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Transpiration and canopy conductance in a pristine broadleaved forest of "Nothofagus" : an analysis of xylem sap flow and eddy correlation measurements

Title data

Köstner, Barbara ; Schulze, Ernst-Detlef ; Kelliher, Francis M. ; Hollinger, Dave Y. ; Byers, J. N. ; Hunt, J. E. ; McSeveny, T. M. ; Meserth, R. ; Weir, P. L.:
Transpiration and canopy conductance in a pristine broadleaved forest of "Nothofagus" : an analysis of xylem sap flow and eddy correlation measurements.
In: Oecologia. Vol. 91 (September 1992) Issue 3 . - pp. 350-359.
ISSN 1432-1939
DOI: https://doi.org/10.1007/BF00317623

Abstract in another language

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 day-1 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 m2 of 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-1 that is equivalent to 112 mmol m-2 s-1 at the scale of the leaf. Artificially illuminated shoots measured in the stand with gas exchange chambers had maximum stomatal conductances of 280 mmol m-2 s-1 at the top and 150 mmol m-2 s-1 at 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 four-fold 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.

Further data

Item Type: Article in a journal
Refereed: Yes
Additional notes: BAYCEER7004
Institutions of the University: Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Biology > Chair Plant Ecology
Research Institutions > Research Centres > Bayreuth Center of Ecology and Environmental Research- BayCEER
Faculties
Faculties > Faculty of Biology, Chemistry and Earth Sciences
Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Biology
Research Institutions
Research Institutions > Research Centres
Result of work at the UBT: Yes
DDC Subjects: 500 Science
Date Deposited: 12 Nov 2015 07:44
Last Modified: 05 Apr 2016 13:05
URI: https://eref.uni-bayreuth.de/id/eprint/22481