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Boundary layer conductance for contrasting leaf shapes in a deciduous broadleaved forest canopy

Stokes, Victoria J.; Morecroft, Michael D.; Morison, James I. L.. 2006 Boundary layer conductance for contrasting leaf shapes in a deciduous broadleaved forest canopy. Agricultural and Forest Meteorology, 139. 40-54. 10.1016/j.agrformet.2006.05.011

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Abstract/Summary

A new method of constructing light, flexible and more realistic replica leaves for continuous determination of leaf boundary layer conductance to heat transfer () was developed and tested in a mature oak (Quercus robur L.) and sycamore (Acer pseudoplatanus L.) tree canopy. The replicas were used to determine the difference between oak and sycamore leaf in exposed sites in the upper canopy, the relationship of with wind speed, the seasonal changes in in the canopy as leaf cover developed, and values for Ω, the decoupling coefficient. The replicas showed similar gradients in temperature at their margins to those in real leaves. When exposed, the of the larger sycamore leaves was 66% of that of oak leaves under the same conditions. Linear relationships were found with and wind speed across the measured range of 0.3–3.5 m s−1, and flow in the replica boundary layers was laminar in all conditions. The leafless canopy produced a substantial sheltering effect, reducing by 12–28% in light winds. Sycamore replicas in the leafed canopy showed a 19–29% lower at a given external wind speed than when outside, but there was little difference between ‘sun’ and ‘shade’ position shoots, because of the density of the shoots, and the close branching pattern. In contrast, in oak at a given wind speed was 15–21% lower for ‘sun’ leaves than that for replicas outside the canopy, with a larger reduction (approximately 28%) in denser ‘shade’ sites. Although wind speed in the canopy was often low, leaves of both species were usually well coupled to the canopy airstream (Ω < 0.3). Sun leaves were substantially less well coupled than shade leaves, despite the lower shelter effect, because of their higher stomatal conductance values. In the lightest winds (<0.5 m s−1) and with high stomatal conductance, coupling may on many occasions be poor for sun leaves, particularly for the larger sycamore leaves

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1016/j.agrformet.2006.05.011
Programmes: CEH Programmes pre-2009 publications > Biodiversity > CC01A Detection and Attribution of Change in UK and European Ecosystems
CEH Sections: _ Ecosystem Assessment & Forecasting
ISSN: 0168-1923
Additional Keywords: boundary layer conductance, oak, sycamore, leaf shape, leaf temperature, transpiration
NORA Subject Terms: Botany
Ecology and Environment
Date made live: 14 May 2008 08:30
URI: http://nora.nerc.ac.uk/id/eprint/2923

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