Taiga Shield Low Subarctic Ecoregion
Overview
The Taiga Shield Low Subarctic (LS) Ecoregion extends from northwest to southeast in a broad band across the Taiga Shield. Level to rolling and hilly bedrock with thin bouldery till veneers, open black spruce stands and large burned areas are characteristic landscapes.
General Description
The Level III Taiga Shield LS Ecoregion spans over 1000 km, extending from the northwestern to southeastern borders of the Taiga Shield within the Northwest Territories. It is more than 200 km wide at its northwest and southeast limits, but has an average width of about 80 km in the central portion and is only 20 km wide at it narrowest point. It includes ten Level IV ecoregions. Toward its northern boundary, polygonal peat plateaus become more common and are indicative of cold climates that are transitional between Low Subarctic and High Subarctic. Tundra replaces forest cover on hilltops and on islands in lakes, also denoting colder climates. Along its southern boundary with the Taiga Shield HB Ecoregion, shore fens along lakeshores and jack pine stands become more extensive. Most of the Ecoregion north of Great Slave Lake is comprised of exposed bedrock with discontinuous bouldery coarse-textured till veneers. Deeper bouldery till blankets are more common south of Great Slave Lake. Coarse-textured outwash deposits occur throughout the Ecoregion. On the deeper till deposits, black spruce – lichen woodlands and extensive post-fire regenerating stands of paper birch and dwarf birch are characteristic. North of Great Slave Lake, thin soils or exposed bedrock limit the development of forests, and outwash plains, bedrock fractures and thin till veneers support discontinuous black spruce stands.
Climate
Fort Reliance is the only station from which climate data have been collected over long periods within the Taiga Shield LS Ecoregion, and climate statistics are therefore determined through interpolated models using the limited available data. Peat plateaus and slow-growing open conifer stands across most of the region are indicative of a Low Subarctic climate, as defined by the Ecoregions Working Group (1989) and Bradley et al. (1982). Climate models (Agriculture and Agri-Food Canada 1997) provide the following general statistics for the Taiga Shield within the Northwest Territories. The mean annual temperature ranges from –3.5 to –9.0ºC. The mean temperature in January, the coldest month, ranges from –27 to –29.0ºC, and from 11.0 to 16.0ºC in July, the warmest month. Mean annual precipitation is between 230 and 430 mm, with the wettest period in June through October; about 60 percent falls as rain and 40 percent as snow. The models indicate that climates become colder and drier towards the northwest, with the highest precipitation predicted for the Abitau Upland, a high-elevation area along the Northwest Territories – Saskatchewan border. The mean annual daily solar input (refer to Section 1.4.1 for further explanation) ranges between 10 and 11 mJ/m2/day, with low values of 0.8 to 1.4 mJ/m2/day in December and highs of 21.5 to 22 mJ/m2/day in June.
Topography, Geology, Soils, and Hydrology
The Taiga Shield LS Ecoregion is characterized by thin, discontinuous till veneers and blankets overlying complex Precambrian intrusive, granitoid and sedimentary rocks north of Great Slave Lake, and by deeper till deposits overlying Precambrian metamorphic, sedimentary and intrusive bedrock south of Great Slave Lake. Drumlin fields are extensive and conspicuous landforms in the southeastern portion of the Ecoregion. Peatlands cover between five and 10 percent of the total area, and the most extensive occurrence is in the southeast, where nearly treeless polygonal peat plateaus are common. Soils are mainly Brunisols on uplands and Organic Cryosols in peatlands. About 25 percent of the total area is covered by water, mostly as lakes less than 500 ha; the East Arm of Great Slave Lake and Hottah Lake are the two largest water bodies.
Vegetation
South of Great Slave Lake where till deposits are relatively deep, open black spruce stands with a shrubby understory of dwarf birch, northern and common Labrador tea and lichens are the primary upland vegetation type on areas that have not recently burned. Dwarf birch – spruce stands are extensive on recently burned areas, with jack pine on coarse-textured materials as far north as 64o N latitude. North of Great Slave Lake, black spruce – lichen forests occur in discontinuous patches between rock exposures, with rock lichen communities on bedrock exposures. Bogs, collapse scar fens and nearly treeless lichen – Labrador tea – Sphagnum moss communities occur in association with permafrost features such as peat plateaus and polygonal peat plateaus. Shore fens (floating wetlands along lakeshores) are more common in the northwest part of the Ecoregion than elsewhere. Appendix 2 summarizes the major plant community types.
Ecoregions
The following are the smaller ecoregions within the Taiga Shield Low Subarctic Ecoregion:
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Radium Hills LS Ecoregion
Calder Upland LS Ecoregion
Camsell Plain LS Ecoregion
Great Slave Upland LS Ecoregion
East Arm Upland LS Ecoregion
Porter Upland LS Ecoregion
Wignes Plain LS Ecoregion
Abitau Upland LS Ecoregion
Dubawnt Plain LS Ecoregion
Selwyn Upland LS Ecoregion
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Click here for more information on the Taiga Shield Low Subarctic Ecoregion and all of the ecoregions within it.
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Total area: 114,414 km2 (35% of Taiga Shield).
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