Natural Vegetation Classification

Natural (and semi-natural) vegetation is defined as “vegetation where ecological processes primarily determine species and site characteristics”. Human activities may influence vegetation interaction, but do not dominate or remove ecological processes.

The top three levels (class, subclass, formation) are coarse and describe major ecological categories on a global scale. These levels emphasize physiognomy, a combination of the external appearance of vegetation, its vertical structure, and the growth forms of the dominant taxa. The middle levels (division, macrogroup, group) reflect distinctive combinations of species in the context of regional and continental environmental variables and processes such as water cycles and fire patterns.  Biogeography and florists are increasingly integrated at the three middle levels. The lowest levels (alliance and association) are the most fine-grained, based on diagnostic and/or dominant species and compositional similarity reflecting local to regional environmental factors.

The relationship between the new hierarchy levels and classification criteria is depicted in the diagram below.

The following table shows criteria and examples of the levels of the revised National Vegetation Classification hierarchy for natural vegetation.

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A description of each classification concept is available for those levels that have been reviewed.