CNVC Hierarchy Levels - Criteria

Hierarchy Level

Criteria

Upper: Physiognomy plays a predominant role.

  L1 – Formation Class

A vegetation unit that is defined by a broad combination of general dominant growth forms that are adapted to basic moisture, temperature, and/or substrate or aquatic conditions.

  L2 -  Formation Subclass

A vegetation unit that is defined by a combination of general dominant and diagnostic growth forms that reflect global mega- or macroclimatic factors driven primarily by latitude and continental position, or that reflect overriding substrate or aquatic conditions.

  L3 – Formation

A vegetation unit that is defined by a combination of dominant and diagnostic growth forms that reflect global macroclimatic conditions as modified by altitude, seasonality of precipitation, substrates, and hydrologic conditions.

Middle: Both floristics and physiognomy play a significant role.

  L4 – Division

A vegetation unit that is defined by combinations of dominant and diagnostic growth forms and a broad set of diagnostic plant species that reflect biogeographic differences in composition and continental differences in mesoclimate, geology, substrates, hydrology, and disturbance regimes

  L5 – Macrogroup

For upland vegetation that includes zonal vegetation: a vegetation unit that is defined by regionally distinct subsets of plant species composition, abundance and/or dominance, representing primary regional climatic gradients as reflected in vegetation patterns on circum-mesic ("zonal") sites.

For azonal vegetation: see EcoVeg interpretive guidelines, Table 4.

  L6 – Group

For upland vegetation that includes zonal vegetation: an aggregation of Alliances within the regional vegetation defined by a Macrogroup, with consistency in dominant and/or diagnostic species. Groups describe regionally generalized  vegetation pattterns attributable to ecological drivers such as edaphic or geological conditions within the Macrogroup.

For azonal vegetation: see EcoVeg interpretive guidelines, Table 4.

Lower:  Floristics plays a predominant role.

  L7 – Alliance

An aggregation of Associations, with consistency in dominant and/or diagnostic species, describing regionally repeating vegetation patterns at the local to sub-regional scale. Alliances are created by grouping Associations that are ecologically “related” into more generalized ecological units

  L8 – Association

A plant community type with consistency of species dominance and overall floristic composition, having a clearly interpretable ecological context in terms of site-scale climate, substrate and/or hydrology conditions, moisture/nutrient factors or disturbance regimes, as expressed by diagnostic indicator species.