HR: 14:25h
AN: A13C-04    [Abstracts]
TI: Optimum Conditions for Terrestrial Vegetation and Associated Vegetation Feedbacks to the Climate System
AU: * Kleidon, A
EM: akleidon@umd.edu
AF: Department of Geography and Earth System Science Interdisciplinary Center, 2181 Lefrak Hall University of Maryland, College Park, MD 20742 United States
AB: Terrestrial vegetation plays an important role in moderating the energy- and water fluxes at the land surface, thereby affecting climate. One of the fundamental features of terrestrial vegetation is its ability to adapt to its climatic environment, thereby maximizing its capacity to perform photosynthesis. Here I apply this concept of optimum adaptation to the parameterization of vegetation in a coupled dynamic vegetation-climate system model of intermediate complexity. I show that there are optimum values for key land surface characteristics, such as stomatal conductance, rooting zone depth, and surface roughness, for which the climatic conditions to do photosynthesis are optimal. These optima result from the close coupling of photosynthesis and transpiration in terrestrial vegetation that links the availability of carbon dioxide within the leaves to the rate of water loss by transpiration. Different rates of transpiration lead to a fundamental trade-off: increasing rates of transpiration increases the availability of carbon dioxide, but at the same time results in more clouds, thereby reducing the amount of incoming solar radiation. Threfore, there is an optimum at which the rate of photosynthesis is at a maximum. Sensitivity simulations with the coupled model show (a) that the resulting optimum values for these land surface characteristics are realistic; (b) that the associated climate is close to the present-day control climate; and (c) that the climate is unique in that the rate of continental evapotranspiration is maximized, leading to the most active hydrological cycle over land. Because realistic optima exist to which vegetation would adapt to, it is concluded that the resulting feedbacks of terrestrial vegetation to climatic perturbations are primarily negative, bringing climatic conditions back to the optimum.
DE: 3307 Boundary layer processes
DE: 1818 Evapotranspiration
DE: 1851 Plant ecology
DE: 0315 Biosphere/atmosphere interactions
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting