GRADIENTS IN ECOLOGICAL-SYSTEMS

In this paper, the potentials of a holistic and hierarchical gradient approach to ecosystem analysis and ecosystem theory are discussed, usi ng some examples from the ecosystem research project in the Bornhoved Lakes Region (Northern Germany). In the gradient concept, which origin ates in the thermodynamic non-equilibrium principle, structural ecosys tem properties are comprehended as concentration gradients in space an d time. They build up potentials to carry out mechanical work, chemica l reactions, or biological interactions. Ecosystem function is defined as the general characteristic of the systems' gradients dynamics. The gradient concept is theoretically discussed as an integrating tool fo r the aspects of thermodynamics, self-organization, and hierarchy theo ry. It helps to avoid inadequate reductions from holistic data sets to non-representative theoretical variables. Also, it can be used as an indicator to test theoretical hypotheses which are often based on non- measureable variables, and it may improve the cooperation between theo reticians and empirical ecologists. The necessary interfaces between t his strategy and important ecosystem theoretical ideas are briefly des cribed in this text. As an illustration, three aspects of the gradient concept are presented in empirical case studies: spatial, temporal, a nd functional gradients. In these examples, the gradient systems of na ture-near ecosystems are compared with those of stressed ecosystems. O n this basis, the applicability of the gradient concept in theory and practice is discussed. (C) 1998 Elsevier Science B.V. All rights reser ved.