population within a 200 x 200 m plot. All trees in a subgroup had similar diameters and soil moisture status and were presumed to have correspondingly similar sap flow. The sensors collected half-hour data over the course of the 2007 growing season, during which unusually low rainfall occurred. The sap flow data for each tree were transformed into specific water flux, and a total stand level water flux was computed at hourly and daily time-steps. Large diameter trees in wet areas typically contributed to almost 40% of the total stand flux, while they accounted for less than 10% of the total population. To test the method, these fluxes were then compared to the measurements of stand level tree transpiration collected using the eddy- covariance towers on site. In the future, this technique could be used to measure transpiration of targeted trees over a broader area or in terrain or situations where eddy-covariance is not feasible.
DE: 1813 Eco-hydrology
DE: 1818 Evapotranspiration
DE: 1843 Land/atmosphere interactions (1218, 1631, 3322)
DE: 1852 Plant uptake
DE: 1895 Instruments and techniques: monitoring
SC: Hydrology [H]
MN: 2007 Fall Meeting