PHYSIOGEAPHY AND LIFE ZONES. 19 



temperature or climate, while large numbers of species have approxi- 

 mately the same climatic and consequently geographic range. Ac- 

 cording to well-known laws the climate normally becomes colder as 

 the altitude and latitude become higher, but not uniformly, as slopes 

 inclined toward the south receive and absorb more heat from the 

 sun's rays than do level areas, and far more than the slopes inclined 

 toward the north. Thus slope exposure greatly modifies the local 

 climatic conditions and consequently the distribution of plant and 

 animal life. The altitude of the base level, or country surrounding 

 the base of the mountains, also in part determines the amount of heat 

 available to the slopes above. A high base level holds the sun-warmed 

 air up against the sides of the mountains and thus enables associated 

 sjiecies to grow at higher levels than where the surrounding country 

 is lower. Many other local influences, as air currents, prevailing 

 winds, light and shade, humidity, and soil conditions, further modify 

 the environment that determines the nature of the fauna and flora. 



The open plains country, which barely penetrates the eastern edge 

 of the park, supports the peculiar types of plant and animal life be- 

 longing to the Transition Zone, traces of which are found also in the 

 lower valleys on the west slope of the park. The dense forests of 

 lodgepole pine, spruce, and fir, which cover the base of the moun- 

 tains, mark the Canadian Zone; the narrow belt of dwarfed timber 

 at and near timberline, the Hudsonian Zone; while depauperate 

 plants above timberline partly cover the peaks and ridges of the 

 Arctic- Alpine Zone. 



TRANSITION ZONE. 



The Transition Zone, an area relatively warm and fertile and of 

 value for the production of wheat and other cereals, lies mainly out- 

 side the park, but fortunately enough of it is included to add souie 

 of its characteristic species to the fauna and flora of the park and 

 lo provide suitable winter range for some of the important game 

 jinimals of the higher and colder zones. On the east slope it is 

 present in dilute form up to about 4.500 feet altitude on the warmest 

 exposures, those facing toward the southwest at (Jlacier Station, aud 

 in the St. Mary, Swiftcurrent, and Belly River Valleys. It is indi- 

 cated by tongues or patches of prairie carrying the prairie species 

 of plants and animals, and is mainly without timber. Its shrubby 

 vegetation consists of the little western birch, the diamond willow, 

 serviceberry, silver-leaf, western snowberry, prairie rose, and creep- 

 ing juniper, but its dominant vegetation consists of prairie grasses 

 mixed with the loco, vetch, milk vetch, bluebonnet, brown-eyed Susan, 

 balsam root, prairie aster, blazing star, Indian paintbrush, larkspur, 

 puccoon, geranium, purple wind flower, and a host of other plants 

 of the Great Plains Transition Zone area. Its characteristic mam- 



