Boundaries

This ecoregion is defined largely by the St. Lawrence River drainage from the point where the St. Lawrence River leaves Lake Ontario to the Gulf of St. Lawrence. It is bounded by the Ottawa River drainage to the west and Saguenay River drainage to the east. It also covers part of northern New York, northern Vermont, southern Quebec, and southern Ontario.

Topography

This ecoregion forms part of the St. Lawrence geomorphic province (McNab & Avers 1994). The Laurentian Mountains are composed mainly of Precambrian granites and gneisses, and are incised by southward-draining rivers (ESWG 1995). Steep slopes rise abruptly above the St. Lawrence River, and the interior is undulating and covered by glacial drift. To the south lie the Adirondack Mountains in northern New York State. Elevations in the ecoregion extend from sea level to over 1000 m.

Freshwater habitats

Most of the ecoregion’s freshwater habitats were created by glaciation, and include numerous lakes, rivers and wetlands. 

Terrestrial habitats

The ecoregion is comprised of temperate broadleaf and mixed forests, as well as boreal forests. The majority of vegetation is characterized by mixedwood forests dominated by white spruce (Picea glauca), balsam fir (Abies balsamea), quaking aspen (Populus tremuloides), paper birch (Betula papyrifera), and yellow birch (B. allegheniensis). The eastern side of the ecoregion around Lac St. Jean valley is dominated by sugar maple (Acer saccharum), beech (Fagus grandifolia), and yellow birch on upland sites. Eastern hemlock (Tsuga canadensis), balsam fir, eastern white pine (Pinus strobus), and white spruce are the dominant species in valleys (ESWG 1995).

Description of endemic fishes

The copper redhorse (Moxostoma hubbsi) is endemic to this ecoregion. The spring cisco (Coregonus sp.) of uncertain taxonomy is considered endemic to Lac des Écorces, Quebec.

Other noteworthy fishes

In Canada, the chain pickerel (Esox niger), redfin pickerel (Esox americanus americanus), bridle shiner (Notropis bifrenatus), cutlip minnow (Exoglossum maxillingua) and eastern silvery minnow (Hybognathus regius) are largely limited to this ecoregion, and all likely originated from an Atlantic refugium.

Ecological phenomena

This ecoregion was noted for runs of catadromous American eel and anadromous Atlantic salmon; however, stocks of both these species are declining.

Justification for delineation

The ecoregions of Canada were identified based on the faunal similarity of 166 major watersheds based on a cluster analysis of freshwater fish occurrences in these watersheds. The St. Lawrence Ecoregion contains watersheds that drain into the St. Lawrence River, a dispersal corridor for freshwater fishes. Given its close proximity to glacial refugia and moderate climate, the fish fauna of this ecoregion is relatively diverse and most characteristic of the fauna derived from the closest refugium – the Atlantic refugium.

Level of taxonomic exploration

Good