Pinyon-Juniper in the Southwest 



343 



second one, the evergreen-oak type, is 

 found mostly in Arizona at elevations 

 of 4,500 to 6,000 feet, and is made up 

 largely of Arizona and Emory oak; it 

 is of considerable importance in its 

 area. The third type is the pinyon- 

 juniper, with which we are here con- 

 cerned. 



The pinyon-juniper type occupies 

 an area in Arizona and New Mexico 

 far in excess of all other forest types 

 combined. The area is estimated at 17 

 percent of the total area of both States, 

 or some 25 million acres. This forest 

 is fairly well distributed over the two 

 States, except in the eastern part of 

 New Mexico and western and southern 

 Arizona. The pinyon-juniper forest 

 occurs below the ponderosa pine at 

 elevations of about 5,000 to 7,000 feet. 

 The lower elevation at which the for- 

 est occurs is determined by lack of 

 moisture. Annual precipitation in the 

 Southwest increases with increased ele- 

 vation. The annual precipitation in the 

 pinyon-juniper areas is from 12 inches 

 at the lower edge to 18 inches at the 

 upper limits. Some 50 to 60 percent 

 of the moisture falls between May and 

 September. 



The moisture requirements place the 

 pinyon-juniper type in a belt of vary- 

 ing widths around the mountains and 

 on the mesas that are higher than 5,000 

 feet. The presence of forest and its type 

 and density give the traveler in the 

 Southwest a measure of the total pre- 

 cipitation at a given point. The open 

 stands of pinyon-juniper indicate pre- 

 cipitation of 12 to 14 inches. The 

 denser stands indicate 16 to 18 inches 

 of rain and snow. The saw-timber for- 

 ests of ponderosa pine and the others 

 indicate a total of 19 to 25 inches. 



Soils of all classes appear to be ac- 

 ceptable to pinyon and juniper, which 

 grow on soils derived from both sedi- 

 mentary and igneous rock. The Rocky 

 Mountain juniper prefers soils derived 

 from limestone. 



Temperatures in the pinyon-juniper 

 type of forest are about 5 lower than 

 in the grassland zone below and about 

 6 higher than in the ponderosa pine 



zone immediately above. The mean 

 maximum temperatures approximate 

 67; mean minimum, 37; and mean 

 annual, 52. The growing season is 

 longer than in the ponderosa pine for- 

 est. Winters are not so severe, and 

 snows do not get so deep. 



The pinyon-juniper forest contains 

 several species of pinyon and juniper 

 in varying mixture. 



Of the three species of pinyon in 

 Arizona and New Mexico, by far the 

 most abundant and most widely dis- 

 tributed is the Pinus edulis, commonly 

 called pinyon. Its short needles, usually 

 less than 2 inches long, occur two to 

 the bundle. It produces most of the 

 pinyon nuts collected locally for food 

 and for sale. 



The other species are of less impor- 

 tance. The one-needle pinyon (Pinus 

 monophylla) has only one needle to the 

 bundle. The Mexican pinyon (Pinus 

 cembroides), also of limited occur- 

 rence, has two or three needles to the 

 bundle. 



The pinyons are relatively small 

 trees, rarely more than 35 feet tall. 

 They have short, quite limby boles. 

 They are usually less than 2 feet in 

 diameter. 



Four species of juniper, locally called 

 cedars, occur in various parts of the 

 pinyon-juniper type. 



The one-seed juniper (Juniperus 

 monosperma) is a small, short-boled 

 tree, which branches into a broad, 

 spreading top almost from the ground 

 level. It is usually found on the drier 

 sites and at the lower edge of the type. 

 Normally it is the first tree species that 

 one sees as he goes from the lower to 

 the higher elevations. 



The Utah juniper (Juniperus utah- 

 ensis), also short, rarely exceeds 20 

 feet in height and 2 feet in diameter. 

 The trunk is fairly free of branches, 

 which usually are less than 6 feet long. 



The alligator juniper (Juniperus 

 pachyphloea) , so named because the 

 bark on the mature tree is so broken 

 that it resembles the back of an alli- 

 gator, is the tallest of the local junipers. 

 Sometimes it reaches a height of 60 



