LIFE HISTORY OF LODGEPOLE PINE IN ROCKY 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- 
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, 
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. 
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