REPRODUCTION OF WESTERN YELLOW PINE. 75 



everything down to 11 inches diameter breast high was felled. The 

 area was not left as open as might be expected, because of the pres- 

 ence of groups of young unmerchantable pine and of Gambel oak. 

 All of the reserved trees were selected with special reference to 

 capacity for seed production. Windfirmness, good crown develop- 

 ment, and general vigor were the primary qualifications. As far as 

 possible they were distributed uniformly and singly, although oc- 

 casionally 2 or even 3 were left in a group. Table 19 shows that 75 

 per cent of the seed trees on this area are over 20 inches in diameter. 



(3) Shelterwood. — As this cutting was actually carried out. it does 

 not conform to the specifications of the shelterwood system. It 

 differs from the group-selection method only in leaving more ma- 

 ture trees. The volume after cutting, as shown by Table 19, was 

 6,600 feet b. in., or three times as great as on the group-selection 

 area. Since this excess volume is made up almost entirely of large 

 trees, and since yellow pine stands are very open to begin with, 

 the appearance of the two stands after cutting does not suggest 

 any radical difference in silvicultural practice. 



The three cutting areas are contiguous and similar in topography, 

 soil, and vegetation. The group selection and scattered seed-tree 

 divisions each contain 160 acres, and the shelterwood division 112 

 acres. A shallow, stony, clay soil, derived from basalt, predominates. 

 Three rather distinct qualities of site are recognized: (1) flats or 

 valleys with alluvial soil 18 to 24 inches deep, practically free of 

 stones, ground cover mainly Festuca arizonica; (2) lower slopes, soil 

 12 to 18 inches deep, more stony than (1), ground cover mainly bunch 

 grasses (Muhleiibergia nwntana and Festuca arizcmica) ; and (3) 

 upper slopes and mesas with soil seldom exceeding 6 inches deep, 

 surface very stony, ground cover mainly black sporobolus (Sporo- 

 bolus mterruptus). 



At the time these areas were established, in 1913, seedlings from 

 10 to 15 years old. mostly damaged by sheep, occurred in scattered 

 clumps, mainly on site 2. There were also a considerable number 

 of 2-year-old seedlings, nearly all of which died in the succeeding 

 2 years, partly as a result of injury by sheep. 



Seven plots of from 2 to 4 acres each were selected within each 

 cutting division for studying reproduction and other problems. 

 They are distributed so as to represent all the site qualities. Each 

 plot was mapped as illustrated by Figure 1. During the summer 

 of 1919 two sheep-proof fences were built so as to include three re- 

 production plots within each cutting area. 



Considering the representative character of the sample plots 

 within the various cutting divisions and the relatively large area 

 covered by seedling counts, we should expect the initial number 

 of seedlings to be in some measure proportional to the number of 



