The basic ecological region is the province, a broad vegetation region with considerable climatic unity and one or more related soil groups. Provinces are grouped in divisions defined by climate, soils, and predominant vegetation. Divisions are grouped in domains, defined by climate. Within provinces sections are defined by climax vegetation. This classification follows Crowley's hierarchy of Canadian ecoregions (1967) expanded for the United States by Bailey (1980); for the full reference see the notes. The extended legend (pl 17A) summarizes the principal physiographic areas, soils, flora, and fauna (commonly used by humans) in each province, and the principal landforms and flora in each section.
Although by AD 1500 people had lived in Canada for thousands of years, the prehistoric inhabitants of Canada did not have the technology to modify regional patterns of vegetation, except by fire. The forest border of the Grassland Province appears to have been maintained by fire, but the relative importance of burning caused naturally or by human activity remains uncertain.
Most of Canada could not sustain many people. In most areas the biotic carrying capacity (the extent to which an environment can support animal and plant life) was low and food supplies were dispersed, seasonal, and unpredictable. Game such as caribou, bison, and waterfowl were most available during migrations and fish such as salmon and whitefish during spawning runs. Seal, moose, deer, beaver, and hare were more dispersed but their numbers fluctuated in irregular cycles. In the upper St Lawrence valley and around the lower Great Lakes agriculture made it possible to maintain far higher population densities than in adjacent areas inhabited by hunting and gathering peoples. Along the Pacific coast fish (especially salmon), marine mammals, and shellfish provided dependable foods that supported population densities equivalent to those in agricultural societies.