Taiga Shield High Boreal Ecoregion
Overview
The Taiga Shield High Boreal (HB) Ecoregion occupies the eastern third of the Taiga Shield; it is bedrock-dominated with jack pine and mixed spruce forests on rock outcrops, thin bouldery till, and outwash.
General Description
The Level III Taiga Shield HB Ecoregion extends south from 64º N latitude to the Alberta – Northwest Territories border, a distance of about 650 km, and includes five Level IV ecoregions. North of Great Slave Lake, the Ecoregion is about 80 to 100 km wide from its western boundary with the Level II Taiga Plains Ecoregion to its eastern boundary with the Level III Taiga Shield LS Ecoregion, and occurs at elevations of 300 mASL or less. South of Great Slave Lake, the Ecoregion is about 150 to 200 km wide; the land rises gently to the east and reaches elevations of over 500 mASL in the southeast corner. Exposed bedrock plains and undulating to hilly bedrock uplands are the dominant landscape feature, with thin bouldery till veneers mainly in the lowland areas between Great Slave Lake and Great Bear Lake. Jack pine stands occupy large areas with high fire frequency; black spruce – shrub – lichen stands are dominant where fires are less frequent. White spruce and trembling aspen forests are common in low-elevation areas to the west where nutrient and water supplies are adequate. Peat plateaus and shore and floating fens are scattered throughout.
Climate
Yellowknife is the only station from which climate data have been collected over long periods within the Taiga Shield HB Ecoregion, and climate statistics are therefore determined through interpolated models using the limited available data. The extensive occurrence of jack pine, the development of mixed-wood stands along the western third of the Ecoregion, the absence of polygonal peat plateaus and the presence of more extensive shoreline and aquatic vegetation communities provides supporting evidence for comparatively warm conditions. Climate models (Agriculture and Agri-Food Canada 1997) provide the following general statistics. The mean annual temperature ranges from –3 to –6ºC. The mean temperature in January, the coldest month, ranges from –26 to –28ºC, and from 15 to 16ºC in July, the warmest month. Mean annual precipitation is between 280 and 360 mm, with the wettest period in June through November; about 50 percent falls as rain and 50 percent as snow. The mean annual daily solar input (refer to Section 1.4.1 for further explanation) ranges between 10.5 and 11.0 mJ/m2/day, with low values of 1.0 to 1.5 mJ/m2/day in December and highs of 21.5 to 22.0 mJ/m2/day in June.
Topography, Geology, Soils, and Hydrology
South of Great Slave Lake, the land rises from about 200 mASL along the western boundary to over 500 mASL in the southeast corner. North of Great Slave Lake, elevations range from about 100 mASL to 300 mASL. Nearly level to rolling and hilly Precambrian granitoid, intrusive and metamorphic crystalline bedrock is the dominant landform, with thin bouldery coarse-textured till veneers over much of the area and somewhat deeper till deposits in the southeast. Eskers and outwash deposits occur mainly in the southeast on higher terrain and are not widespread elsewhere. Fine-textured, relatively nutrient-rich lacustrine deposits have accumulated in low-lying areas between bedrock exposures at lower elevations along the west side of the Ecoregion. Brunisols are the most common soils, with Regosols and Gleysols near streams and lakes. Peatlands cover less than five percent of the Ecoregion, but lakes account for nearly one-third of the area, and Great Slave Lake is the largest water body.
Vegetation
Bradley et al. (1982) describe two major upland vegetation types associated with bedrock and discontinuous glacial deposits in the High Boreal ecoclimatic region on the Taiga Shield – lichen woodland and moss forest. Lichen woodland/rock lichen woodland with jack pine, black spruce and paper birch occurs on thin soils over bedrock, in bedrock fractures and on well-drained coarse-textured outwash deposits. Moss forest, typically with a moderately dense black spruce canopy that favours the development of a feathermoss understory, occurs on deeper, moister soils; mixed or pure forests of white spruce, trembling aspen and paper birch also occur on moderately moist sites. Fire has had a major influence on the Taiga Shield HB Ecoregion. Large expanses are forested with closed canopy conifers and young jack pine and paper birch stands. Black spruce stands occur on areas that have longer fire-return intervals; stand size is determined by the extent and depth of till deposits on bedrock. Mixed-wood stands of white spruce and aspen are common on lacustrine and fluvial materials in the low-elevation areas. Rock lichen communities colonize bare bedrock and include several species of lichens and a few dryland mosses. Black spruce and jack pine occur in shallow depressions or in fractures that hold water and together with lichens and low shrubs form sparsely treed rock lichen woodland. The bright green hues of shoreline and floating fens and the abundance of variegated pond lily colonies in shallow water are characteristic of this Ecoregion. Appendix 2 summarizes the major plant community types.
Ecoregions
The following are the smaller ecoregions within the Taiga Shield High Boreal Ecoregion:
|
Great Slave Upland HB Ecoregion
Great Slave Lowland HB Ecoregion
East Arm Upland HB Ecoregion
Rutledge Upland HB Ecoregion
Nonacho Upland HB Ecoregion
|
 |
Click here for more information on the Taiga Shield High Boreal Ecoregion and all of the ecoregions within it.
|
Total area: 84,767 km2 (26% of Taiga Shield).
|