THE CALCULATION OF THE MEAN FIBER-LENGTH OF 

 A TREE 



Bv W. B. Stokes 



Forest Products Laboratories of Canada, Montreal 



In finding the mean length of the fibers of a tree it has been found 

 convenient to cut cHscs or cross-sections at certain distances along the 

 felled trunk, thus obtaining sample layers which were at definite 

 heights from the ground in the standing tree. 



The volume of wood to be represented by each disc can be esti- 

 mated fairly accurately. It might be assumed, for instance, that the 

 disc represented half the length of the bolt above it and half that of 

 the bolt below it. If the product of every volume into the mean fiber- 

 length of its representative disc be obtained, and the sum of all such 

 products be divided by the total volume of wood, the quotient will be 

 the mean fiber-length for the tree. 



The determination of the true mean fiber-length of the disc is the 

 most serious operation in this procedure. Usually the mean fiber- 

 length is not the only object of such a series of operations. The 

 variation in fiber-length throughout the tree is also a matter of im- 

 portance. The length of fibers varies according to their height in 

 the tree. Most notable, however, is the variation which takes place 

 as the tree grows older. Taking such a disc as has been referred to 

 one finds that the wood next the pith has the shortest fibers and that 

 the fiber-length increases as one proceeds towards the bark. If the 

 tree is an old mature specimen this variation in fiber-length may cease 

 to be an increase and may even become a slight decrease before the 

 bark is reached. Indeed one may say that a mature tree is one whose 

 recently added fibers are no longer than those laid down in previous 

 seasons. 



In taking samples of wood from the discs it has been customary to 

 remove these from certain positions along a radius having the pith as ■ 

 center. The positions are chosen according to their distances from 

 the pith or from the bark, these distances being measured either in 

 inches or by the number of annual rings. Usually, however, the dis- 

 tance of a sample from the pith in inches is known. 



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