RYDBERG: VEGETATIVE LIFE ZONES OF ROCKY MOUNTAINS 483 



Mountains are found on the western slope of the Northern Rockies. 

 Some have also migrated across the Great Basin from the Sierra 

 Nevada to the Southern Rockies, or vice versa from mountain to 

 mountain. Of the forest trees may be mentioned the following 

 categories: (i) Species of general distribution in both regions: 

 Pinus Murrayana, P. flexilis, P. albicaulis, Psendotsuga miicronata, 

 Alniis tenuifolia, Popiilus tremuloides, and Pinus ponderosa, if 

 Pinus scopulorum is included in it as a variety. (2) Species com- 

 mon to the Sierra Nevada and the Southern Rockies: Abies con- 

 color and Pinus aristata. (3) Western species, whose ranges 

 extend to the western slopes of the Rockies: Larix occidentalis, 

 Abies grandis, Tsuga heterophylla, Thuya plicata, Pinus monticola, 

 Taxus brevifolia, Populus trichocarpa, Betula occidentalis, etc. 

 These may all be regarded as immigrants. (4) Rocky Mountain 

 species which have migrated into the Cascade Mountains but 

 which are not found in the Sierra Nevada, as Picea Engelmanni 

 and Abies lasiocarpa. (5) The endemic species confined to the 

 Rockies only are: Picea Parryana, P. albertiana, Populus angusti- 

 folia, Betula fontinalis, etc. From this it may be inferred that 

 the difference between the Montane Zone in the Rockies and the 

 Pacific Mountains is much less than between the former and the 

 Canadian Forest. The mountains of the Pacific slope and the 

 Rockies might be included in the same province, were it not for the 

 lack in the latter of many of the most characteristic trees of the 

 former, as for instance, the sugar and other Californian pines, 

 the redwoods and "big trees," the cypresses, etc. 



Many differences are found between the Montane Zone of the 

 Northern and of the Southern Rockies. Here it may suffice to 

 give a summary of the differences in the composition of the forest 

 trees from an article already published, (i) Trees common to 

 the both divisions are Pinus Murrayana, P. scopulorum, P. flexilis, 

 Pseudotsuga mucronata, Picea Engelmanni, Sabina scopulorum, 

 Populus tremuloides, P. balsamifera, and P. angustifolia, Betula 

 fontinalis, Alnus tenuifolia, and several willows. (2) Trees found 

 in the Southern but not in the Northern Rockies are: Picea Parry- 

 ana, Abies concolor, and Betula utahensis. (3) Those found in 

 the Northern Rockies but not in the Southern: Picea albertiana, 

 Pinus albicaulis, several species of Betula, Populus, and Salix, 

 and the conifers mentioned above as immigrants from the Cascade 

 Mountains. 



