Ecoregion Classification Background
British Columbia's Environment - The Setting
The British Columbia Ecoregion Classification
Ecoregion Classification System Hierarchy
Uses of the British Columbia Ecosystem Classification
British Columbia's Environment - The Setting
British Columbia has many ecosystems due to its varied physiography and climates. It is located at mid- to northerly latitudes and is bounded on the west by oceanic influences of the northern Pacific Ocean and on the east by continental climates of the Interior Plains and Rocky Mountains. Its varied geological history has resulted in a complex topography. In addition, the province has had a complex climatic history. Current climatic patterns are varied but, most typically, the province is dominated by moist, cool to cold, temperate climates in a mountainous setting, most of which is higher than 1,000 m above sea level. The plants and animals of the province are affected by that environment and also by historic factors such as position of glacial refugia or barriers to dispersal and migration.
The combined influence of differential heating of land and ocean masses and the spin of the earth has created a general circulation in the earth's atmosphere (Thompson 1981). That circulation is separated into a number of latitudinal belts, one being the prevailing westerly winds that influence British Columbia and most of southern Canada and the northern contiguous United States (Marsh 1988). Because of the prevailing winds, the general movement of the upper air is from west to east. Low and high pressure areas move across north-central North America embedded in the westerlies stream. Their movement is also associated with an interaction between southward flowing cold air and northward flowing warm air. In winter, cold, high pressure areas dominate the interior of the continent and relatively warm, low pressure areas dominated the coastal areas. In summer the pattern is reversed with large semi-permanent high pressure area over the northeastern Pacific dominating the general circulation in western Canada. These circulating patterns create 14 distinct regional climates.
The rugged relief of the western cordillera has a great effect on the climate of western Canada, northern Washington, and the panhandle of Alaska. The Coast Mountains limit the mild, humid Pacific air to a narrow band along the coast. As the prevailing eastward-moving air is forced to rise over successive mountain ranges, precipitation occurs on windward slopes. The Rocky Mountains commonly block westward-moving outbreaks of cold Arctic air. Southward-moving Arctic air from the Yukon and northern British Columbia is impeded by the Coast Mountains and so flows into the interior of the province. During warm months, hot, dry air from the Great Basin of the United States occasionally moves into the southern interior plateau area from the southeast, bringing clear skies and hot temperatures.
Most of British Columbia is comprised of a series of land masses (terranes) that have collided with western North America during the past 190 million years (Gabrielse et al. 1991; Mathews and Monger 2005; Yorath 1990). The two major accretion events that have occurred have caused uplift and distortion of the original continental margin. These events are still happening as the last portion of the ocean plate disappears under the continent. By using these geological events, the province can be subdivided into several major physiographic units. The oldest portion of the North American continent in the province, the northeastern plain, is a relatively flat plateau - the remnant of a great inland sea. West and southward, the former continental margin has been uplifted and distorted to form the Rocky and eastern Columbia Mountains. In the centre of the province, the interior mountains and plateaus are composed of four large terranes and several smaller ones that form a superterrane that docked against the continent distorting the continental margin into the Rocky and Columbia mountains. The coastal mountains, islands, and continental shelves are composed of two large terranes and several smaller ones that docked as a second super terrane against the first. Intensive heating of basement rocks has resulted in a belt of extensive granitic intrusion. The western-most portion of British Columbia is a deep-water, oceanic sea - the continental rise. That physiographic area consists of gentle slopes overlain by an apron of thick sediments.
Within the past two million years, five successive periods of continental glaciation, followed by warm periods, have occurred over British Columbia. The result has been a reshaping of the landforms and deposition of surface materials. Since the waning of the continental ice sheets 12,000 to 15,000 years ago, there have been several climatic fluctuations in the province (Clague 1989; Fulton 1989; Pielou 1991). As recently as a few hundred years ago, there was a short period of cordilleran ice build-up; however, the current climatic trend in British Columbia as we enter an era of global warming caused by the buildup of "green house" gasses possibly is for warmer and widely fluctuating climates.
