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This chapter presents an overview of landscape-level research developments during the past 30 years; addresses how landscape-level ecological changes, instrumentation refinement, and large-scale perturbations have changed the field of landscape ecology . The chapter relates these changes to significant theories, principles, and approaches that have emerged in landscape ecology during the past three decades (i.e., since the Allerton Park Workshop).

“Ecological Succession” is an ordered progression of structural and compositional changes in communities toward an eventual unchanging condition, the climax community 1 –3. The term “Community” is used in two ways 4. The “Abstract Community” refers to an abstract group of organisms that recurs on the landscape, a definition, which usually carries with it an implication of a level of integration among its parts that in extreme could be called organismal or quasi-organismal; the “Concrete Community” concept refers to the collection of organisms found at a specific place and time. These terms and their meanings are topics of significant debate among ecologists, both historically and today 5, 6. These differences in the meaning and cause of ecological succession strongly affect the formulation of policies for ecosystems management and restoration.

Studies of forest succession characteristically rely heavily on inference to order the spatial pattern of forest stands (usually on a regularly disturbed landscape) into a temporal pattern. The inferential structure used to arrange these data is, in a sense, a “theory of succession,” and the relation between the artificially ordered successional pattern and the ordering theory are, of necessity, tautological. This circularity persists regardless of the particular theory of succession (monoclimax, polyclimax, multiple paths, etc.) to which an ecologist happens to subscribe. The fact that both the observation data sets and the theory may both be quite elaborate makes it difficult to test the theories of succession. In this chapter, we shall take an alternate approach to studying successional dynamics. Instead of a direct and long-term observation of vegetation plots or a synthetic ordering of several plots, we shall use a set of reasonably detailed computer models of forest dynamics to explore system-level responses of different ecosystems. This simulation technique does not rely upon inferences made regarding temporal and spatial scales as do empirical studies of vegetation dynamics.

It sometimes seems natural to separate ecologists by a dichotomy of data- collecting, direct-observation oriented scientists and computer-oriented modelers. However, in the most general sense, any ecologist regularly uses conceptual models to structure scientific endeavor. It is these models that give intrinsic meaning to ecological data. Most scientists realize that the reason one collects the information needed for a particular study comes from a long tradition of concepts built over some number of years. The importance of conceptual models to scientists should not be underestimated in any ecological studies, long- term or otherwise.

Systems analysis in ecology has tended to condense and aggregate complex systems, a tendency that has a tradition going back to the classic work of Lindeman (1942). This orientation has been reinforced by a hearty interest in systems analysis techniques that use a small number of differential equations to represent the compartments into which an ecosystem is divided (for examples see Patten 1971, 1972, 1975, 1976; Shugart and O’Neill 1979). The use of such models in the synthesis of element cycles is such that compartment models and “box and arrow” diagrams dominate most documentations of ecosystem element cycles. However, several of the preceding chapters cite the need to incorporate mechanisms and processes in ecological models to a greater degree to further our understanding of ecosystem dynamics.