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Elevation and Transpiration: Some Theoretical Considerations with Special Reference to Mediterranean-Type Climate

J. Gale
Journal of Applied Ecology
Vol. 9, No. 3 (Dec., 1972), pp. 691-702
DOI: 10.2307/2401898
Stable URL: http://www.jstor.org/stable/2401898
Page Count: 12
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Elevation and Transpiration: Some Theoretical Considerations with Special Reference to Mediterranean-Type Climate
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Abstract

The hypothesis that hill and mountain environment is conducive to xeromorphism is examined in relation to meteorological factors and especially with regard to regions having Mediterranean-type climate. The following conclusions are drawn. Under isothermal conditions decrease of air pressure with elevation enhances potential transpiration, by increasing the leaf to air water vapour gradient and by increasing the diffusivity of water vapour in air. The change in the rate of potential transpiration with elevation is modified in both degree and direction by the character of the temperature lapse rate. Under isothermal, and much more so under temperature inversion conditions, the lower barometric pressure and increased solar radiation flux, which are associated with increasing height, combine to produce very high rates of potential transpiration. When temperature falls with height at rates approaching the average mid-latitudinal lapse rate (-0.0065 C/m), air temperature becomes the dominant factor and transpiration falls with increasing height. The above considerations refer to rates of potential transpiration. However, plants often close their stomata in response to high rates of transpiration and this not only lowers the rate of transpiration but also reduces growth and contributes to the development of xeromorphism.

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