rydberg: vegetative life zones of rocky mountains 479 



Canadian, Transition, and Upper Sonoran. I have preferred the 

 names given above rather than those of Merriam, because the 

 former have been used by many authors in Europe in articles on 

 the phytogeography of the Alps and other mountain regions. 

 Furthermore, I do not like the names Hudsonian and Canadian 

 as applied to the Rocky Mountains, for the Rockies have none 

 of the characteristic forest trees in common with the Hudson Bay 

 Region or Canada proper. The only ecologically important tree 

 common to both regions would be the quaking aspen, which is 

 not a tree characteristic of either zone, and some botanists regard 

 the western aspen as distinct from the eastern. When the life 

 zones are so unlike as they are in the East and in the Rockies, 

 I think that they should have different names. It would be as 

 misleading to call our Austro-riparian zone of the Southern 

 States the Lower Sonoran zone, which is the name of the corre- 

 sponding zone of the West. 



The Rockies are surrounded by plains or tablelands, either 

 grasslands or desert regions, some belonging to the Submontane 

 and others to the Upper Sonoran. 



Besides these zones long tongues of others intrude into the 

 Rocky Mountain region, viz. several of the Prairie regions, especi- 

 ally along the Arkansas, Platte, and Missouri rivers and one from 

 the Lower Sonoran along the Colorado of the West. The true 

 Hudsonian and Canadian zones also touch the Rockies at the 

 headwaters of Athabasca River and northward. 



L Arctic- Alpine Zone 

 This is represented in the Rockies by numerous islands along 

 the mountain chain and shows very little variation in composition 

 throughout the whole range. It is true that the Northern Rockies 

 contain more of the circumpolar arctic plants, and the percentage 

 of endemic species is somewhat larger in the Southern Rockies, 

 but the general make-up is practically the same. The arctic- 

 alpine zone comprises the tops of the higher mountains above the 

 timber line. The altitude of the latter varies a good deal even 

 in the same locality, but is found in Colorado between ii,ooo 

 and 12,000 feet, in Montana between 7,500 and 9,000 feet altitude, 

 and in the Canadian Rockies still lower. In the north the timber- 

 line comes down practically to the sea-level near the arctic coast 



