LIFE HISTORY OF LODGEPOLE PINE IN EOCKY MOUNTAINS. 33 



It should be noted that these normal yields represent the best that 

 have been found in unmanaged virgin forests, not the best which it 

 is theoretically possible to obtain under proper methods of forest 

 management. Table 2, for example, shows that a dominant tree at 

 the age of 140 years is able to reach a diameter of about 12 inches 

 and a height of about 75 feet, with a volume of 120 board feet. To 

 determine in an approximate way how many trees could be produced 

 per acre with the right kind of thinnings at proper intervals, the 

 average space in the stand occupied by a tree of this size was meas- 



l ured in a number of instances and found to average approximately 

 166 square feet. At this rate there should be 262 such trees per acre, 



i with a yield of 31,400 board feet, which is 19 per cent greater than 

 that given in the table of normal yield for 140-year-old stands on 

 the best sites. While it is probable that such a yield could seldom 

 be obtained even under intensive management, the illustration serves 

 to show the possibility of securing better results with improved 

 spacing. 



EFFECT OF THINNING. 



The marked effect which thinnings often have in increasing the 

 rate of growth of individual trees is also notable in the case of 

 stands. This effect is seen in a number of cut-over areas on the Deer- 

 lodge Forest which were culled from 13 to 25 years ago. In every 

 case the loggers removed only such timber as suited their purpose, in 

 some cases taking the larger material for ties, in others, removing the 

 smaller trees for fence posts. Some of the trees left had thrifty 

 crowns, and for this reason could be expected to benefit from the 

 increased light ; while others were very badly suppressed, with small 

 crowns, and could hardly be expected to accelerate their growth to 

 any extent. In collecting the data summarized in Table 10, average 

 trees were selected for measurement irrespective of the probability of 

 their showing an increase in the rate of growth. The various periods 

 which had elapsed since the different cuttings were made averaged 

 20 years, and for purposes of comparison the figures were all worked 

 up on the assumption that the cutting was done just 20 years before 

 the date of the investigation. 



