Other Classification Systems

The federal government and other agencies use a system of forest classification based on the

  • overall growth form (physiognomy) of the community and its plants,
  • dominant vegetation and species composition.

The Nature Conservancy and the network of Natural Heritage programs developed this system and continue to refine it. It is a hierarchical system that can be used at the broadest level (gross appearance) and at the finest level (species composition of a forest).

This combination makes the system useful for a broad range of scientists, from people interested in mapping forest distributions, to those studying the populations of different plant species.

The most inclusive level of this classification system is the 'class,' which is based on the type of dominant vegetation, its relative percent cover, and its height. Forests, woodlands, shrublands, and herbaceous plant-dominated ecosystems, for example, are 'classes.'

The system divides classes by leaf types (for example, evergreen, deciduous, and mixed evergreen-deciduous) and further subdivides through 'formation,' a level that considers appearance and environmental factors.

The final two subdivisions in the scheme, 'alliance' and ‘association’ are based on species composition (the different plants that occur together in the community).

The other 5 levels above them are based on gross appearance (physiognomy). Although these subdivisions consider primarily the dominant vegetation, they also take into account "diagnostic" species – species that distinguish a forest type from another, for example.