Basic Concepts
The BEC system groups ecosystems at three levels of integration: regional, local, and chronological.
At the regional level, vegetation, soils, and topography are used to infer the regional climate and to identify geographic areas that have relatively uniform climate. These geographic areas are termed biogeoclimatic units.
At the local level, segments of the landscape are classified into site units that have relatively uniform vegetation, soils, and topography. Several site units are distributed within each biogeoclimatic unit, according to differences in topography, soils, and vegetation.
At the chronological level of integration, ecosystems are classified and organized according to site-specific chronosequences. To do this, the vegetation units recognized for a particular site unit are arranged according to site history and successional status.
In order to arrange ecosystems at the three levels of integration, the BEC system combines four classifications: vegetation, climatic (zonal), site, and seral. Vegetation classification is most important to developing the ecosystem classification. However, the climatic and site classifications are the principal classifications used in the application of the BEC system. At this time the seral classification has not been adequately developed.