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JOURNAL OF FORESTRY 



average conditions of reproduction for that region. On each of these 

 areas the entire population was counted, including seedling trees, and 

 the diameter of each of the trees lo cm. and over in diameter was meas- 

 ured. After this enumeration a number of trees were cut in each area 

 and their ages determined by ring count. The figures for the total pop- 

 ulations of the six areas are given in Table 3. The individuals were 

 grouped into four-size classes: 0-2.5 cm., 2.5-5 cm., 5-10 cm., and 

 10 cm. or over. The trees 10 cm. and over in size, which will be desig- 



FiG. I. — Graphs showing total number of seedling trees up to 2.5 cm. in diameter on sLx 

 areas at four altitudes, the slope exposure being indicated by S. and X. Hatched portions 

 indicate species other than Arizona yellow pine. 



nated as the adults, were measured breasthigh, the juvenile classes 

 being measured 5 cm. from the ground. The total number of adults at 

 9,000 feet includes 36 trees of Mexican white pine (Pwiis strobiformis) 

 and one of Douglas fir (Pseudotsuga mucronaia). At 8,000 feet there 

 were 20 adult Mexican white pines. On the south-facing area at 7,000 

 feet all the adults were yellow pine, while on the north-facing area at 

 that elevation there were 23 Douglas firs and 16 white pines. On the 

 north-facing area at 6,000 feet there were two adult junipers {Junipe- 

 rus pachyphloca), with one Douglas fir, while on the south-facing area 



