A model of disturbance equilibration

The contemporary ‘non-equilibrium’ paradigm in ecology acknowledges that ecosystems and their component floral and faunal communities show historic dynamism, not unchanging constancy (Shugart & West 1981; Pickett et al. 1992; Hengeveld 1994). In formulating a hierarchical view of landscape ecology, Urban et al. (1987) modelled broad classes of forest disturbances and corresponding landscape scales. A reference level is the scale at which a disturbance is observed as an ‘interesting event’. At the next, lower landscape scale the disturbance has a significant impact and explanatory mechanisms may be investigated. At the level above the reference scale, the ‘event’ may be viewed in a broader ecological context where its impact has been buffered and successfully incorporated. Urban et al. (1987) suggested that ‘a disturbance regime that can be incorporated is not disturbing at all’. Extending this perspective to anthropogenic perturbations, Urban et al. (1987) praised the ‘wisdom’ of foresters for discovering clear-cut harvesting as a forest management strategy that mimics natural disturbances. It might be possible for a reader with a pro-exploitation agenda to misinterpret the meaning of the model presented in Urban et al. (1987) and attempt to use it in support of forest management that is destructive to overall ecosystem health, thereby detracting from Urban et al.'s (1987) and Shugart and West's (1981) pioneering contributions to the field of landscape ecology. It could be argued that we only need look to a higher landscape scale in the model of equilibration to find a level at which clear-cuts need no longer be considered forest disturbances.