28 BULLETIN 460, U. S. DEPARTMENT OF AGRICULTURE. 
grades of it are suitable for many, if not all, of the commercial uses 
to which western yellow pine is put. Only very limited local use is 
made of this wood for lumber?+ in Arizona, chiefly because the tree 
grows in rough situations difficult of access. 
OCCURRENCE AND HABITS. 
Pinus arizonica occurs on dry rocky and gravelly slopes, canyon 
sides, and ridges at elevations between 6,000 and 8,500 feet (map 
No. 9). It often forms pure, quite dense stands of good saw timber 
at the lower elevations where the soil is less rocky, while at higher 
levels it grows in open scattered stands of poor form for timber. 
- Sometimes it is associated with western yellow pine, Apache pine, 
and occasionally with Chihuahua pine, Arizona cypress, and white- 
leaf oak. 
Arizona pine is intolerant of heavy shade during all periods of 
its growth, being similar in this respect to the western yellow pine. 
Seedlings, however, grow well under very light shade for 3 or 4 
years. This species bears seed abundantly about every 2 years, but 
as a rule germination occurs only sparingly in the rougher, rockier 
situations, though plentifully on broken, exposed mineral soil. 
LONGEVITY. 
Arizona pine is probably a rather long-lived tree, attaining an 
age of at least 250 or 300 years. The hmited number of trees studied 
show that those from 20 to 30 inches in diameter are from 115 to 
165 years old. Further determinations are necessary, however, to 
establish the actual limits of age. 
WESTERN YELLOW PINE. 
Pinus ponderosa Lawson. 
COMMON NAME AND EARLY HISTORY. 
Throughout its wide distribution this tree is generally known as 
“-vellow pine” but sometimes as “ bull pine.” In order to avoid con- 
fusion of Pinus ponderosa with other “ yellow ” pines it became neces- 
sary to adopt the common name western yellow pine, which is now 
accepted quite widely by lumbermen. The technical name Pinus 
ponderosa, Which most authors apply only to the big yellow pine of 
the Pacific slope, is here made to include also the Rocky Mountain 
Mexico, along with other hard-wooded and soft-wooded pines. Specimens collected by 
American prospecting timber operators usually contain Arizona pine, reported +o be asso- 
ciated with other Mexican timber pines, 
