This ecoregion extends over 450 km eastward from James Bay in northern Quebec, between the Grande rivière de la Baleine in the north and the rivière Eastmain to the south. It is marked by cool summers and very cold winters. The mean annual temperature is approximately -4°C. The mean summer temperature is 8.5°C and the mean winter temperature is -16.5°C. The mean annual precipitation ranges from less than 600 mm along Hudson Bay to 800 mm in the southeast. The ecoregion is classified as having a low subarctic ecoclimate. Its open coniferous forests are transitional to tundra and alpine tundra vegetative communities to the north and the closed cover of typical coniferous boreal forests to the south. Open stands of lichen-black/white spruce woodland with an understory of feathermoss are dominant. Black spruce is the climax species. Less rugged than Lake Plateau to the east, the southern section of Larch Plateau has a hummocky surface with elevations ranging from 150 m asl near the coast to 450 m asl in the vicinity of the Caniapiscau Reservoir in the east. This ecoregion is composed predominantly of massive Archean granites, granitic gneiss, and acidic intrusives with localized occurrences of sedimentary rock found on the coast. Hummocky and drumlinized, sandy, bouldery, morainal surface deposits dominate the upper surfaces, and deposits occur up to 70 m thick in the eastern part of the ecoregion. Dystric Brunisols are the dominant soils with significant inclusions of Humo-Ferric Podzols and Organic (Mesisol and Fibrisol) soils. Permafrost has little to no ice content, and is limited to isolated patches, mainly wetlands. The highest concentration of wetlands occurs in the area extending 75-150 km inland from James Bay. This ecoregion provides habitat for caribou, moose, black bear, wolf, red and arctic fox, snowshoe hare, grouse, osprey, raven, and waterfowl. Hydroelectric development, hunting, and trapping are the main land use activities. The region contains the largest hydroelectric power development in Canada, the James Bay project. The project contains 5 reservoirs covering 11 900 km2, an area half the size of Lake Ontario. The main communities are Chisasibi and Kuujjuarapik. The population of the ecoregion is approximately 5300.
This ecoregion is part of the Taiga Shield ecozone.