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The Dynamics of Transpiration to Evapotranspiration Ratio under Wet and Dry Canopy Conditions in a Humid Boreal Forest
Humid boreal forests are unique environments characterized by a cold climate, abundant precipitation, and high evapotranspiration. Transpiration ( ), as a component of evapotranspiration (E), behaves differently under wet and dry canopy conditions, yet very few studies have focused on the dynamics of transpiration to evapotranspiration ratio ( ) under transient canopy wetness states. This study presents field measurements of at the Montmorency Forest, Québec, Canada: a balsam fir boreal forest that receives mm of precipitation annually (continental subarctic climate; Köppen classification subtype Dfc). Half-hourly observations of E and were obtained over two growing seasons using eddy-covariance and sap flow (Granier’s constant thermal dissipation) methods, respectively, under wet and dry canopy conditions. A series of calibration experiments were performed for sap flow, resulting in species-specific calibration coefficients that increased estimates of sap flux density by , compared to Granier’s original coefficients. The uncertainties associated with the scaling of sap flow measurements to stand , especially circumferential and spatial variations, were also quantified. From 30 wetting−drying events recorded during the measurement period in summer 2018, variations in were analyzed under different stages of canopy wetness. A combination of low evaporative demand and the presence of water on the canopy from the rainfall led to small . During two growing seasons, the average ranged from to . The change in total precipitation was not the main driver of seasonal variation, therefore it is important to analyze the impact of rainfall at half-hourly intervals.
The Dynamics of Transpiration to Evapotranspiration Ratio under Wet and Dry Canopy Conditions in a Humid Boreal Forest
Humid boreal forests are unique environments characterized by a cold climate, abundant precipitation, and high evapotranspiration. Transpiration ( ), as a component of evapotranspiration (E), behaves differently under wet and dry canopy conditions, yet very few studies have focused on the dynamics of transpiration to evapotranspiration ratio ( ) under transient canopy wetness states. This study presents field measurements of at the Montmorency Forest, Québec, Canada: a balsam fir boreal forest that receives mm of precipitation annually (continental subarctic climate; Köppen classification subtype Dfc). Half-hourly observations of E and were obtained over two growing seasons using eddy-covariance and sap flow (Granier’s constant thermal dissipation) methods, respectively, under wet and dry canopy conditions. A series of calibration experiments were performed for sap flow, resulting in species-specific calibration coefficients that increased estimates of sap flux density by , compared to Granier’s original coefficients. The uncertainties associated with the scaling of sap flow measurements to stand , especially circumferential and spatial variations, were also quantified. From 30 wetting−drying events recorded during the measurement period in summer 2018, variations in were analyzed under different stages of canopy wetness. A combination of low evaporative demand and the presence of water on the canopy from the rainfall led to small . During two growing seasons, the average ranged from to . The change in total precipitation was not the main driver of seasonal variation, therefore it is important to analyze the impact of rainfall at half-hourly intervals.
The Dynamics of Transpiration to Evapotranspiration Ratio under Wet and Dry Canopy Conditions in a Humid Boreal Forest
Bram Hadiwijaya (author) / Steeve Pepin (author) / Pierre-Erik Isabelle (author) / Daniel F. Nadeau (author)
2020
Article (Journal)
Electronic Resource
Unknown
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