THE FLORA OF THE WILLIAMS DIVISION OF THE 

 TUSAYAN NATIONAL FOREST, ARIZONA 



A. D. READ 



Forest Service, Albuquerque, New Mexico 



The Tusayan National Forest lies on the extreme edge of the 

 Colorado Plateau in northern Arizona, west of Flagstaff and 

 south of the Grand Canon. The lowest portion of the Forest 

 is about 5000 feet in elevation, lying just below the edge of the 

 Plateau, and the highest portions are the summits of Bill Wil- 

 liams, Sitgreaves and Kendrick Peaks, which rise to the vicinity 

 of 10,000 feet. The major portion of the Forest is comprised 

 in the rolling surface of the Plateau, lying between 6500 and 

 8000 feet. By reason of its diversity of topography and range 

 of elevations the Tusayan Forest comprises four life zones, the 

 Upper Sonoran, Transition, Canadian, and Hudsonian. 



UPPER SONORAN 



This zone occurs at elevations of 5000 to 7000 feet and con- 

 tains three main types; woodland, the tree species of which 

 consist almost entirely of pinon (Pinus edulis) and juniper 

 (Juniperus monosperma) , brush areas covered chiefly with shin 

 oak (Quercus grisea), and parks or treeless areas supporting 

 grasses and weeds. 



Probably 50% of the herbaceous vegetation in this zone is 

 blue grama (Bouteloua oligostachya) . Some sideoats grama (B. 

 curtipendula) grows on the rocky south slopes. A three-awn 

 grass, Aristida arizonica, is quite noticeable because of its long 

 reddish purple awns or beards. Snakeweed {Gutierrezia spp.), 

 rabbit bush (CJtrysothamnus spp.) and pingue (Hymenoxys 

 floribunda) are abundant, growing usually in pure stands in the 

 open where the}' cover many acres to the exclusion of other 

 species. Snakeweed and rabbit bush are worthless, being un- 



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