Simple models of transpiration, e.g., the Penman-Monteith equation, treat
atmospheric conditions as driving variables. In fact, transpiration modifies temperature
and humidity throughout the convective boundary layer, creating feedbacks that stabilize
the water use of vegetation. This thesis concentrates on the new empirical relationships
proposed by Monteith (1995), for developing simple models of feedback, and then applies
these relationships to data from the Oregon Cascades. Monteith showed that there is
strong laboratory evidence to support a linear relationship between leaf transpiration rate
and leaf conductance. If this relationship holds for vegetation in the field, simple models
to explain the diurnal variation of canopy conductance can be developed. When this
model was applied to data from a Douglas fir forest, canopy conductance changed in
response to transpiration rate, rather than to saturation deficit, as has been previously
assumed. Monteith also reanalyzed data from McNaughton and Spriggs (1989) which
explored the dependence of the Priestley-Taylor coefficient alpha on surface parameters.
He showed that there is a linear relationship between alpha and surface conductance. By
combining this "demand function" with the physiological "supply function" described
earlier, the PMPT model is developed in which evaporation rate depends on physical
feedbacks in the convective boundary layer and physiological feedbacks within plants.
The thesis will focus on the results of the research done using this model. The PMPT
model will then be compared with other simple models of transpiration in order to
determine its applicability. / Graduation date: 1997
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28699 |
| Date | 25 February 1997 |
| Creators | Heinsch, Faith Ann |
| Contributors | Unsworth, Michael H. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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