THE COMPOSITE TYPE ON THE APACHE 

 NATIONAL FOREST. 



OBJECT OF THE STUDY. 



A very unusual forest type in which western yellow pine, Douglas 

 fir, and Colorado blue spruce occur in mixture has been found to exist 

 in certain localities on the Apache and adjacent National Forests in 

 southern Arizona. While western yellow pine (Pinus ponderosa 

 Laws) and Douglas fir (Pseudotsuga tei/bZia (Lam.) Brit ton) are both 

 common throughout the Southwest, and are often found in mixture, 

 the presence of Colorado blue spruce (Picea parry ana (Andre) Parry), 

 and especially its occurrence with western yellow pine, is extraordinary. 

 Formerly this species was thought to grow only in the central Rocky 

 Mountain States, for the most part along stream courses, and seldom 

 in commercial quantities. Here, however, instead of growing 

 typically along streams or in canyons, it is found on level or nearly 

 level areas, mixed in varying proportion with western yellow pine and 

 Douglas fir. The growth, side by side, of two species differing so widely 

 in their requirements as blue spruce and western yellow pine points to 

 unusual ecological conditions. This report, however, deals with 

 growth, and no attempt will be made to explain the ecological factors 

 responsible for the type. The study of the type, the results of which 

 are given in this bulletin, was made in order that a plan of manage- 

 ment for it could be included in the working plan for the forest. 



THE TYPE. 

 EXTENT AND COMPOSITION. 



The type is found mainly between altitudes of 8,750 and 9,200 

 feet, on the Blue and White Mountain Ranges of Arizona. The 

 altitudinal limits are rather sharply defined, and a slight variation 

 from them, with the accompanying change in temperature and rain- 

 fall, will completely change the type. Thus, below 8,750 feet the 

 Douglas fir and spruce are almost entirely lacking, and the yellow pine 

 grows in pure stand. Above 9,200 feet western yellow pine is seldom 

 found, but Douglas fir and blue spruce are the prevailing species, 

 either in mixture or in pure stands. Likewise, a difference in ex- 

 posure or even in degree of slope within the limits of the type will 

 cause a marked change. A sharp south slope, even toward the type's 

 upper limits, will often be completely covered with western yellow 

 pine, while a northern exposure near the lower limits may have a 

 cover of spruce or fir with little or no western yellow pine. 



