Determinism, Chaos and Stochasticity in Plant Community Successions: Consequences for Phytosociology and Conservation Ecology

Vegetation dynamics has long been studied from a deterministic perspective, leading to important concepts like climax, equilibrium and reversibility. In recent decades, the emergence of the theory of chaos has changed our vision of natural laws. New concepts such as non-equilibrium, heterogeneity, disturbance and irreversibility have increasingly become popular. Some ecological successions have even been considered as stochastic and thus their outcome a matter of chance. Here, I briefly review these three paradigms, within the special framework of vegetation typology and conservation ecology. I conclude that all successions are, at least partly, deterministic. The proportion of stochasticity depends mainly on the size and composition of the regional species pool, and is likely to occur in early-successional stages. When the lack of acute disturbance allows a succession to develop, the late-successional stages usually converge toward a ‘strange attractor’, i.e. the climax. Short-term and/or small-scale monitoring are common biases leading to conclude that determinism does not exist in plant community successions.