The vegetation of British Columbia reflects the climatic and physiographic differences both provincially and regionally. Marked vegetation belts are a striking feature of regional vegetation (Krajina 1965; Meidinger and Pojar 1991). On the coast, the natural vegetation is needle-leaf forests of Douglas-fir, western redcedar, western hemlock, Sitka spruce, amabilis fir and yellow-cedar. These are some of the densest of all coniferous forests and hold some of the world's largest trees. On the upper mountain slopes lies a narrow subalpine belt of mountain hemlock and amabilis fir forests. Rugged, moist alpine is common at the higher elevations and relict glaciers dominate much of the high Pacific and Boundary ranges. In the Southern Interior, steppe vegetation dominates the major valleys and basins. Sagebrush, ponderosa pine, or Douglas-fir are common throughout. However, an increase in elevation prolongs the winter season enabling Douglas-fir, lodgepole pine, Engelmann spruce, and subalpine fir forests to become established. In the central interior and southeastern mountains at the lower levels is a montane belt of Douglas-fir and lodgepole pine forests, whereas western hemlock and western red cedar are characteristic where moisture is greatly increased. Above is the subalpine belt, dominated in most places by Engelmann spruce and subalpine fir or lodgepole pine forests. The uppermost vegetation belt is the alpine; quite often relict glaciers are present on the highest portions. In the Sub-Boreal Interior, the Sub-Boreal Pine-Spruce zone has forests of lodgepole pine with some white spruce, which are characteristic in the southern portion. In the northern portions, the Sub- Boreal Spruce zone forests of lodgepole pine, hybrid spruce, and subalpine fir are common. In the cold northern mountains, vertical vegetation is characterized by muskeg and black spruce in the low lying, poorly drained areas, or willow-birch shrublands in the low valleys where cold air frequently pools. White spruce, lodgepole pine, subalpine fir, and occasionally trembling aspen occur on the midslopes. Alpine grasslands dominate most rounded summits while barren rock or mat-vegetation occur on the highest summits. On the Alberta Plateau, white and black spruce and lodgepole pine forests are dominant. Some poorly drained areas have muskeg with black spruce and tamarack, the lower basins and riverbreak areas have shrub rich grasslands intermixed with aspen. In the Fort Nelson Lowlands, extensive wetlands and muskeg occur over much of the area because it is so poorly drained, although the better drained upland areas have well developed boreal forests.
Western Canada’s oceanic environment is dominated by the Subarctic Current which has moved eastward across the breadth of the northern Pacific Ocean. In the Subarctic Pacific Region that current divides into a counterclockwise flowing Alaska Current and a clockwise flowing California Current. Those currents meet the continental shelf currents and the freshwater discharges of British Columbia's rivers to form estuarine conditions for most of the coastal areas. Inland many fjords and glacial scoured inter-island channels dominate the marine environment (Thomson 1981)."Western Canada’s oceanic environment is dominated by the Subarctic Current which has moved eastward across the breadth of the northern Pacific Ocean. In the Subarctic Pacific Region that current divides into a counterclockwise flowing Alaska Current and a clockwise flowing California Current. Those currents meet the continental shelf currents and the freshwater discharges of British Columbia's rivers to form estuarine conditions for most of the coastal areas. Inland many fjords and glacial scoured inter-island channels dominate the marine environment" (Thomson 1981).
The Ecoregions of British Columbia
The British Columbia Ecoregion Classification
The understanding of British Columbia’s complex environment is essential for the management, utilization, and conservation of the province’s natural resources. The purpose of a regional ecosystem classification scheme is to organize the ecological mosaic into simple patterns and to provide a practical framework for managing natural resources (Bailey and Hogg 1986). Several regional classification schemes exist for the stratification of parts of North America into ecosystem units (see; Munro and Cowan 1947; Krajina 1965; Omernik 1977; Bailey 1995; Brown and Lowe 1980; Brown 1982: Wiken 1986; Gallant et al. 1989; Hirvonen et al. 1995; McNab and Avers 1994; Ecological Stratification Working Group 1995). Each has its positive attributes, but each also has shortcomings for delineating regional ecosystems in a mountainous area such as British Columbia.
