Broadly speaking, British Columbia is a cool, moist, mountainous, forested province. However, the province also has areas with Mediterranean-type, semi-arid, subarctic and alpine climates. It has extensive plateaus, plains and basins as well as several roughly parallel series of mountains. All nine main groups of soils found in Canada occur in British Columbia. Forests dominate the vegetation but areas of grasslands, wetlands, scrub and tundra are extensive. Species diversity is high for all known groups of organisms.
This chapter provides a broad overview of B.C.’s forested and non-forested ecosystems.[2] It describes the province’s physiography, climate, soil and vegetation and introduces the biogeoclimatic ecosystem classification system on which forest management decision-making is based.
British Columbia can be separated into five physiographic regions: the Coast Mountains and Islands, Interior Plateau, Columbia Mountains and Southern Rockies, Northern and Central Plateaus and Mountains, and Great Plains (3]
The wettest climates of British Columbia (and Canada) occur along B.C.’s coastline, especially near the mountains on windward slopes of Vancouver Island, the Queen Charlotte Islands and the mainland Coast Mountains. Here, moist air carried by prevailing westerly winds drops large amounts of rain or snow as it is forced up the mountain slopes. The air descends over the eastern slopes and is warmed by compression, causing the clouds to thin out. The pronounced rainshadow cast by the massive Coast Mountains results in the driest climates of British Columbia, located in valley bottoms of the south-central Interior. The air releases additional moisture as it again ascends the Columbia, Skeena, Omineca and Cassiar mountains and finally the Rocky Mountains.
Mountains not only impede eastward-moving air masses, they also restrict the westward flow of cold, continental Arctic air masses from east of the Rocky Mountains. Thus, except for the unprotected Great Plains region of the northeast, British Columbia has a more moderate winter climate than does the vast central part of Canada.
The prevailing westerlies weaken during the summer. The summer climate is controlled by a large, semi-permanent high pressure centre in the Pacific, which greatly reduces the frequency and intensity of Pacific storms. The Interior in spring has little precipitation, though early summer is often relatively wet. By mid-summer, however, interior storms and precipitation decline again. In middle and late summer the “Pacific high” often exerts dominance over western North America, giving warm, clear weather to much of British Columbia.
Many kinds of soil have developed throughout British Columbia as a result of different intensities of soil-forming processes, including the interaction of parent material, climate, biota, topography and time. Nine major groups of soils (soil orders) occur in British Columbia.[6]
Brunisolic soils occur primarily in forested areas, where relatively low rates of weathering have limited the development from the original parent material. The slow weathering and/or restricted development may be due to climate (long winters and low temperatures in cold climates, lack of soil moisture in dry climates), the coarse texture of parent materials or the geological youth of recently deposited parent material.
Dark, fertile Chernozemic soils have formed primarily under grasslands in the warm, dry, south-central Interior. Chernozems are typical of areas where low rainfall, high summer temperatures and high rates of evapotranspiration inhibit tree growth, limit soil leaching and lead to the accumulation of organic matter in the topsoil.
Cryosolic soils contain permafrost and occur as mineral soils at high elevations and as organic soils in the peat bogs of northern B.C. Low soil temperatures inhibit chemical reactions and microbial activity, but physical weathering is active.
Gleysolic soils are saturated for long periods of the year, and their profiles show evidence of the activity of anaerobic bacteria. Gleysols occur throughout the province wherever water does not drain away as quickly as it is added to the soil. Gleysols dominate where water tables are high in the lower Fraser Valley and are widespread over some of the large flat plains of northern B.C. Elsewhere, they occupy depressions on plateaus or lower, moisture-receiving slope positions in mountainous terrain.
Luvisolic soils are characterized by a zone or horizon of clay accumulation in the subsoil as a result of leaching from above. This clay-rich horizon may restrict penetration by roots, air and water. Luvisols have formed under forest cover in areas which have either higher rainfall, lower temperatures with less evapotranspiration or finer-textured parent materials than areas dominated by Brunisolic or Chernozemic soils. Luvisolic soils cover much of the Interior Plateau and a large part of the Great Plains.
Organic soils consist mainly of organic matter and develop mostly under saturated conditions, where dead vegetation accumulates faster than it decomposes. Organic soils typically occupy poorly drained depressions and support wetland vegetation; they can also develop on sloping terrain in very wet climates. Unlike organic soils, Folisols (a sub-group of organic soils) are not composed dominantly of mosses, sedges and other aquatic plants. They are formed under upland forest conditions, are freely drained; they are commonly found on the north Coast and in coastal subalpine forests. Organic soils dominate the landscape along the north Coast and in parts of the Great Plains.
Podzolic soils generally form under coniferous forest in temperate and wet or in cold and moist climates. Podzols are typically well drained and coarse textured and undergo intense leaching of clay, organic matter, iron and aluminum from upper to lower mineral horizons. Podzols dominate most of the coastal region, the interior wet belt and the mountain systems of British Columbia.
Regosolic soils are very weakly developed and often very shallow, although some may have significant accumulations of organic matter in the surface layer. Regosolic parent materials are only slightly modified, because they are recent (as on flood plains or beaches), unstable (as on eroding slopes) or in harsh environments where rates of chemical weathering and microbial activity are very low. Regosols do not cover extensive areas of British Columbia except in high mountains.
Solonetzic soils contain high amounts of exchangeable sodium or sodium and magnesium salts in the subsoil. The salts cause the soil to become sticky and massive when wet and very hard and blocky when dry. The high salt content limits plant growth, and in some cases only salt-tolerant plants survive. Solonetzic soils are common in dry parts of the southern Interior, but are restricted to poorly drained depressions. In these areas, soil water drains into depressions and evaporates, leaving an accumulation of salts. In the Peace River district of northeastern B.C., where saline soils are widespread in some areas, the salts originate in saline marine bedrock.
