REPRODUCTION OF WESTERN YELLOW PINE 



285 



respectively for plot 2. The increment per cents exhibit a correspond- 

 ing relation. A portion of the excess increment on plot 2 is accounted 

 for by the entrance of new trees. During the 5-year period covered, 

 the mean increase in number of trees 12 inches and over in diameter 

 per acre was 1.18 on plot 2, against 0.23 on plot i. The difference in 

 trees below 12 inches is still greater, although these trees do not enter 

 into the board-foot volumes, and since most of them are in the 4 and 

 5 inch classes they do not represent a great cubic increment. Possibly 

 a portion of the difference in growth rate is attributable to site quality. 

 The health of the stands is probably another factor. These are sub- 

 jects which require further investigation. 



Table 5. — Increment 



[Board measure includes trees 12 inches and over, d. b. h. 

 includes trees 4 inches and over, d. b. h.] 



Cubic measure 



a Board measure, Scribner Decimal C Scale. 



.Another subject on which this study is expected to throw light is 

 the effect of distribution upon growth. On all of the plots the great 

 majority of the trees occur in dense, practically even-aged groups 

 separated by large openings. Records on "intensive" plots show al- 

 most invariably a much greater diameter growth for trees in the open 

 than ff)r trees in large groups. Continued records will probably prove 



