The Dynamics of Transpiration to Evapotranspiration Ratio under Wet and Dry Canopy Conditions in a Humid Boreal Forest

• Published in: Forests
• Main Authors: Bram Hadiwijaya, Steeve Pepin, Pierre-Erik Isabelle, Daniel F. Nadeau
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2020
• Subjects: boreal forest; eddy-covariance; evapotranspiration; sap flow; transpiration; leaf wetness; interception; Plant ecology; QK900-989; Canada; Subarctic
• Online Access: https://doi.org/10.3390/f11020237; https://doaj.org/article/8a7cbc63a2b14ac988ed072d7e9e43a9

Humid boreal forests are unique environments characterized by a cold climate, abundant precipitation, and high evapotranspiration. Transpiration ( <math display="inline"> <semantics> <msub> <mi>E</mi> <mi>T</mi> </msub> </semantics> </math> ), 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 ( <math display="inline"> <semantics> <mrow> <msub> <mi>E</mi> <mi>T</mi> </msub> <mo>/</mo> <mi>E</mi> </mrow> </semantics> </math> ) under transient canopy wetness states. This study presents field measurements of <math display="inline"> <semantics> <mrow> <msub> <mi>E</mi> <mi>T</mi> </msub> <mo>/</mo> <mi>E</mi> </mrow> </semantics> </math> at the Montmorency Forest, Québec, Canada: a balsam fir boreal forest that receives <math display="inline"> <semantics> <mrow> <mo>∼</mo> <mn>1600</mn> </mrow> </semantics> </math> mm of precipitation annually (continental subarctic climate; Köppen classification subtype Dfc). Half-hourly observations of E and <math display="inline"> <semantics> <msub> <mi>E</mi> <mi>T</mi> </msub> </semantics> </math> 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 <math display="inline"> <semantics> <mrow> <mn>34</mn> <mo>%</mo> <mo>±</mo> ...