IMPLICATIONS OF MODERN SUCCESSIONAL THEORY FOR HABITAT TYPING - A REVIEW

The habitat type classification system (HTCS) is widely used in the we stern United States and has recently been applied in the Lake States. This classification system is based on three premises, two of which ar e embodied in the Clementsian theory of succession. These premises are (1) the climatic or potential climax is the same for all sites that h ave similar growing environments within a region, (2) the climax stage of succession reflects the inherent productivity of a site better tha n any other stage, and (3) after disturbance, the understory stabilize s more quickly than, and independent of, the overstory. The current un derstanding of succession, disturbance, and interactions between overs tory and understory was reviewed and showed that the three premises on which HTCSs are based cannot be accepted a priori as widely applicabl e. In particular, it was concluded that (1) most sites will never supp ort a climax stage (sensu Clements); (2) disturbances, past land use, and stochastic events can lead to multiple pathways on a single ''type '' of site; and (3) the overstory often exerts a significant effect on the understory. Thus, a land classification system that relies solely or heavily on vegetation, such as the HTCS, should be based on a new theoretical foundation and incorporate the known variation and stochas ticity of vegetation dynamics. This means a new standard and additiona l analyses must be incorporated during the development of HTCS's so th at the systems are more accurate, widely applicable and as useful as p ossible.