Journal Article

Transpiration of a boreal pine forest measured by branch bag, sap flow and micrometeorological methods

B. Saugier, A. Granier, J. Y. Pontailler, E. Dufrêne and D. D. Baldocchi

in Tree Physiology

Volume 17, issue 8-9, pages 511-519
Published in print August 1997 | ISSN: 0829-318X
Published online August 1997 | e-ISSN: 1758-4469 | DOI: http://dx.doi.org/10.1093/treephys/17.8-9.511
Transpiration of a boreal pine forest measured by branch bag, sap flow and micrometeorological methods

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Three independent methods were used to evaluate transpiration of a boreal forest: the branch bag, sap flow and eddy covariance methods. The branch bag method encloses several thousand needles and gives a continuous record of branch transpiration. The sap flow method provides a continuous record of sap velocity and an estimate of tree transpiration. The eddy covariance method typically measures evaporation rates between a forest and the atmosphere. We deployed an extra eddy covariance system below the forest to estimate canopy transpiration by difference.

The three systems detected small water vapor fluxes despite a plentiful supply of energy to drive evaporation. We also observed that transpiration rates were low even when the soil was well supplied with water. Low rates of transpiration were attributed to the canopy's low leaf area index and the marked reduction in stomatal conductance as vapor pressure deficits increased. Water vapor fluxes, derived from the sap flow method, lagged behind those derived by the branch bag method by 1 to 2 h. The sap flow method also suffered from sampling errors caused by the non-uniformity of flow across the sapwood and the spatial variability of sapwood cross section throughout the forest. Despite technical difficulties associated with hourly measurements, daily totals of transpiration agreed well with values derived from micrometeorological systems.

Keywords: canopy transpiration; eddy covariance method; jack pine; Pinus banksiana; transpiration rate; water loss; water vapor flux

Journal Article.  0 words. 

Subjects: Plant Sciences and Forestry

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