The British Columbia Ecoregion classification was developed to provide a systematic view of the small scale ecological relationships in the Province given its great ecological complexity (Demarchi 1988; Demarchi et al. 1990). This classification is based on macroclimatic processes (Marsh 1988), and physiography (Holland 1964; Mathews 1986), which is a fundamental difference between this and all other regional ecosystem classifications. Macroclimatic processes are the physical and thermodynamic interaction between climatic controls, or the relatively permanent atmospheric and geographic factors that govern the general nature of specific climates.
Another concept that is unique to the British Columbia Ecoregion classification is the integration of the terrestrial and marine environments so as to describe one regional ecosystem classification. The stratification of the B.C. marine and oceanic environments into Ecoregions was first proposed by Demarchi et al. (1990), subsequently a National Marine Ecoregion classification was developed, with many of the same units as the B.C. Ecoregion classification (Hirvonen et al. 1995; Zacharias et al. 1998).
There is also another level of ecological complexity that occurs within mountainous regions, that of topo-climatic zonation. Within each terrestrial region bounded by climatic processes and landform parameters, there are climatic zones that are reflected by the plant and animal communities present. This level is best pursued through the Biogeoclimatic Ecosystem Classification (British Columbia Ministry of Forests 2003; Krajina 1965; Meidinger and Pojar 1991). At the biogeoclimatic subzone level, the climate interacts with land surface materials to create particular environments suitable for the development of specific plant and animal communities (Rowe 1984; Demarchi and Lea 1987). Oceanic Environments, however, are the products of temperature, salinity, sea-bed configuration, and water depth (Thomson 1981). Classification of marine biophysical zonation is best pursued through the British Columbia Marine Ecosystem Classification (Zacharias et al. 1998) and the report on the Oceanography of British Columbia (Thomson 1981).
The Ecoregion classification system of British Columbia divides the province into 208 units. However, arranging them into a hierarchical classification simplifies the result and makes them a useful tool for managing the natural resources of the province. The hierarchical levels has been defined as follows:
an area of broad climatic uniformity, defined at the global level (4 units);
an area of broad climatic and physiographic uniformity, defined at the continental level (7 units);
an area with consistent climatic processes or oceanography, and relief, defined at the sub-continental level (11 units);
an area with major physiographic and minor macroclimatic or oceanographic variation, defined at the regional level (47 Units);
an area with minor physiographic and macroclimatic or oceanographic variation, defined at the sub-regional level (139 Units).
The Ecodomains and Ecodivisions are very broad and place British Columbia in a global context. Ecoprovinces, Ecoregions, and Ecosections are progressively more detailed and narrow in their scope and relate the province to other parts of North America or the Pacific Ocean, or segments of the province to each other. These lower three classes describe areas of similar climate, physiography, vegetation, and wildlife potential. In the terrestrial environment each Ecoregion or Ecosection class can be further subdivided by biogeoclimatic criteria to provide a basis for detailed interpretation of climate, topography, soil, and vegetation for the purposes of habitat and wildlife management. And in the marine environment each Ecoregion or Ecosection can be subdivided by biophysical criteria to provide a detailed interpretation of climate, bathymetry, water chemistry, and currents for the purposes of fisheries management.
Since the first Ecoregions of British Columbia map was prepared in 1988 (Demarchi 1988) there have been a number of edits, corrections and changes, in fact as predicted by Demarchi et al. (1990) as a better understanding of the broad ecological relationships in the province is gathered by such means as mapping ecosystems in greater detail, the Ecoregions map will continue to be updated. The first Ecoregion map was based on 1:2,000,000 level macroclimatic, physiographic and geographical information. By 1993 the Ecoregion classification became integrated with the Biogeoclimatic Ecosystem Classification as was mapped at 1:250,000. In 1995, the Ecoregion classification was edited using the revised - 1995 Biogeoclimatic mapping, in addition a number of changes suggested from mapping exercises coordinated by the Ecological Stratification Working Group (1995), and mapping the British Columbia Ecoregion Classification criteria into the United States (Demarchi 1994a; Demarchi et al. 2000) were incorporated into the British Columbia Ecoregion map. In the mid-1990’s five cooperative ecoregional mapping projects with the province and adjacent jurisdictions resulted in a better coordination of Ecoregion units that British Columbia had in common with Alberta and the Northwest Territories (Ecological Stratification Working Group 1995); with the Yukon (Smith et al. 2004); Alaska (Nowacki et al. 2001); and with Montana, Idaho and Washington (Demarchi 1994; Demarchi et al. 2000). In 2003 after working on a province-wide wildlife habitat capability mapping project with regional staff in the Ministry of Environment subtle variations to the Ecosection units were proposed and changed. And in 2009 with new Biogeoclimatic zonation mapping at a scale of 1:20,000, further refinement of all Ecoregion units and boundaries became evident, subsequently a few new Ecosections were delineated.
