Hudson Bay lowlands

• Category: Forest Biomes.
• Geographic Location: Canada.
• Summary: The Hudson Bay Lowlands biome is the largest wetland in North America, but the region faces significant changes as a result of isostatic rebound and climate change.

The Hudson Bay lowlands are the largest wetland area in North America, covering a vast expanse of Canada between the Canadian Shield and the southern shores of Hudson and James Bays. Encompassing parts of the Canadian provinces of Manitoba, Ontario, and Quebec, the lowlands are along the ecotone (overlap) between the boreal forest to the south and the Arctic tundra to the north. The area faces significant change, however, from the effects of climate change as well as the isostatic rebound (rising ground elevation) of a landscape once burdened by the fantastic weight of continental ice-age glaciers. The region is still rebounding from the Laurentide Ice Sheet at some of the fastest uplift rates in North America (on the order of ~0.7–1.2 cm per year in parts of the Hudson Bay–James Bay lowlands), reshaping shorelines and drainage as land rises relative to sea level.

The location of Hudson Bay and the lowlands to its southwest and south correspond with the approximate center of the Laurentide Ice Sheet—the massive ice load that covered North America during the Pleistocene period, before it retreated and melted some 20,000 years ago. The massive weight of that ice, which was as much as two miles thick, compressed the ground below, allowing incursion of salt water in areas far beyond the shores of Hudson Bay. In addition, the ice scoured the ground beneath it, effectively bulldozing or filling in the original drainage network and ensuring, because of that disrupted drainage, that large swaths of the region would remain wet and bogged down after the glaciers retreated.

The landforms left behind include gravel ridges and hills—usually derived from glacial deposits—raised beaches, occasional rocky outcrops, permafrost hummocks, and extensive lowlands filled with glacial or marine sediments. Upland areas are often dominated by boreal forest vegetation, in particular white spruce—one of the dominant species of the North American boreal forest—with balsam fir, quaking aspen, balsam poplar, and paper birch. Important plant associates include dogwood, willow, lingonberry, bearberry, twinflower, miterwort, false toadflax, wintergreen, or mosses such as Hylocomium or Pleurozium. Stands of black spruce and jack pine may also be important components of the forests of upland sites.

Lowland and Wetland Types

The type of lowland sites are influenced in large part by site conditions. Tundra, dominated by shrubs such as blueberry, lingonberry, bearberry, and lichens such as Cladonia, occurs in relatively well-drained sites in a strip along the Hudson and James Bay coasts. On poorly drained sites, bogs develop under acidic conditions, and fens develop under neutral or alkaline conditions. Both develop in poorly drained areas, where organic matter may accumulate over time. The Hudson Bay Lowlands biome features an abundance of both.

Beyond biodiversity, the Lowlands are globally important because their deep peat stores enormous amounts of soil carbon, spatial estimates placing the total peat carbon storage around ~30 ± 6 Petagram, meaning that hydrological change, thaw, and fire can have climate-relevant consequences. Field measurements in a Hudson Bay Lowlands subarctic peatland show that active-layer thaw depth increased significantly between 2012 and 2024, with landform type (fen vs. palsa/peat plateau) influencing the rate of thaw.

A common type of wetland in the Hudson Bay Lowlands is the muskeg. The nutrient-deficient substrate often supports an open stand of black spruce, but the muskegs are dominated by mosses such as Sphagnum, with a handful of shrubs such as Labrador tea, dwarf willow, and dwarf birch. Another type of muskeg is dominated by Cladonia lichens, with shrubs such as Labrador tea and blueberry.

While raised bogs appear to be higher in elevation than the surrounding tundra, their elevation results from the accumulation of peat in areas that were once lower in elevation than the surrounding landscape. The sites are poorly drained, much like a raised wetland, and as such are dominated by black spruce, a common resident of wetland areas throughout the North American boreal forest. Another type of raised bog, the palsa, features a permafrost core, with the raised elevation the result of action by the ice. Black spruce is again the more noticeable dominant, but palsas have significant cover by Labrador tea, blueberries, and sedges.

Fens are often dominated by tamarack, with dwarf birch and bog willow; mosses such as Tomentypnum, Drepanocladus, and Campylium; sedges; and cottongrass.

In tidal flats and estuaries along the shores of Hudson and James Bays, a type of sedge-dominated marsh may develop. In addition to sedges, grasses such as tundra grass, alkali grass, pendant grass, and arrowgrass, and herbs such as primrose, bog star, and felwort are common.

