The Ecology of Secondary Succession

Rather than review the ample and expanding literature of succession, as Drury & Nisbet (12) have lately and nobly done, I propose to cover some recent developments in population biology that have profound implications for theories and patterns of secondary succession. Much of the conventional wisdom of successional theory rests on biased definitions and hidden assumptions. So I begin by defining what I mean by succession, and stating why I limit my discussion to secondary succession. Succession is a pattern of changes in specific composition of a community after a radical disturbance or after the opening of a new patch in the physical environment for colonization by plants and animals. If the physical environment remains con­ stant, eventually the changes in the specific composition of the community become undetectably slow or cease altogether. This late stage of succession is dignified by the term climax. The climax is often idealized as a state of constant specific composition, though of course the species and their relative abundances fluctuate statistically and vary from place to place as the physical environment changes along more or less perceptible gradients. Thus I concur with the concept of climax proposed by Whittaker (49, 50), that is, a pattern of species' abundances, which, while locally constant, varies from place to place in a continuous fashion. Because population biology treats interactions between organisms, I limit my discussion to secondary succession, the process of reestablishment of a reasonable facsimile of the original community after a temporary disturbance. Secondary succession is usually a result of interspecific competition, with pioneer species often beating later species to openings and perhaps outcompeting them in openings as well, but themselves producing an environment in which later species are competitively superior. Hence I ignore at least that component of succession that is a direct response of one or more species to secular changes in the environment: primary succession (e.g. as a lake fills with silt or as bare rock weathers to mineral soi!), seasonal succession, and succes­ sions that track climatic changes over geological time. For a short, thorough, and constructive account of successional patterns see Whittaker's (54) book and its impending new edition. Odum (37, 38) concisely