Transpiration and canopy conductance in a pristine broad-leaved forest of Nothofagus: an analysis of xylem sap flow and eddy correlation measurements

Tree transpiration was determined by xylem sap flow and eddy correlation measurements in a temperate broad-leaved forest of Nothofagus in New Zealand (tree height: up to 36 m, one-sided leaf area index: 7). Measurements were carried out on a plot which had similar stem circumference and basal area p...

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Bibliographic Details
Published in:	Oecologia Vol. 91; no. 3; pp. 350 - 359
Main Authors:	Kostner, B.M.M, Schulze, E.D, Kelliher, F.M, Hollinger, D.Y, Byers, J.N, Hunt, J.E, McSeveny, T.M, Meserth, R, Weir, P.L
Format:	Journal Article
Language:	English
Published:	Berlin Springer-Verlag 01-09-1992 Springer
Subjects:	Animal and plant ecology Animal, plant and microbial ecology Biological and medical sciences canopy Coniferous forests Flux density Forest canopy Fundamental and applied biological sciences. Psychology Nothofagus Nothofagus fusca Nothofagus menziesii Sap Sap flow Sapwood Synecology Terrestrial ecosystems Transpiration Tree crowns Trees Xylem New Zealand Oceania Nothofagus menziesii Sap Xylem Stomatal conductance Environmental factor Canopy (vegetation) Evaporation Fagaceae Transpiration Dicotyledones Angiospermae Humidity Hardwood forest tree Spermatophyta Measurement method Conductive tissue Vegetation structure Humidity response of stomatal Nothofagus Xylem sap flow Canopy transpiration Canopy conductance
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Summary:	Tree transpiration was determined by xylem sap flow and eddy correlation measurements in a temperate broad-leaved forest of Nothofagus in New Zealand (tree height: up to 36 m, one-sided leaf area index: 7). Measurements were carried out on a plot which had similar stem circumference and basal area per ground area as the stand. Plot sap flux density agreed with tree canopy transpiration rate determined by the difference between above-canopy eddy correlation and forest floor lysimeter evaporation measurements. Daily sap flux varied by an order of magnitude among trees (2 to 87 kg$\text{day}^{-1}\ \text{tree}^{-1}$). Over 50% of plot sap flux density originated from 3 of 14 trees which emerged 2 to 5 m above the canopy. Maximum tree transpiration rate was significantly correlated with tree height, stem sapwood area, and stem circumference. Use of water stored in the trees was minimal. It is estimated that during growth and crown development, Nothofagus allocates about 0.06 m of circumference of main tree trunk or 0.01 m2of sapwood per kg of water transpired over one hour. Maximum total conductance for water vapour transfer (including canopy and aerodynamic conductance) of emergent trees, calculated from sap flux density and humidity measurements, was 9.5 mm s-1that is equivalent to 112 mmol m-2s-1at the scale of the leaf. Artificially illuminated shoots measured in the stand with gas exchange chambers had maximum stomatal conductances of 280 mmol m-2s-1at the top and 150 mmol m-2s-1at the bottom of the canopy. The difference between canopy and leaf-level measurements is discussed with respect to effects of transpiration on humidity within the canopy. Maximum total conductance was significantly correlated with leaf nitrogen content. Mean carbon isotope ratio was -27.76±0.27‰ (average ± s.e.) indicating a moist environment. The effects of interactions between the canopy and the atmosphere on forest water use dynamics are shown by a fourfold variation in coupling of the tree canopy air saturation deficit to that of the overhead atmosphere on a typical fine day due to changes in stomatal conductance.
Bibliography:	ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23 ObjectType-Article-1 ObjectType-Feature-2
ISSN:	0029-8549 1432-1939
DOI:	10.1007/bf00317623