Tropical Grasslands (1994) Volume 28, 195–205

State and transition models for rangelands.
1. Successional theory and vegetation change


Botany Department, University of New England, Armidale, NSW, Australia


Traditional views of successional change in vegetation envisage orderly sequences of vegetation types leading from bare rock or water etc. through to stable climax vegetation. Disturbances are seen as discrete events involving the destruction or removal of plant biomass followed by secondary succession leading back to the original, stable, climax vegetation.
The idea that only one stable type of climax vegetation exists for each climatic zone was seriously questioned during the middle of this century, leading to the polyclimax and climax pattern hypotheses. The factorial approach to vegetation dynamics also led to serious questions being raised about the validity of the monoclimax theory.
If vegetation is assumed to be inherently unstable, and if the definition of disturbance is extended to include a change over time in any of the state factors controlling the plant species composition at any location, then a vegetation dynamics paradigm more appropriate to a highly variable environment can be constructed. The state and transition model fulfils these requirements and leads to a more pro-active approach to vegetation management than is possible with the traditional plant succession model.

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