22 



BULLETIN 139, U. S. DEPARTMENT OP AGEICULTURE. 



Table 12. — The crown width of dominant trees on basis of diameter breast-high, Itasca 



County, Minn. 



[Based on 134 measurements.] 



Diameter 



Width of 



Diameter 



Width of 



breast-high 



crown 



breast-high 



crown 



(inches). 



(feet). 



(inches). 



(feet). 



3 



4 



13 



15 



4 



5 



14 



15 



5 



7 



IS 



16 



6 



8 



16 



16 



7 



9 



17 



16 



8 



11 



18 



16 



9 



12 



19 



16 



10 



13 



20 



17 1 



11 



13 



21 



12 



14 







The crowns of Norway pine trees are remarkably narrow com- 

 pared with those of southern and western pines, which makes possible 

 a larger number of trees per acre. An idea of the possible approx- 

 imate yields which may be obtained under management is given in 

 Tables 13 and 14. It can be assumed that with frequent thinnings 

 the trees remaining in the stand will grow at the average rate of 

 dominant trees and will have the width of crown indicated in Table 

 12. Assuming that the average volume of these trees will be that 

 shown in Table 10, it is necessary only to know the average number 

 of trees per acre in order to ascertain roughly the yield of such stands 

 at a specified age. 



The diameter of the average crown was squared in finding the 

 number of such trees that could stand on an acre. Since Crowns 

 are circular, this introduced a factor of safety amounting to a reduc- 

 tion of 22 per cent of the number of trees which might otherwise be 

 computed as having growing space, and gives a crown density of 78 

 per cent instead of 100 per cent. 



Table 13. 



Yields per acre of dominant trees, calculated from diameter growth, average 

 crown space, and number of trees per acre at different ages. 









Trees per 





Diameter 



breast-high 



(inches). 



Age 

 (years). 



Volume of 

 tree. 



acre from 

 curve, 



based on 

 crown 

 space. 



Yields per 

 acre. 







Board feet. 



Number. 



Board feet. 



8 



49 



23 



302 



8,280 



9 



56 



45 



266 



13, 590 



10 



63 



67 



241 



17,822 



11 



71 



94 



221 



22, 654 



12 



80 



128 



206 



28, 288 



13 



90 



160 



193 



32, 960 



14 



101 



197 



183 



38, 021 



15 



114 



242 



175 



44, 286 



16 



128 



289 



168 



50, 575 



17 



145 



329 



163 



55, 272 



18 



163 



383 



158 



62, 429 



19 



182 



444 



154 



70, 152 



20 



200 



505 



151 



77, 770 



