3160 Chapter 26 



Tree wood specific gravity (based on ovendry weight and green volume) 

 ranges from 0.40 in yellow-poplar to 0.66 in post and white oaks. Tree bark, 

 which constitutes about 18.8 percent of above-ground biomass (foliage except- 

 ed) in 6-inch trees, ranges in specific gravity from 0.34 in winged elm to 0.64 in 

 blackjack and northern red oaks (table 7-7). In-place densities of wood are given 

 in table 7-2 and those of bark in table 13-40. Bulk densities of particulate fuels in 

 various forms are given in section 16-13, in table 13-42, and in related 

 discussion. 



Moisture content of stemwood of 22 of the species arithmetically averages 

 73.5 percent of ovendry weight (42 percent wet basis); bark averages 67.2 

 percent moisture content on a dry basis and 40 percent on a wet basis (table 8-2). 

 Stemwood of sweetgum has highest moisture content at 120.4 percent of 

 ovendry weight (55 percent on a wet basis) and stembark of yellow-poplar has 

 highest moisture content at 125.8 percent of ovendry weight (56 percent on a wet 

 basis). Moisture content of bark residues is discussed in section 13-4. 



In general, large piles of wood chips or bark stored outside in the South gain 

 moisture content (see sections 16-16, 16-17, and 13-4). Shallow piles, a foot or 

 less in depth, can be airdried, however, if under cover and turned frequently 

 (figs. 20-18AB). 



Heats of combustion of stemwood, stembark, branchwood, and branchbark 

 all range between 6,840 and 8,183 Btu per ovendry pound (table 9-12). The 

 averages are as follows: 



Heat of combustion 

 Tree portion (higher heating value) 



Btulovendry pound 



Stembark 7,593 



Branchbark 7,623 



Branchwood 7,784 



Stemwood 7,827 



Additional data on heat of combustion of wood of the pine site hardwoods are 

 found in section 9-3 under the subsection HEAT OF COMBUSION; data on 

 bark are found in section 13-6 under the subsection HEAT OF COMBUSTION. 

 Figure 11-3 relates heat of combustion in wood-bark residue piles to time in 

 storage, and indicates that heat content per ovendry pound increases during 4 

 months of storage. 



About 50 percent of the wood and bark of these hardwoods is comprised of the 

 element carbon, from 30 to 44 percent is oxygen, and about 6 percent is 

 hydrogen. Together, ash and nitrogen amount to about 1 percent of wood 

 weight; ash content of bark is higher than that of wood (table 26-3). 



The proximate analyses for wood and bark also fall within a rather narrow 

 range of values (table 26-4). In general, when wood and bark are burned, 75 to 

 80 percent will bum in the gaseous state whil6 about 20 to 24 percent will bum as 

 fixed carbon (Arola 1976). 



