2.2 Biogeoclimatic Units

The biogeoclimatic ecosystem classification (BEC) is a hierarchical classification scheme that includes separate zonal (climatic) and site classifications. Meidinger and Pojar (1991) and Pojar et al. (1987) describe the system in detail. Biogeoclimatic units represent geographic areas under the influence of the same regional climate. The biogeoclimatic subzone is the basic unit. Subzones are then grouped into zones and divided into variants and phases, reflecting similarities and differences in regional climate.

A biogeoclimatic subzone consists of unique sequences of geographically related ecosystems. Its climatic climax ecosystems are members of the same zonal plant association. Such sequences are influenced by one type of regional climate. To date, about 100 subzones are recognized in British Columbia (Meidinger and Pojar, 1991).

Subzones with similar climatic characteristics and zonal ecosystems are grouped into biogeoclimatic zones. A zone is a large geographic area with a broadly homogeneous macroclimate. Fourteen biogeoclimatic zones are recognized in British Columbia (Meidinger and Pojar, 1991).

Subzones contain considerable variation and can be divided into biogeoclimatic variants, which reflect further differences in regional climate. Variants are generally recognized for areas that are slightly drier, wetter, snowier, warmer, or colder than other areas in the subzone. These climatic differences result in corresponding differences in vegetation, soil, and ecosystem productivity. The differences in vegetation are evident as a specific climax plant subassociation on zonal sites.

In the regional climate of subzones and variants, biogeoclimatic phase accommodates the variation resulting from local relief. Phases are useful in designating significant areas that are, for topographic or topo-edaphic reasons, atypical for the regional climate. Examples could be extensive areas of grassland occurring only on steep, south-facing slopes in an otherwise forested subzone, or valley-bottom, frost-pocket areas in mountainous terrain. To date, only a few phases are recognized in the province.

Biogeoclimatic subzones and variants are the units mainly used in TEM. Phases are mapped when present. British Columbia is mapped to the biogeoclimatic zone level at 1:2 000 000 and at the subzone/variant level for all forest regions at scales ranging from 1:100 000 to 1:500 000.

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