PARENT SESSION
Oral Session #2: Thermodynamics and Complexity. Presiding: T. Allen.
Monday, August 6, 2001. 8:00 AM to 11:45 AM. Madison Ballroom D.
Complexity in terrestrial ecosystems as a consequence of thermodynamics: Experiments on a small-scale system.
Havlicek, Tanya 1, Allen, T.F.H.1, Vullings, Nicole1, Norman, John1, 1
ABSTRACT- A reformulated Second Law of Thermodynamics for open systems suggests complex ecosystems are better than simple ecosystems at dissipating the heat gradient between the earth's surface and outer space. If complexity can be measured by heat dissipation, this would provide a simple metric (radiometric temperature) that is linked to a specific function to investigate terrestrial ecosystems. Comparative studies have shown more complex ecosystems, in diversity and canopy architecture, have cooler surface temperatures than simpler systems. Our purpose was to create experimental ecosystems in controlled environments to investigate how complexity develops in ecosystems. We grew soybeans (Glycine max) in wind chambers with overstory (fast) or understory(slow) wind conditions. Infrared thermometers measured radiometric temperature of the vegetation. After the rearing period, plants were accommodated to overstory or understory wind conditions and mixed into two-layered vegetations. "Natural" mixes contained an overstory of plants reared in fast wind and an understory of plants reared in slow wind. 'Inverted' mixes contained plants in the opposite configuration. A comparison of mixes showed plants reared in fast wind behaved similarly in both mixes but the plants reared in understory wind dissipated less energy in the inverted mix (p-value<0.001). In the natural mix, understory wind reared plants are placed in a protective context, sheltered from strong winds by the overstory. A contextual hierarchical relationship between the whole vegetation and its constituents indicates complexity and conveys greater dissipative function.
KEY WORDS: thermodynamics, complexity, ecosystem, experiment