RATE OF GROWTH OF ARIZONA YELLOW PINE 699 



at 6,000 feet there were 53 trees of Chihuahua pine, 23 junipers, and 

 3 pinons (Piuus cciubroides), as well as a number of oaks, which were 

 not enumerated. 



The trees which are associated with the yellow pine are represented 

 in all of the areas by seedlings and juveniles in proportions approxi- 

 mately like those given for the adults. Figures i, 2, and 3 give a 

 picture of the comparative representation of the age classes at the dif- 

 ferent altitudes, the 2.5-5 cm. class having been combined with the 



Fig. 2. — Graphs showing total number of young trees from 2.5 to 10 cm. in diameter on 

 ■six areas at four altitudes. Hatched portions indicate species other than Arizona yellow pine. 



5-10 cm. class. In all of these figures the shaded portions of the 

 graphs indicate the associated species and the white portions refer to 

 yellow pine. The enormous number of juveniles on the south- facing 

 area at 7,000 feet (fig. i) was due to very young seedlings of yellow 

 pine that had not yet passed the age at which mortality ceases to be very 

 high. The condition on this area at the time of enumeration is one 

 that frequently occurs at all elevations resulting from a good seed crop 

 and good conditions for germination. The decimation of such an 

 abundant stand of seedlings is due chiefly to the low soil moisture of 



