3326 Chapter 27 



In a study of tops left after saw log harvesting, Wartluft (1978) found that bark 

 accounted for an average of 23 percent of the green top weight. Some species of 

 interest were: 



Bark moisture content Bark proportion 

 Species No. of trees (ovendry basis) of green weight 



Percent 



Ash, sp 1 49 19 



Hickory sp 2 40 26 



Oak, chestnut 16 55 25 



Oak, red sp 31 67 20 



Oak, white 6 48 22 



Tupelo, black 3 89 24 



Yellow-poplar 14 81 28 



Hard hardwoods 57 59 22 



Soft hardwoods 18 81 27 



Data on bark moisture content are in section 13-4, and bark specific gravity 

 data are in section 13-6. Bark bulk density is discussed in the paragraph Bulk 

 density of bark residue in subsection SPECIFIC GRAVITY of section 13-6 

 (Page 1208). 



Bark thickness data are in section 13-2 (Page 1124). 



Bark thickness and tree diameter growth. — Foresters generally estimate 

 tree diameter growth by taking increment cores at breast height to measure the 

 rate of wood growth and by assuming that bark thickness remains constant. 

 However, bark slowly increases in thickness over the years; so such estimates 

 can be up to 17 percent low (McCormack 1955). To solve this problem, McCor- 

 mack (1955) provides growth factors for several hardwood species measured in 

 the Southeast (table 27-141). Note that this factor includes a multiplier of 2, 

 which accounts for two bark thicknesses. One simply multiplies the measured 

 radial wood growth for the period (as obtained by increment core) by the growth 

 factor for that species to obtain total diameter growth. For examle, if we assume 

 a 10-year radial wood growth measurement of 1. 1 inches for a post oak that is 

 now 13.2 inches in diameter, then the total diameter growth including bark is 



(1.1)(2.19) = 2.4 inches 



The outside bark diameter of the tree at the beginning of the period would be 

 computed as follows: 



13.2 - 2.4 = 10.8 inches 



If no allowance were made for increase in bark thickness, the original diameter 

 of the tree would be estimated at 11 inches, i.e., (13.2) - (2)(1.1) = 11, and 

 actual tree diameter growth would be underestimated by 8 percent. 



MILL RESIDUES— PROPORTION OF LOG VOLUME 



Utilization of stems and logs varies greatly among mills and according to 

 product manufactured. For example, fiberboard plants producing hardboard 

 from whole-tree chips convert a high proportion of tree volume to primary 

 product, whereas plants making hardwood flooring (fig. 22-1) or barrel staves 



