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. 



