A hierarchical framework for the analysis of scale

Landscapes are complex ecological systems that operate over broad spatiotemporal scales. Hierarchy theory conceptualizes such systems as composed of relatively isolated levels, each operating at a distinct time and space scale. This paper explores some basic properties of scaled systems with a view toward taking advantage of the scaled structure in predicting system dynamics. Three basic properties are explored:(1) hierarchical structuring, (2) disequilibrium, and (3) metastability. These three properties lead to three conclusions about complex ecological systems. First, predictions about landscape dynamics can often be based on constraints that directly result from scaled structure. Biotic potential and environmental limits form a constraint envelope, analogous to a niche hypervolume, within which the landscape system must operate. Second, within the constraint envelope, thermodynamic and other limiting factors may produce attractors toward which individual landscapes will tend to move. Third, because of changes in biotic potential and environmental conditions, both the constraint envelope and the local attractors change through time. Changes in the constraint structure may involve critical thresholds that result in radical changes in the state of the system. An attempt is made to define measurements to predict whether a specific landscape is approaching a critical threshold.Research supported in part by the Ecological Research Division Office of Health and Environmental Research, US Department of Energy under contract No. DE-AC05-840R21400 to Martin Marietta Energy Systems Inc., and in part by the Ecosystem Studies Program, National Science Foundation, under Interagency Agreement No. NSF BSR 8315185 to the Department of Energy. Publication No. 3381, Environmental Sciences Division, Oak Ridge National Laboratory.Dr. Johnson's participation was supported in part by an appointment to the Postgraduate Research Training program under contract DE-AC05-76OR00033 between the U.S. Department of Energy and Oak Ridge Associated Universities, Oak Ridge, TN 37831.