The Steady State as a Component of the Landscape

Models of ecosystem development usually portray autogenic succession as an orderly progression of biologic changes (e.g., Odum, 1969; Woodwell, 1974). The macroenvironment within which development occurs is presumed to be more or less constant throughout the autogenic sequence. Yet every terrestrial ecosystem is subjected to a range of disturbances varying from those that barely alter the structure, metabolism, or biogeochemistry of the ecosystem to those that wholly or dramatically change the system. Defining “disturbance” is itself a considerable problem, because it is difficult to draw a line between biological and physical-chemical events that may be considered within the scope of autogenic development and other events that might be considered to seriously deflect the autogenic pattern. In developing the Hubbard Brook Biomass Accumulation Model (Chapter 1) of ecosystem development, we followed the procedures of Odum (1969), Botkin et al. (1972a,b), and Woodwell (1974) and emphasized autogenic development, while deemphasizing exogenous disturbance. This was a necessary decision if our model was to reflect an uninterrupted sequence from the initiation of secondary development to the establishment of the steady state.