Other vegetation types in the region include the dwarf birch-willow communities that flank marsh flats and river shorelines, and balsam-poplar communities found on alluvial and beach deposits.

Fauna and Change

Several large rivers flow through the Hudson Bay Lowlands into the Hudson or James Bays. Rivers that flow into Hudson Bay include the Churchill, Nelson, Hayes, Severn, and Winisk Rivers. Those that flow into James Bay include Attawapiskat, Albany, Moose, Harricana, and Nottaway Rivers. Whales such as beluga may be spotted in the larger river estuaries, such as that of the Churchill River near Churchill, Manitoba.

The Hudson Bay Lowlands biome is undergoing great change. One cause is geological: The Hudson Bay region is undergoing isostatic rebound, in which the landscape, formerly compressed under the great weight of the Laurentide Ice Sheet, is expanding vertically, in effect, getting higher. Vegetation belts shift northward to colonize land exposed by the retreating waters.

The other cause is climatic. Climate change is causing the landscape to warm. Some of the more striking effects are over the Hudson and James Bays, where the icepack melts earlier and freezes later. But warmer temperatures disrupt the landscape as well, melting permafrost, increasing loss of water from the land surface via evaporation and transpiration, and increasing the risk of wildfire in the region. While wetlands may be the most heavily affected by the change, upland ecosystems are likely also to be adversely affected.

Researchers have aimed to study how these changes in climate may affect the flora and fauna of the biome. A study explained how one of the few amphibians of the area, the wood frog, may be affected by temperature changes. Tadpoles of this species require up to two months to develop into frogs before the onset of summer. Climate change in the region is shortening the window of time between snowmelt and summer, which in turn may cause the frogs to be smaller. Further, changes in rain patterns may alter the water levels in ponds of the region, impacting tadpoles and adult frogs. This is just one of many species that may be altered by the changing climate.

Hudson Bay marine conditions are changing rapidly: in spring 2024, southeastern Hudson Bay experienced record early sea-ice loss and an unusually long ice-free season, changes likely to affect coastal climate and nearshore ecosystems that influence the Lowlands.

Bibliography

Abell, Robin, et al. “Freshwater Ecoregions of the World: A New Map of Biogeographic Units for Freshwater Biodiversity Conservation.” BioScience, vol. 58, no. 5, 2008, pp. 403–14, doi:10.1641/B580507. Accessed 2 Feb. 2026.

Abraham, K. F., and C. J. Keddy. “The Hudson Bay Lowland.” The World’s Largest Wetlands: Ecology and Conservation, edited by L. B. Fraser and P. A. Keddy, Cambridge University Press, 2005, pp. 118–48, doi:10.1017/CBO9780511542091.005. Accessed 2 Feb. 2026.

Barbour, Michael G., and William Dwight Billings. North American Terrestrial Vegetation. 2nd ed., Cambridge University Press, 1999.

Larsen, James A. The Boreal Ecosystem. Academic Press, 1980.

Li, Yiyao, et al. “Peat Depth and Carbon Storage of the Hudson Bay Lowlands, Canada.” Geophysical Research Letters, 30 Dec. 2024, doi:10.1029/2024GL110679. Accessed 2 Feb. 2026.

Morison, Matt, and Nora Casson. “How Climate Change Is Impacting the Hudson Bay Lowlands—Canada’s Largest Wetland.” The Conversation, 14 May 2023, theconversation.com/how-climate-change-is-impacting-the-hudson-bay-lowlands-canadas-largest-wetland-203821. Accessed 2 Feb. 2026.

Muir, Gillian, et al. “Active Layer Thermal Regime Varies Across Landforms in a Subarctic Wetland.” Facets, 2025, doi:10.1139/facets-2024-0250. Accessed 2 Feb. 2026.

“Ontario: The Geology of Rising Land – Isostatic Rebound.” Ontario Beneath Our Feet, 17 Nov. 2020, www.ontariobeneathourfeet.com/rising-land-isostatic-rebound. Accessed 2 Feb. 2026.

Ritchie, J. C. “The Vegetation of Northern Manitoba: II. A Prisere on the Hudson Bay Lowlands.” Ecology, vol. 38, no. 3, 1957, pp. 429–35.

Sjörs, Hugo. “Bogs and Fens in the Hudson Bay Lowlands.” Arctic, vol. 12, no. 1, 1959, pp. 2–19.

Soriot, C., et al. “Record Early Sea Ice Loss in Southeastern Hudson Bay in Spring 2024.” Geophysical Research Letters, 15 Jan. 2025, doi:10.1029/2024GL112584. Accessed 2 Feb. 2026.