Climax is a theoretical, ecological notion intended to describe a relatively stable community that is in equilibrium with environmental conditions, and occurring as the terminal, end-point of succession.
One of the early proponents of the concept of climax was the American ecologist, Frederic Clements. In an important publication in 1916, he theorized that there was only one true climax community for any given climatic region. This so-called climatic climax would be the eventual end-point of all successions, whether they started after fire, deglaciation, or other disturbances, or even from a pond or lake filling in, and regardless of soil type. This monoclimax theory was criticized as too simple, and was challenged by other ecologists. A.G. Tansley proposed a more realistic polyclimax theory that accommodated the important successional influences of local soil type, topography, and disturbance history. In the early 1950s, R.H. Whittaker suggested that there were gradually varying climax types on the landscape, associated with continuous gradients of environmental variables. According to Whittaker, ecological communities vary continuously, and climax communities cannot be objectively divided into discrete types.
In a practical sense, it is not possible to identify the occurrence of a climax community. The climax condition may be suggested by relatively slow rates of change in the structure and function of old-growth communities, compared with earlier, more dynamic stages of succession. However, change in ecological communities is a universal phenomenon, so the climax state cannot be regarded as static. For example, even in old-growth communities, microsuccession is always occurring, associated perhaps with the death of individual trees. Moreover, if the frequency of return of stand-level disturbance events is relatively short, the old-growth or climax condition will not be reached.