44 THE UNIVERSITY OF OKLAHOMA 



frc'm th: Divide in Colorado to the eastern border of this State. 

 In doing this we will include all the zones except the Tropical. 



The Artie-Alpine zone is the entire area above the isotherm 

 10°C. (50°F.) for the hottest consecutive six weeks. This iso- 

 therm corresponds remarkably well with the timber line. The 

 best plant indicators are an alpine willow (Salix pctrophila), a, 

 stemless catchfly (Silene acaulis) and a rather conspicuous com- 

 posite herb, Rybcrgia graudifolia. Among the animal indicators 

 we find the white-tailed ptarmigan (A. O. U. No. 304), the brown- 

 capped rosy firich (No. 526) and the pipit (No. 697). The rock 

 cony, or pika (Ochotoua saxatilis Bangs) breeds commonly but 

 not exclusively in this zone. 



Beginning at timberkne the Hudsonia zones extend to the 

 isotherm 14°C. (57.2° F.) for the six weeks. Engelman spruce 

 (Picca dhgielmaiuni) and balsam fir (Abies lasiocarpa) are the' 

 most conspicuous plant indicators while the Rocky Mountain pine 

 grosbeak (No. 515a) and Clarke Nutcracker (No. 491) are 

 animals restricted to this zone during breeding. 



The lodgepole pine belt lies within the Canadian zone, the 

 lower limit of which is the isotherm 18°C. (64.4°F). In addition 

 to the lodgepole pine (Finns Miirrayana) the aspen (Populus 

 termuloides) the Rocky Mountain jay (No. 484) and the Alpine 

 three-toed woodpecker (No. 401B) and the broad-tailed beaver 

 (Castor canadensis trondator) are good indicators. 



The Transitional zone, or foothill belt, includes the rock pine 

 (Finns ponder osa) and the Douglas fir (Pseudotsuga taxifolia) 

 forests, and its southern limit is the isotherm 22° C. (71.6°F). 

 This zone almost reaches the panhandle of Oklahoma on the west. 



The Upper Austral, or Upper Sonoran, includes the grassy- 

 plains of the middle west and much of the timber land farther 

 east down to isotherm 26°C. (78.8°F). This is the great wheat 

 belt where there is a sufficient amount of moisture. 



The panhandle of Oklahoma and a narrow strip of Harper 

 and Ellis counties are considered by Merriam to be within the 

 Upper Sonoran. The pinyon pine (Finns edulia), the tree cactus 

 (Opuntia arboresccns), the chesnut-faced pocket gopher (Crato- 

 geomys castanopsj, the black-tail jack rabbit (Lepus calif ornicus 

 melanotis,) the burrowing owl (No. 378) and the Bullock oriole 

 (508) are the most conspicuous indicators. 



The rest of the Upper Austral includes those areas in the 

 Ozarks, Ouachita, and Wichita mountains which lies above isotherm 

 zee. The short leaf pine (Finns echinata) makes its appearance 



