8 
INTRODUCTION 
central provinces it is practically co-extensive with the prairies, ceasing 
against the spruce forest of the north and the slopes of the mountains to 
the west. In British Columbia it follows up the warm interior valleys to 
the vicinity of the Canadian Pacific Railway and along the coast in a 
narrow belt to a point opposite the head of Vancouver Island, including 
also most of the east coast of that island. 
The Boreal region is divided into Canadian, Hudsonian, and Arctic 
zones. The Canadian zone includes the coniferous forested region north 
of the Transition to the limit of practical cultivation. It sends intrusive 
fingers far north along Mackenzie Valley and Peace River and up the west 
coast, including most of the immediate coast and islands of the Alaska 
Panhandle almost to Skagway. The Hudsonian zone is the more northern 
country of small shrubs and stunted tree growth and is generally unsuit- 
able for agriculture. The Arctic zone includes the Barren Grounds north 
to the pole. 
These life zones are based fundamentally on temperature and if 
physiographic conditions were uniform would be determined by latitude. 
However, they are deflected from their natural east and west sweep by 
the shielding effects of mountain ranges, the vicinity of large bodies of 
water and warm or cold ocean currents, temperature of prevailing wind, 
and elevation. Hence the very irregular boundaries of these zones across 
our continent. 
Elevation is an important factor in the distribution of life. Even in 
the tropics, the top of a mountain high enough will be of extreme arctic 
character with perpetual snow, and down its sides at their proper elevation 
will be found belts of the above zones. This is well exemplified in the 
mountainous region of British Columbia, The mountain tops may be of 
Hudsonian character, their peaks even Arctic, and the valleys between 
may descend to Canadian, Transition, or even Upper Austral. Conse- 
quently, the zones that on the level prairies are separated by hundreds 
of miles may, in this more rugged country, be within a few hours climb of 
each other. Also, elevations here and there in level country may produce 
islands of more northern life associations in southern zones. Thus, along 
the southern boundary in the Prairie Provinces, we find Turtle Mountain 
and Cypress Hills as Boreal islands surrounded by Austral lowlands; and 
a long, narrow tongue of Hudsonian zone follows the backbone of the Rocky 
Mountains from northern British Columbia south across the boundary line. 
Ocean currents have an important effect on the climatic conditions of 
the shores adjoining them. The fact that Land’s End in England, washed 
by the last energies of the warm Gulf stream, is in the same latitude as 
bleak Labrador, bathed by a cold Arctic current, well illustrates this. 
On the Pacific, the great Japan current sweeps against our coast and pro- 
longs Canadian zone conditions as far north as the latitude of southern 
Greenland, and moderates the climate of southern Alaska and the far- 
flung Aleutian islands to a surprising mildness. 
Besides these purely thermal controls of climate, there are other 
influences. Important among these is rainfall. The west coast, bathed in 
winds moisture-laden from the warm sea, receives a copious rainfall and 
the vegetation is almost tropical in its profusion. These rain-laden winds, 
robbed of most of their moisture by the cold peaks of the coastal range, 
pass on over to the interior valleys of British Columbia and the prairie 
regions beyond, which are consequently dry, and in some cases almost arid. 
