rydberg: vegetative life zones of rocky mountains 481 



the place cited called the Subalpine Zone, for he states: " Hud- 

 sonian, the zone of dwarf spruces, occurs as a narrow belt of the 

 scrubby timber line trees around the high peaks." I am inclined 

 to make the zone broader, including Dr. Merriam's whole spruce 

 zone, or of about the same extent as the Hudsonian Zone of 

 Piper's Flora of Washington.^ I have regarded this zone as 

 extending from the timber line to the average lower limit of the 

 subalpine fir (Abies lasiocarpa) or in Colorado at the upper limit 

 of the bull pine {Pinus scopulorum), i. e., down to about 10,000 

 feet in Colorado, 8,000 in the Yellowstone Park, 6,500 feet in 

 northern Montana, and still lower in the Canadian Rockies and the 

 Selkirks. It would not do to set it at the lower limit of Engelmann 

 spruce or the aspen, for both are found far down into the Montane 

 Zone. A^ Picea Engelmanni is the most characteristic species 

 this zone may be called the Spruce Belt. 



As to the differences between the floras of the Northern and 

 Southern Rockies, they are not very conspicuous in the Subalpine 

 Zone. As stated before, Larix Lyallii is lacking in the Southern 

 Rockies. So are also Tsuga heterophylla and Pmus albicaulis, 

 whose place on the dry ridges is taken by P. aristata. The 

 undergrowth is practically the same, consisting of Arctostaphylos 

 Uva-ursi, Lepargyraea canadensis, Linnaea americana, species of 

 Sambiicus. Pyrola, Aquilegia, Vaccinium, etc. Some of these are 

 also common to the Hudsonian Zone of the East or to the Montane 

 Zone of the Rockies. 



III. Montane Zone 

 This corresponds to the Canadian Zone of Merriam, but it is not 

 like the Canadian Zone of the East. The two important pines 

 of the Canadian forests, Pinus Strobiis and P. resinosa, and the 

 Arbor Vitae, Thuya occidentalis, do not go further west than Lake 

 Winnipeg and only Pinus Banksiana (with the spruces mentioned 

 under the subarctic zone) reaches the foothills of the Rockies. 

 Of the deciduous trees, only Populus tremtdoides, P. balsamifera, 

 Betida papyrifera, and a few willows are comm-on to the East and 

 the Rockies. It is true that some of the undergrowth consists of 

 plants common to both regions, but most of the species of such 

 genera as Vaccinium, Lonicera, Symphoricarpos, etc. are different. 



1 Contr. U. S. Nat. Herb. 11: 1906. 

 32 



