COMPETITION AND CENTRIFUGAL ORGANIZATION OF PLANT-COMMUNITIES - THEORY AND TESTS

The concept of centrifugal organization integrates community ecology's two main conceptual approaches: description of gradients and study of process. Centrifugal organization describes distributional patterns of species and vegetation types along standing crop gradients that are caused by different combinations of environmental constraints, Gradients radiate outwards from a single core habitat to many different peripheral habitats. The assumed mechanism is a competitive hierarchy where weaker competitors are restricted to the peripheral end of the gradient as a result of a trade-off between competitive ability and tolerance limits. The benign ends of the gradients comprise a core habitat which is dominated by the same species. At the peripheral end of each axis. species with specific adaptations to particular sources of adversity occur. In wetlands, the core habitat has low disturbance and high fertility, and is dominated by large leafy species capable of forming dense canopies. Peripheral habitats are formed by different kinds and combinations of infertility and disturbance and support distinctive floras. The centrifugal organization model therefore allows us to predict the distribution of particular organisms (rare species) and to predict how changes to the conditions creating peripheral habitats will alter community composition.