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http://dx.doi.org/10.5532/KJAFM.2009.11.4.233

Understory Evapotranspiration Measured by Eddy-Covariance in Gwangneung Deciduous and Coniferous Forests  

Kang, Min-Seok (Global Environment Laboratory & Department of Atmospheric Sciences, Yonsei University)
Kwon, Hyo-Jung (Global Environment Laboratory & Department of Atmospheric Sciences, Yonsei University)
Lim, Jong-Hwan (Division of Forest Conservation, Korea Forest Research Institute)
Kim, Joon (Global Environment Laboratory & Department of Atmospheric Sciences, Yonsei University)
Publication Information
Korean Journal of Agricultural and Forest Meteorology / v.11, no.4, 2009 , pp. 233-246 More about this Journal
Abstract
The partitioning of evapotranspiration (ET) into evaporation (E) and transpiration (T) is critical in understanding the water cycle and the couplings between the cycles of energy, water, and carbon. In forests, the total ET measured above the canopy consists of T from both overstory and understory vegetation, and E from soil and the intercepted precipitation. To quantify their relative contributions, we have measured ET from the floors of deciduous and coniferous forests in Gwangneung using eddy covariance technique from 1 June 2008 to 31 May 2009. Due to smaller eddies that contribute to turbulent transfer near the ground, we performed a spectrum analysis and found that the errors associated with sensor separation were <10%. The annual sum of the understory ET was 59 mm (16% of total ET) in the deciduous forest and 43 mm (~7%) in the coniferous forest. Overall, the understory ET was not negligible except during the summer season when the plant area index was near its maximum. In both forest canopies, the decoupling factor ($\Omega$) was about ~0.15, indicating that the understory ET was controlled mainly by vapor pressure deficit and soil moisture content. The differences in the understory ET between the two forest canopies were due to different environmental conditions within the canopies, particularly the contrasting air humidity and soil water content. The non-negligible understory ET in the Gwangneung forests suggests that the dual source or multi-level models are required for the interpretation and modeling of surface exchange of mass and energy in these forests.
Keywords
Evapotranspiration; Understory; Eddy-Covariance; Decoupling factor; Coniferous forest; Deciduous forest;
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