tertiary forest doubtless had a fairly uniform fauna 

 from eastern Canada across the Bering land bridge to 

 western Europe. This fauna became differentiated 

 into the three biociations with the disappearance of 

 the Bering land connection between Alaska and Asia, 

 and the separation of the North American fauna into 

 western and eastern sections by the northward pene- 

 tration of grassland and the southward movements 

 of the Pleistocene glaciers. Differentiation at the sub- 

 species and species levels was further encouraged by 

 the segregation of the North American fauna during 

 Pleistocene glaciation in the Appalachian, Rocky 

 Mountain, Pacific, and Alaskan refvigia. 



Animal adaptations are similar to those in the 

 deciduous forest, but often more extreme. Boreal 

 species, for instance, must have greater physiological 

 tolerance to cold to remain active over winter. Mi- 

 gration is also more extensive, although in mountain- 

 ous areas migration is largely altitudinal rather than 

 longitudinal. Browsing is more common, for the 

 ground during winter months is generally covered 

 with snow. Insects often cause considerable damage 



to forest trees, and mosquitoes and flies are annoying 

 both to animals and man. 



White man is relatively less numerous in this 

 biome in North America than are Indians. Chief oc- 

 cupations are logging, hunting and trapping, and 

 mining. 



Woodland and chaparral biociations have some 

 distinctive animal species but in many areas tend to 

 be ecotonal between coniferous forest and grassland 

 or desert. 



The zonation of communities on mountains de- 

 pends principally on decrease in temperature with 

 increase in elevation. In western North America, 

 desert or grassland, woodland or chaparral, conifer- 

 ous forest, and alpine tundra occur at successively 

 higher elevations. 



In the Western mountains the following exam- 

 ples of zonation of communities are of interest, the 

 elevations given being the mean lower limits of the 

 communities. It is evident that identical communities 

 occur at lower elevations in the North than in the 

 South. 



Locality 

 Authority 

 Desert or grassland 

 Pinon-juniper woodland 

 Petran montane forest 

 Coast forest ecotone 

 Petran subalpine forest 

 Alpine tundra 



Northern Arizona 



Merriam 1890 



below 1830 m (6000 ft) 

 1830 m (6000 ft) 

 2135 m (7000 ft) 



absent 

 2800 m (9200 ft) 

 3500 m (11,500 ft) 



Idaho 



Larsen 1930 

 300 m (1000 ft) 



absent 

 300 m (1000 ft) 

 615 m (2000 ft) 

 1700 m (5500 ft) 

 2300 m (7500 ft) 



Locality 



Authority 



Coast forest 



Grassland 



Oak-woodland and coastal chaparral 



Sierran montane forest 



Sierran subalpine forest 



Alpine tundra 



California 



Hughes & Dunning 1949 



absent 



below 150 m (500 ft) 



150 m (500 ft) 



760 m (2500 ft) 



1980 m (6500 ft) 



3350 m (11,000 ft) 



Washington 



Taylor 1922 

 sea level 



absent 



absent 



absent 

 1385 m (4500 ft) 

 2000 m (6500 ft) 



314 Geographic distribution of communities 



