Toward Conceptual Cohesiveness: a Historical Analysis of the Theory and Utility of Ecological Boundaries and Transition Zones

Ecological transition zones are increasingly recognized as systems that play a critical role in controlling or modifying flows of organisms, materials, and energy across landscapes. Many concepts describing transitional areas have been proposed over the years, such as the prevalent and durable ecotone concept. Confusion among ecologists and land managers about transition zone concepts and the isolation of studies that use only one transition concept can hinder unified progress in understanding these key systems. Currently, a movement toward conceptual synthesis under the umbrella concept of 'ecological boundary' is underway. Here we examine the history and theoretical baggage of the ecotone, riparian zone, and several other concepts. Subsequently, we present a conceptual cluster analysis, which facilitates a better understanding of the similarities and differences between boundary and transition concepts. We emphasize the hierarchical nature of these concepts: higher-level synthetic concepts can be used in the development of theory, whereas lower-level concepts allow more specificity and the formulation of operational definitions. Finally, we look briefly at the utility and future use of boundary and transition zone concepts.