Document: AND-3-32-31

Ecological optimality in semi-arid woodlands: Testing Eagleson's ecohydrological equilibrium.

KERKHOFF, A.J.*, S.N.MARTENS and B.T.MILNE

University of New Mexico, Albuquerque, NM 87131 USA ¹

Abstract:
Eagleson's ecological optimality theory predicts that water-limited natural vegetation systems exist in a stable equilibrium with their climatic and soil environments. According to Eagleson's hypothesis, the equilibrium is maintained in the short term by canopy adjustments toward a density that minimizes average annual water demand stress. Alternatively, we hypothesize that fitness pressures may act to maximize canopy evapotranspiration. Eagleson's water balance framework allows us to predict optimal canopy densities, and their variation over a complex topographic landscape, based on spatially explicit estimates of climate, soil, and vegetation parameters from the Sevilleta LTER. We confront the alternative optimal canopy predictions (minimum stress vs. maximum transpiration) with empirical canopy estimates drawn from high resolution, remotely sensed data. Empirical canopy densities are generally intermediate between the two hypotheses, and the spatial patterning of residual variation is related to both model assumptions and landscape characteristics. Our results highlight the need to incorporate fuller descriptions of canopy transpiration and run-on dynamics in future models, as well as the need to understand the scaling of ecohydrological processes. The statistical mechanical basis of Eagleson's approach provides a powerful (and largely unutilized) method for developing biophysical models of landscape ecological dynamics, and the analytic nature of the resulting theory represents a useful alternative to complicated numerical simulations.

Keywords: water-balance, ecological optimality, pinyon-juniper woodlands

This abstract is being presented at: 8:00 AM in session:
Oral Session #45: Water Relations in Shrubs and Annuals.