20 



BULLETIN 139, U. S. DEPARTMENT OF AGRICULTURE. 



with a table in volumes for trees of different diameters and heights. 

 The table indicates that Norway pine grows in volume at a uniform 

 rate to an advanced age. 



Table 10. — Growth in volume, on basis of age, of average dominant trees, Cass County, 



Minn. 



Age 

 (years). 



Diameter. 



Height. 



Volume. 



Scribner 



rule. 



Periodic growth for 

 10-year periods. 



Mean annual growth. 





Inches. 



Feet. 



Cubic feet. 



Board feet. 



Cubic feet. 



Board feet. 



Cubic feet. 



Board feet. 



10 



0.8 



8 















20 



2 8 



21 















30 



4 9 



35 



2.3 









0.77 





40 



6 6 



47 



5.3 





3.0 





.133 





50 



8 2 



58 



10. 1 



27 



4.8 





.202 



0.54 



60 



9.6 



66 



15.8 



57 



5.7 



30 



.263 



.96 



70 



10.9 



72 



21.1 



90 



5.3 



33 



.301 



1.29 



80 



12.0 



76 



27.4 



128 



6.3 



38 



.343 



1.60 



90 



13.0 



80 



34.0 



160 



6.6 



32 



.355 



1.77 



100 



13.9 



83 



40.6 



193 



6.6 



33 



.406 



1.93 



110 



14.7 



85 



46.3 



22S 



5.7 



35 



.421 



2.08 



120 



15.5 



87 



53.8 



263 



6.5 



35 



.448 



2.19 



130 



16.1 



88 



59.0 



286 



5.2 



33 



.454 



2.20 



140 



16.7 



89 



63.6 



314 



4.6 



28 



.454 



2.25 



150 



17.3 



90 



69.4 



345 



5.8 



31 



.463 



2.30 



160 



17.8 



91 



74.4 



374 



5.0 



29 



.465 



2.34 



170 



18.4 



91 



79.3 



405 



4.9 



31 



.465 



2.39 



180 



18.9 



92 



84.4 



437 



5.1 



32 



.469 



2.43 



190 



19.5 



92 



89.3 



470 



4.9 



33 



.470 



2.47 



200 



20.0 



93 



94. 6 



505 



5.3 



• 35 



.473 



2.52 



The growth in diameter, height, and volume of individual Norway 

 pine trees is of little aid in determining the yield per acre. Yields of 

 stands of different ages are best found by actual measurements of 

 stands of the age to be recorded. The yield of even-aged stands is 

 then determined by ., multiplying the volume of the average, tree by 

 the number of trees on the area. The sample plots upon which 

 Table 11 is based were located in Cass and Itasca Counties, Minn. 

 The plots selected for measurement were completely stocked with 

 pine. A mature and fully stocked Norway pine stand forms a prac- 

 tically complete crown cover. The crowns themselves are not dense 

 nor is the shade deep, though it is usually sufficient to exclude from 

 the dry and sandy forest floor practically all underbrush, leaving only 

 a carpet of needles. At the age of 150 years, however, the stand 

 begins to thin out, and by 200 years the canopy will be broken, with 

 many blanks caused by the death of trees. The yield per acre at 

 this time is actually less than at an earlier age. 



The method followed in constructing Table 11 was to plot the 

 yield of each sample plot on cross-section paper, -on the basis of age. 

 The space between the maximum and minimum curves was then 

 divided into three parts, representing good, medium, and poor yields. 

 These coincide roughly with the three qualities of soils upon which 

 the plots were taken. A curve was then drawn through the center 

 of each space representing the qualities, from which the yields for each 

 age were read. In applying this table it should be remembered that 

 the figures represent a theoretically perfect stand. Actual yields on 



