This ecoregion stretches from the Gaspé Peninsula at the mouth of the St. Lawrence River southwesterly through the Appalachian complex of eastern Quebec to the United States border, south of Sherbrooke. The climate is characterized by warm summers and snowy, cold winters. The mean annual temperature of the ecoregion is approximately 3.5°C. The mean summer temperature is 14.5°C and the mean winter temperature is -8°C. The mean annual precipitation ranges 900-1300 mm. In the higher elevations of the Notre Dame Mountains of the central Gaspé Peninsula annual precipitation can exceed 1300 mm and annual temperatures are colder. The mean annual temperature at Murdochville is 1.5°C. Vegetation on the mountains is characterized by closed coniferous forests that are dominated by black spruce and balsam fir with a moss ground cover. Paper birch is common. Mixedwood forests dominate southwest of Matane, including sugar maple, beech, and yellow birch on upland sites, while eastern hemlock, eastern white pine, balsam fir, and white spruce prevail in the valleys. On moist sites red maple, black ash, white spruce and tamarack are dominant. The Notre Dame Mountains are the central part of the old Appalachian peneplain, where the elevation varies 400-1200 m asl. The Chaleur Uplands, also part of the old Appalachian peneplain, range 450-600 m asl on the lower slopes. Composed of folded Devonian shale, limestone and sandstone, their slopes are steep, and surficial deposits, mainly morainal in origin, are thin and discontinuous. Scree slopes, colluvium, and peatlands in depressions are also present. The Appalachian complex along the south shore of the St. Lawrence River is dominated by folded Palaeozoic sandstones and quartzites. Relief varies from hummocky to mountainous. The average elevation is 400 m asl, but peaks above 600 m asl are common. Fluvioglacial deposits occur only in the valleys. Differential erosion of the hard and soft rocks have resulted in the development of broad sloping uplands and lowlands in the Appalachian peneplain south of Rivière-du-Loup. The Sutton Mountains, a continuation of the Green Mountains of Vermont and the Megantic Hills, a part of the White Mountains of New England, reach above 950 m asl in places. Although the soils are often shallow, the soft, vertically fractured rock permits deep rooting. Moderately fertile Podzols are the dominant soils in the ecoregion. The other significant soils are Dystric Brunisols and Gleysols. Characteristic wildlife includes moose, black bear, white-tailed deer, beaver, porcupine, bobcat, red fox, lynx, marten and rabbit. Seabirds and shorebirds are common on the Gulf of St. Lawrence coast. The region's major land uses are agriculture, forestry and recreation, and tourism. Farmland occupies approximately 15% of the ecoregion, primarily along the St. Lawrence River plain and the valleys and lowlands below 300 m asl. The major communities include Sherbrooke, Thetford Mines, Rimouski, Matane, Murdochville, and Gaspé. The total population of the ecoregion is approximately 707 300.
This ecoregion is part of the Atlantic Maritime ecozone.