RATE OF GROWTH OF ARIZONA YELLOW PINE 697 



After securing the data regarding the climatic conditions of the 

 Santa Catahna Mountains, and after correlating the distributional feat- 

 ures of the vegetation with these data, it seemed desirable to make a 

 further correlation between the climatic gradients and some physiologi- 

 cal feature of one or more plants. Since the Arizona yellow pine is the 

 predominant plant through 4,000 feet of elevation, and is easily counted, 

 measured, and studied, it was chosen for an investigation of this char- 

 acter. The results given in this paper are designed to show the differ- 

 ences in population in this tree as growing at different altitudes, the 

 differences in the character of the populations, and the differences or 

 similarities in the rate of growth at the several elevations. The data 

 which it is possible to present at this time are extremely meager, par- 

 ticularly from the standpoint of the forester, who is accustomed to 

 working with large quantities of figures regarding the age of trees and 

 the populations of given areas. The practical conditions under which 

 the work was done made it impossible, however, to do more than secure 

 the data embodied in this paper, which are presented more in the hope 

 that they will be suggestive than with the feeling that they are either 

 exhaustive or final. 



For the purpose of the study of populations and rate of growth, six 

 areas were selected, each one hectare in size. Two of these areas were 

 located on north and south slopes in Bear Cafion, at an elevation of 

 6,000 feet. Two of them were located in Rose Creek, on north and 

 south slopes, at an elevation of 7,000 feet. One was located on a south 

 slope in Marshall Gulch, at 8,000 feet, and one was located at 9,000 feet 

 on the south face of Mt. Lemmon. There are no areas of yellow pine 

 at elevations below 6,000 feet, and this pine forms only a small part of 

 the forest on northern slopes at 8,000 and 9,000 feet. These areas were 

 selected as being typical of six distinct habitats in which the tree is 

 found, in all of which instrumentation had been carried on. Consider- 

 able care was taken in the selection of the exact areas for study in an 

 effort to secure slopes of uniform inclination, areas in which soil con- 

 ditions were similar, and stands of pine that appeared to exhibit the 



Table 3. — General Diameter Classes of All Species of Trees on Six Areas 

 Investigated in the Santa Catalina Mountains, of Altitude and 



Slope Exposure as Indicated 

 Station 0-2.5 cm. 2.5-5 cm. 5-10 cm. 10 + cm. Total 



9.000 S 2,525 519 139 352 3,183 



8,000 S 909 23 8 202 1,142 



7,000 S 5,876 19 10 131 6,036 



7,000 N 755 6 50 233 1,044 



6,000 vS 138 19 62 249 468 



6,000 N 1,212 20 16 124 1,372 



