Because plant growth is so definitely under the influence of moisture supply and temperature, geographers have long recognized the importance of the pattern of natural vegetation. In fact the climatic types of some regions are more often known by the names of their associated types of vegetation as, for example, tundra, selva and savanna. In spite of this no full study of the plant geography of Canada has yet been undertaken. Adams' "Flora of Canada" gives useful information on a very broad regional basis. Halliday "Forest Classification For Canada" is also most useful but it deals only with forest trees which, while the most noticeable, are not necessarily the most important elements of the plant cover. The exact relationships of forest distribution to various climatic factors are not yet completely understood and no maps have yet been drawn which show the exact climatic controls of the various forest types in Canada. Certain broad correlations, however, do appear.The simplest concept is probably that of the climax association. Theoretically a particular climate favours the selection of certain species which tend to become a balanced and stable plant community. Thus a maple-beech-basswood hardwood forest characterizes a large part of southern Ontario while western hemlock and western red cedar dominate the forest of the Pacific coast. The vegetation region, however, is much more complex for it must take into consideration, also, all the various sub-climax association. The denudation of a forest area by fire is followed by an entirely different plant association. In certain parts of Nova Scotia, for instance, the burning of a mixed spruce, balsam fir, red maple stand is followed by blueberries, wire birch and tamarack. In the Lake Superior region, mixed forests are followed by aspen and white birch in many cases.Edaphic conditions also cause great variation in the forest cover. In eastern Ontario, the rolling hill lands of Glengarry carry an association of sugar maple, beech and white cedar, the adjoining clay plains are characterized by elm, ash and soft maple. Sand plains in the same locality originally had magnificent stands of white pine. All these variations must, of course, be comprehended within the same vegetation region.Vegetation regions must take into account not only the plants which can be identified, but also the plant communities or associations, the density of the stand and type of growth, and the apparent adaptation of the various species to the environment. White spruce, for instance, is found from Nova Scotia to the Yukon and is characteristic of the great Boreal Forest which, in most geographies, stretches unbroken over most of the land mass of Canada. Balsam fir, tamarack, aspen and white birch are almost as widespread. The growth and appearance of these trees in the northern "land of little sticks", however, is very different from that in the southern part of the country.Having in mind the foregoing points, the accompanying map of vegetation regions was drawn up. Its main boundaries are fairly close to those of Halliday, but it has not been possible to show all the small areas of different vegetation types which exist in the Cordilleran region. Fourteen vegetation regions, accordingly, will be discussed in the following paragraphs.
1. Arctic Tundra.
2. Subarctic or Transition Forest Region.
3. Boreal Forest Region or Taiga.
4. Pacific Coast Forest Region.
5. Rocky Mountain Forest Region.
6. Alpine Tundra.
7. Columbia Forest Region.
8. Montane Forest Region.
9. Central Mixed Woods Region.
10. Aspen Grove or Parkland Region.
11. Prairie Region.
12. Great Lakes--St. Lawrence Forest Region.
13. Niagara Forest Region.
14. The Acadian Forest Region.