Can we define ecosystems? On the confusion between definition and description of ecological concepts

Sound definitions of its basic concepts are fundamental to every scientific discipline. In some instances, like in the case of the ecosystem concept, the question arises if we can define such concepts at all. And if we can define them, how should we choose from the multiple definitions available? And what are the preconditions for a scientifically sound and useful definition? On the basis of the ecosystem concept, this paper illustrates a major, often neglected distinction in the definition of ecological concepts, namely that between defining criteria and additional descriptive statements connected to those definitions. As is demonstrated by examples from the literature, mixing up these categories leads to false inferences about the properties of physical objects (e.g. a particular forest) subsumed by the concept (e.g. the ecosystem). As a further consequence, this inference becomes problematic in terms of theory development and/or the application of ecological concepts for management decisions.