NORWAY PINE IN THE LAKE STATES. 
23 
Column 2 of Table 13, which shows the age of trees of each diam- 
eter, was taken from Table 7, using the average figures of growth in 
the middle column of dominant trees. Much larger yields would 
have been indicated had the left-hand column been made the basis 
of the calculation. 
Column 3 was obtained from Table 10, volume growth of Norway 
pine, Table 7, middle column, for diameter growth of dominant trees, 
and from Table 4, average height based on diameter of dominant 
trees. 
Column 4 was obtained by squaring the crowns of trees of all 
diameter classes, computing the number of trees per acre for each 
class by dividing 43,560 by the square of the diameter of the crown, 
a density factor of 0.78 per cent, and then plotting the results and 
evening off by a curve for each diameter class. 
Column 5 was obtained by multiplying column 3 by column 4. 
Table 14 shows by decades the yields given in Table 13. 
Table 14. — Theoretical yield per acre of fully stocked stands, Quality I. 
Age 
(years). 
Yields 
(board 
feet). 
Age 
(years). 
Yields 
(board 
feet). 
50 
60 
70 
80 
90 
100 
110 
120 
8,400 
14, 600 
22, 000 
27, 600 
33,000 
37,700 
42,300 
46,500 
130 
140 
150 
160 
170 
180 
190 
200 
50,400 
54,000 
57, 600 
61,000 
64,000 
66, 900 
69,500 
72,000 
These theoretical yields agree with those found by actual measure- 
ments of fully stocked stands on first quality sites. The actual 
yields slightly exceed those shown in Table 14, notably for the ages 
from 110 to 160 years. At 170 years the actual yields fall off rapidly, 
while the yields computed from crown space continue to increase even 
after the results are reduced by a curve. These facts indicate, first, 
that the rate of growth used in the calculation is actually attained 
by the greater number of trees forming a Norway pine stand on 
good soil, and, second, that the density of the crowns of such stands 
is greater than 0.78, which is the assumed factor of density obtained 
by squaring the crowns which are normally round. Finally, the 
divergence of yields for 170 years clearly indicates that at this age 
the natural stands begin to deteriorate and do not maintain the 
closed canopy. The decrease in the number of trees per acre re- 
sulting from this process of deterioration lowers the yield from then 
on. Individual Norway pines will live to be 300 years old, but plots 
much over 200 years old are composed either of the remnants of 
much denser stands or of the survivors of a struggle with jack pine. 
