Current theory suggests that ecosystem stability is a function of physical and biological complexity. Frequent disturbances may reduce this complexity and thereby destabilize ecosystems, making them more susceptible to future perturbations. Theory predicts that ecosystems with large scale physical (i.e. geomorphic) complexity can effectively maintain structural integrity when impacted by catastrophic disturbances. This project will develop a quantitative model that links changes in ecosystem structural complexity resulting from disturbances, to stability. Because streams are strongly influenced by landscape geomorphology and respond relatively quickly to disturbances, stream ecosystems will be used. Disturbance-stability relationships will be assessed in terms of logging impacts, landslides, and floods on general stream ecosystem dynamics, with special emphasis on fish population responses. To address the importance of large and small scale physical complexity, the model will be hierarchically structured (i.e. contain basin, stream reach, and channel unit scales), and focus on examination of logging impacts at the stream reach scale. Hypotheses developed and evaluated with this model should provide new insights into how geomorphic complexity interacts with disturbance to structure ecosystems and set the stage for the success or failure of biotic components.
