Effects of soil moisture and vapor pressure deficit on evapotranspiration in a hinoki [Chamaecyparis obtusa] plantation
1993
Hattori, S. (Forestry and Forest Products Research Inst., Kyoto (Japan). Kansai Branch) | Tamai, K. | Abe, T.
Evapotranspiration in the growing season was measured using a micrometeorological approach in a hinoki (Chamaecyparis obtusa S. et Z.) stand, and the effects of soil moisture and vapor pressure deficit (v.p.d.) on it were analyzed. The critical soil moisture (c.s.m.) at which transpiration began to decline was estimated as pF 2.45, and as the soil layer dried out over a range of c.s.m., the evapotranspiration decreased exponentially due to the limitation of extractable water. The limitation of evapotranspiration, which might be caused by closing stomata, was found in such a condition that the v.p.d. surpassed 10 mb during the daytime in spite of no shortage of soil moisture. As a result, the daytime trend of evapotranspiration appeared to be controlled by a combination of soil moisture content and v.p.d. Aerodynamic parameters, such as zero plane displacement (d) and roughness length (zo), showed changes depending upon wind speed. As a whole, d decreased, and zo increased associated with increasing wind speed. Canopy resistance stayed almost constant ranging between 0.5 sec/m and 1.0 sec/m during daytime and increasing toward late afternoon in wet soil conditions. When the soil layer dried out from over the c.s.m., canopy resistance became larger by several times than that below the c.s.m
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