HR: 1340h
AN: H53E-0523    [Abstracts]
TI: A Test of the Optimality Approach to Modelling Canopy gas Exchange by Natural Vegetation
AU: * Schymanski, S J
EM: schymans@cwr.uwa.edu.au
AF: Centre for Water Research, The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009 Australia
AU: Sivapalan, M
EM: sivapala@uiuc.edu
AF: Department of Geography, University of Illinois at Urbana-Champaign, 220 Davenport Hall, MC-150 607 South Mathews Avenue, Urbana, IL 61801 United States
AU: Roderick, M L
EM: Michael.Roderick@anu.edu.au
AF: CRC for Greenhouse Accounting, The Australian National University, GPO Box 475, Canberra, ACT 2601 Australia
AU: Beringer, J
EM: jason.beringer@monash.edu.au
AF: School of Geography and Environmental Science, Monash University, PO Box 11A, Clayton, VIC 3800 Australia
AU: Hutley, L B
EM: lindsay.hutley@cdu.edu.au
AF: School of Science & Primary Industry, Charles Darwin University, Casuarina Campus , Darwin, NT 0909 Australia
AB: Natural vegetation has co-evolved with its environment over a long period of time and natural selection has led to a species composition that is most suited for the given conditions. Part of this adaptation is the vegetation's water use strategy, which determines the amount and timing of water extraction from the soil. Knowing that water extraction by vegetation often accounts for over 90% of the annual water balance in some places, we need to understand its controls if we want to properly model the hydrologic cycle. Water extraction by roots is driven by transpiration from the canopy, which in turn is an inevitable consequence of CO₂ uptake for photosynthesis. Photosynthesis provides plants with their main building material, carbohydrates, and with the energy necessary to thrive and prosper in their environment. Therefore we expect that natural vegetation would have evolved an optimal water use strategy to maximise its `net carbon profit' (the difference between carbon acquired by photosynthesis and carbon spent on maintenance of the organs involved in its uptake). Based on this hypothesis and on an ecophysiological gas exchange and photosynthesis model (Cowan and Farquhar 1977; von Caemmerer 2000), we model the optimal vegetation for a site in Howard Springs (N.T., Australia) and compare the modelled fluxes with measurements by Beringer, Hutley et al. (2003). The comparison gives insights into theoretical and real controls on transpiration and photosynthesis and tests the optimality approach to modelling gas exchange of natural vegetation with unknown properties. The main advantage of the optimality approach is that no assumptions about the particular vegetation on a site are needed, which makes it very powerful for predicting vegetation response to long-term climate- or land use change. Literature: Beringer, J., L. B. Hutley, et al. (2003). "Fire impacts on surface heat, moisture and carbon fluxes from a tropical savanna in northern Australia." International Journal of Wildland Fire 12(3-4): 333-340. - Cowan, I. R. and G. D. Farquhar (1977). Stomatal Function in Relation to Leaf Metabolism and Environment. Integration of activity in the higher plant. D. H. Jennings. Cambridge, Cambridge University Press: 471-505. - von Caemmerer, S. (2000). Biochemical Models of Leaf Photosynthesis. Collingwood, CSIRO Publishing.
DE: 1813 Eco-hydrology
DE: 1818 Evapotranspiration
DE: 1847 Modeling
DE: 1851 Plant ecology (0476)
SC: Hydrology [H]
MN: Fall Meeting 2005