The U.S. National Vegetation Classification System Hierarchy Level

Classification Level [Example in braces]

Class Growth form and structure of vegetation [Woodland]

Subclass Growth form characteristics, e.g., leaf phenology [Deciduous Woodland]

Group Leaf types, corresponding to climate [Cold-deciduous Woodland]

Subgroup Relative human impact (natural/semi-natural, or cultural) [Natural/Semi-natural]

Formation Additional physiognomic and environmental factors, including hydrology [Temporarily Flooded Cold-deciduous Woodland]

Alliance Dominant/diagnostic species of uppermost or dominant stratum [Populus deltoides Temporarily Flooded Woodland Alliance]

Association Additional dominant/diagnostic species from any strata [Populus deltoides - (Salix amygdaloides) / Salix exigua Woodland]