Oral Session - Landscape Models to Predict Future Landscape Change - Day 1 Chair(s): Neale, Anne¹, ¹ Landscape Ecology Branch, Las Vegas, NV
Wednesday, March 31, 2004 10:00 AM - 12:00 PM Apollo Room 5

Terrain as a selective agent in the evolution of plant species diversity. Milne, Bruce^*,1, ¹ Department of Biology, Albuquerque, NM, USA

ABSTRACT- Plants colonized land 580 million years ago and have since evolved to occupy an extraordinary range of habitats and land surface conditions. A dynamical theory of the coupling between plants and terrain includes feedback between: (a) plants as arbiters of the water available for erosion and (b) terrain as supplier of plant resources. Terrain and plants are coupled via the infiltration rate which divides precipitation into two components: evapotranspiration and flow, that correspond to net primarly production and erosion potential, respectively. Natural selection should favor intermediate infiltration rates to maximize fitness via allocation to roots, shoots, and alternative physiological pathways, as evident in the Columbia River Basin. A dynamical formulation for infiltration rate as a function of plant resources and terrain dynamics exhibits stable equilibria in agreement with the selection argument. Moreover, the equilibria are unstable with respect to elevation, suggesting that uplift and erosion select for plants to adjust infiltration rates to be better suited to new environments. Maps of the partial derivatives of infiltration indicate where plants are most sensitive to disturbances that alter shear stress, say during flooding, versus responses to fluctuations in potential evapotranspiration and precipitation. A related expression for infiltration over arbitrary sized basins enables assessments of risks for vegetation change at multiple scales where local controls give way to latitudinal gradients in available energy.

KEY WORDS: plants, terrain, infiltration, dynamics, selection