20 MISC. PUBLICATION 42 3, U. S. DEPT. OF AGRICULTURE 



elevation pinyon is the dominant or, in some places, the only tree. 

 A narrow belt of xeric evergreen forest surrounds the Mogollon Mesa, 

 stretches over wide areas in Coconino County, and covers the plateaus 

 and mesas of Navajo and Apache Counties at elevations between 

 6,000 and 7,200 feet. The alligator juniper, common in the moun- 

 tains of the southern part of the State, is less frequent in central 

 Arizona and absent from the northern part. The oneseed juniper 

 is the common form along both edges of the Mogollon Mesa. Junip- 

 erus utahensis (Utah juniper) is the commonest form in the extreme 

 north. In Yavapai County and some of the adjacent regions all of 

 these junipers^may be found, together with J. scopulorum (Rocky 

 Mountain juniper). Pinus cembroides, the common pinyon of the 

 southernmost counties, is absent from the northern half of the State 

 where the commonest form is P. edulis (pi. 6) . 



There are no other trees that deserve mention as common, or even 

 infrequent, components of this type of forest. Along the streams 

 and drainageways are found several deciduous trees, notably Fraxinus 

 velutina (ash), Quercus gambelii (Gambel oak), Platanus wrightii 

 (sycamore), Populus jremontii (cottonwood) , Acer grandidentatum 

 var. brachypterum (maple), and Acer negundo var. interius (boxelder). 



Northern Mesic Evergreen Forest.— The mesic forests of 

 Arizona are predominantly made up of needle-leaved evergreen 

 trees, and in their physiognomy and ecological characteristics are very 

 similar to the coniferous forests that cover the higher elevations of 

 the Rocky Mountain region. This is predominantly a pine forest, 

 and, as represented in Arizona, presents some marked differences in its 

 floristic composition from the forests of the States to the north and 

 northeast. The mesic forest is confined to the mountains and higher 

 elevations of the State and is commonly surrounded by xeric evergreen 

 forest. The larger bodies of mesic forest extend from northwestern 

 to eastern central Arizona, over the region of highest altitude, and 

 smaller bodies of it occur in the extreme northeast, in the central 

 counties, and in the southeast. Some of the smallest bodies are 

 found in small mountain ranges, where they are very effectively 

 isolated from the larger areas (pi. 7). 



From both the physiognomic and floristic standpoints the mesic 

 forest is naturally divisible into drier and more open pine forests and 

 moister closed spruce and fir forests. The lower limit of pine forest 

 varies from 6,000 to over 7,000 feet, according to local conditions, 

 and its upper limit is about 9,000 feet. The spruce and fir forest 

 ranges from about 7,000 or 7,500 feet to about 11,000 feet, at which 

 elevation it is open and stunted. 



The pine forests are dominated north of the Gila River by Pinus 

 ponderosa (western yellow pine) and in the south by Pinus arizonica 

 (Arizona pine). With respect to the plants associated with these 

 trees there are some striking differences between the forest of the 

 desert mountains south of the Salt River and those of the Mogollon 

 Mesa. In the former are to be found many plants that have their 

 principal areas in Mexico and reach their northern limits in southern 

 Arizona. In the desert mountains the lower limit of the pines is 

 formed by Pinus latifolia (Apache pine) or by P. leiophylla (Chihua- 

 hua pine) and the upper limit by P. strobiformis (Mexican white. pine), 

 all of which are confined to the southern half of the State. A consider- 

 able number of shrubs and root perennials that are found in the pine 



