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1. The pioneering work of Peter Eagleson has been proposed as a theoretical basis for ecohydrology. Central to the theory are three ’ecological optimality hypotheses’ which represent ecologically important aspects of atmosphere-soil-vegetation interactions.

2. The model and its underlying assumptions have never been evaluated in an explicitly ecological context. We examine each of the three optimality hypotheses in turn and test the ability of the model to make ecologically relevant predictions using climate, soil and vegetation data from a semi-arid woodland site in central New Mexico, USA.

3. We find that all three of the optimality hypotheses are ecologically flawed. While we could qualitatively reproduce previously published results, model behaviour under novel conditions was highly variable and frequently unrealistic.

4. The poor performance of the model was probably due to the inadequate treatment of water-limited transpiration in its original derivation. The theory thus requires redevelopment for ecological application, and we suggest several strands of research that could contribute to its improvement.