Taiga Shield High Subarctic Ecoregion

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Overview

The Taiga Shield High Subarctic (HS) Ecoregion arcs across the northern third of the Taiga Shield. Landscapes are dominated by bedrock and discontinuous permafrost in the western half, and bouldery till blankets and sandy to gravelly outwash further east. Open spruce woodlands and polygonal peat plateaus are typical upland and wetland vegetation types.

General Description

The Level III Taiga Shield HS Ecoregion occupies the northern third of the Taiga Shield within the Northwest Territories; it is over 900 km from northwest to southeast and includes nine Level IV ecoregions. Its northern boundary with the Level II Southern Arctic Ecoregion approximates the tree line. Tundra cover on hilltops and islands, and nearly treeless polygonal peat plateaus distinguish this ecoregion from the Taiga Shield LS Ecoregion to the south. Landforms range from bouldery till plains and uplands in eastern parts of the Ecoregion to till veneers and fractured bedrock further west; outwash plains and eskers are common throughout. Open spruce woodlands on lower slopes and valleys, shrub tundra communities on upper slopes and hilltops and scattered polygonal peat plateaus and sedge marshes in low wet areas are common vegetation types.

Climate

There are no permanent, long-term climate data collection stations in the Taiga Shield HS Ecoregion. The climate is characterized as High Subarctic by the Ecoregions Working Group (1989) and Bradley et al. (1982) Polygonal peat plateaus are the dominant wetland form, nonsorted circles and patterned ground become common near the northern boundary, and increasingly suppressed tree growth to the north reflects a progressively shorter growing season, less available photosynthetic energy and more xeric soil moisture conditions (Timoney et al. 1993). Climatic statistics have been modelled over large areas using limited data from other areas; climate models at the ecodistrict level for that portion of the Taiga Shield within the Northwest Territories (Agriculture and Agri-Food Canada 1997) provide the following general statistics. The mean annual temperature ranges from –4 to –9ºC. The mean temperature in January, the coldest month, ranges from –27 to –30ºC, and from 13 to 16ºC in July, the warmest month. Mean annual precipitation is between 270 and 390 mm, with the wettest period in June through September; about 60 percent falls as rain and 40 percent as snow. The models indicate that conditions become colder and drier from southeast to northwest across the Ecoregion. The mean annual daily solar input (refer to Section 1.4.1 for further explanation) ranges between 10 and 11mJ/m²/day, with low values of 0.6 to 1.1 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 HS Ecoregion is a complex of till plains and Precambrian bedrock outcrops. The Ecoregion reaches maximum elevations of over 500 m in the northwest, decreasing to elevations of less than 200 m in the Thelon Valley. Although local variations are generally less than 100 m, the terrain can be rugged in bedrock-dominated areas. Granitoid, intrusive and metamorphic bedrock plains and hills characterize the northwest third of the Ecoregion. Coarse-textured till veneers with bedrock outcrops occur in the central third; drumlinized and fluted, generally bouldery till plains with scattered bedrock outcrops are typical of the southeastern third. Outwash plains and esker complexes are common throughout the Ecoregion. Peatlands cover less than five percent of the Ecoregion, but numerous lakes occupy nearly a quarter of the total area. Permafrost is continuous along the northern boundary and discontinuous elsewhere. Soils are dominantly Brunisols (unfrozen) and Turbic Cryosols (perennially frozen, affected by cryoturbation. Minor occurrences of Organic Cryosols are associated with wetlands.

Vegetation

Tree line is determined by the interaction of climatic factors and local site conditions. Black spruce is less tolerant of cold climates than white spruce, but it is more tolerant of nutrient-poor conditions (Timoney 1995). Tree line plunges steeply southward across the Taiga Shield HS in response to the prevalence of nutrient-poor sandy parent materials, and the dominant tree species on poor sites is black spruce. At tree line, trees are restricted to sheltered locales and well-drained soils. Climatic variations over decades influence conifer seed production and seedling survival; vegetative reproduction and the shelter of established tree stands allow trees to persist or increase during unfavourable periods (Szeicz and MacDonald 1995). South of tree line, open, stunted spruce woodlands with lichen and shrub understories are typical of lower slopes and valleys; shrub and lichen tundra communities occupy upper slope and crest positions. Rock barrens account for a significant area in the northwest portion of the Ecoregion. Fires in the southern third of the Ecoregion have produced extensive areas of regenerating dwarf birch. Jack pine is absent from this Ecoregion, and trembling aspen occurs only as stunted individuals on south-facing slopes. Appendix 2 summarizes the major plant community types.

Ecoregions

The following are the smaller ecoregions within the Taiga Shield High Subarctic Ecoregion:

Radium Hills HS Ecoregion Coppermine Upland HS Ecoregion Point Upland HS Ecoregion Snare Plain HS Ecoregion Mackay Upland HS Ecoregion Thelon Valley HS Ecoregion Whitefish Plain HS Ecoregion Sid Plain HS Ecoregion Dubawnt Plain HS Ecoregion

Click here for more information on the Taiga Shield High Subarctic Ecoregion and all of the ecoregions within it.