While the central concept of the British Columbia Ecoregion classification remains the same, there has been a redefinition of all the boundaries. One new Ecoprovince has been identified giving the total now to 11 from 10. The number of Ecoregion units has increased from 30 in 1988, to 34 in 1991, to 43 in 1993, to 47 in 1995, it remains at 47 now in 2011. The numbers of Ecosections, have seen the most increases going from 78 in 1988, to 87 in 1991, to 110 in 1993, to 116 in 1995, to 139 at present. Further modifications may occur as a result of coordination with other jurisdictions as has happened in the past.
The effect of global climate change on the provincial Ecoregion units – as the base concept for mapping Ecoregions in British Columbia has always been the underlying principal of units defined by variation caused by the interaction climatic processes (how we get our weather) and the landforms of the province, it is not expected that changes to global climates will change either of those two. Therefore the Ecoregion units are not likely to change in any appreciable way. However, there will be substantial changes to the climatic parameters that underlie the basic principles of the Biogeoclimatic Classification, such things as growing-degree days, mean July and mean January temperatures and precipitation amounts will all change, resulting in shifting boundaries and either additional or grouping of Biogeoclimatic units. So that the changing climate will change the Biogeoclimatic unit definitions and boundaries and that will affect the placement of the Ecoregion unit boundaries, but the central concepts for each Ecoregion unit will remain the same.
Uses of the British Columbia Ecosystem Classification
The value of an Ecoregion classification to resource managers is that it will place any ecosystem in a local, regional, provincial, continental or global context, and therefore provide a framework for the understanding of what are often complex, interacting systems. The merits of the Ecoregion classification to recreationalists and the general public is that they can become more aware of the Province’s environment, and may understand which areas of the Province contain unique ecosystems, and which ecosystems are connected to other jurisdictions.
Since its first publication in Volume 1 of the “Birds of British Columbia” (Campbell et al. 1990; Demarchi et al. 1990), the Ecoregion Classification for British Columbia has become widely accepted as the standard classification for describing regional ecosystems within the province, just as the Biogeoclimatic Ecosystem Classification is the standard classification for describing zonal ecosystems within B. C. (Meidinger and Pojar 1991). As Demarchi (1994 a, b) and Mah et al. (1996) have outlined, land use and conservation goals are set at provincial or regional levels using information that has been based on broad scale physiography, climate and vegetation (e.g. Ecoregions and Biogeoclimatic Zones). This information has been used by government resource agencies for provincial and regional land use planning, especially for the Protected Areas Strategy (Lewis and MacKinnon 1992; Province of British Columbia 1993; Demarchi 1994a), and as a standard against which biological data can be assessed (see Campbell et al. 1990; British Columbia Wildlife Branch 1991; Province of British Columbia 1993).
The British Columbia Ecoregion Classification has also been used as a means of understanding our regional ecosystems and resource management concerns in relation to those of our adjacent neighbours in Canada and the United States. The Ecoregions of Canada (Ecological Stratification Working Group 1995) is one example in which the British Columbia Ecoregion level is used for National State of the Environment Reporting. In addition carnivore management specialists in American states adjacent to the south of the province have relied on the British Columbia Ecoregion classification to map regional ecosystems from British Columbia into the western United States (Demarchi 1994a), and eastern Washington, Northern Idaho, northwestern Montana, and southwestern Alberta (Demarchi et al. 2000).