Vegatation Classification
Vegetation of mature ecosystems is emphasized in Biogeoclimatic Ecosystem Classification as it is considered to be the best integrator of the combined influence of the environmental factors affecting a site. Vegetation units are determined by grouping plot data and then comparing the resulting units in a series of vegetation tables.
The outcome is a hierarchy of vegetation units with plant class being the most general. Classes are divided into plant orders, orders into plant alliances, alliances into plant associations and associations into plant subassociations. Plant associations are the basic unit of the vegetation classification hierarchy. Each unit is differentiated by a diagnostic combination of species. Tree species, or broad forest types, are emphasized at the upper levels of the hierarchy (classes/orders), and understory vegetation at the lower levels, however, floristic similarity is used to group units.
The vegetation classification is integral to development of the other classifications in BEC because vegetation is readily observed and described, and differences in vegetation reflect climatic, site and successional relationships. Plant associations and subassociations are important for determining biogeoclimatic subzones and variants (Climatic classification), and site associations (Site classification), respectively. Vegetation is used in the field to identify climatic or site units, but the vegetation hierarchy is in the "background".