Open AccessA comparison of sap flow and eddy fluxes of water vapor from a boreal deciduous forest
Author(s) -
Hogg Edward H.,
Black T. Andrew,
den Hartog Gerry,
Neumann Harold H.,
Zimmermann Reiner,
Hurdle Patrick A.,
Blanken Peter D.,
Nesic Zoran,
Yang Paul C.,
Staebler Ralf M.,
McDonald Kyle C.,
Oren Ram
Publication year - 1997
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/96jd03881
Subject(s) - transpiration , eddy covariance , canopy , environmental science , vapour pressure deficit , canopy conductance , atmospheric sciences , deciduous , flux (metallurgy) , stomatal conductance , water vapor , bowen ratio , atmosphere (unit) , hydrology (agriculture) , sensible heat , botany , ecology , chemistry , ecosystem , geography , meteorology , geology , biology , photosynthesis , organic chemistry , geotechnical engineering
Water flux to the atmosphere was measured from a mature stand of aspen ( Populus tremuloides Michx.) in Saskatchewan, Canada, as part of the Boreal Ecosystem‐Atmosphere Study (BOREAS). Diurnal and seasonal changes in transpiration were monitored using two sap flow techniques and were compared against the difference between eddy correlation measurements of water vapor flux made above and below the aspen canopy. The three methods showed similar diurnal and seasonal trends in water flux, although sap flow lagged the eddy correlation measurements by about 1 hour diurnally due to changes in water storage within the trees. During the growing season, all methods showed a linear increase in midday transpiration with above‐canopy vapor pressure deficit (VPD) up to ∼1 kPa, beyond which transpiration was relatively constant (VPD 1–2.5 kPa). A similar relationship was obtained when total daily transpiration was plotted against mean daytime VPD. The results are consistent with other observations that stomatal conductance of the aspen canopy decreases at high VPD. The complementary benefits of simultaneous monitoring of canopy transpiration by both eddy correlation and sap flow measurements are discussed.