CHARCOAL FROM CHEMI-PEELED HARDWOODS 

No. 94 

1959 

Removing bark from standing trees with sodium arsenite is an inexpensive but efficient way to produce peeled 

pulpwood. About 200,000 cords, principally hardwoods, are 

produced annually by chemi-peeling, a technique that is fast 

replacing old-fashioned sap-peeling as a means of debarking 

in the woods. 

It appeared that chemical bark removal might be helpful in other fields of hardwood utilization, particularly 

where very low-grade trees could be used. The production of 

charcoal is one of these, a form of utilization that is being stimulated by the increasing popularity of outdoor cooking. Because tree quality is generally not a limiting factor, the charcoal market provides an outlet for hardwoods 

that occupy valuable growing space but are difficult to convert profitably to other products. The chemical treatment 

itself is easy and economical; publications on the subject 

by Curtis (1956), Wilcox et al. (1956), and others are 

available. 

Charcoal wood is usually prepared in this way: the 

trees are cut and bucked to length, and the wood is moved to 

storage yards for about 12 months' seasoning. Another handling is then required to load it into a kiln. These operations use considerable labor; also, to store enough wood to 

operate the kiln at full capacity requires considerable 

space. So, any changes in procedure reducing these requirements would tend to increase profits, or possibly permit 

paying a little more for the wood. 

Some of these handling and storage requirements might 

be overcome by the simple expedient of chemi-peeling the 

standing trees and "storingw the wood about a year on the 

stump. Then, assuming adequate seasoning had occurred, the 

trees could be felled, bucked, transported to the kiln, and 

loaded directly, thus saving one handling. Storing wood in 

this fashion would also reduce the risk of losses from fire, 

decay, and theft. Furthermore, removal of the bark permits 

loading kilns with a larger volume of solid wood. 
Observations in the Adirondacks indicate that chemically debarked trees can stand in that area for several 

years without appreciable deterioration (Rushmore, 1959). 

Susceptibility to decay varies with species and climate, 

tending generally to increase southward with the lengthening 

of the warm season. Where possible, stump storage for more 

than 1 year would permit the stockpiling of larger volumes 

of wood, and might result in better seasoning. 

The Study 

A small study was conducted at the Beltsville Experimental Forest in Maryland to test the practicability of 

chemi-peeling, storing on the stump, and trucking directly 

to the kiln in a charcoal operation. The trees in a poorsite stand of oaks were treated in early summer by applying 

sodium arsenite solution copiously to wide basal bark girdles. The trees, of several species representing both red 

and white oak groups, averaged 9 inches d.b.h. and, though 

of poor form and quality, were well suited for charcoal 

production. 

Fourteen months after treatment, when much of the 

bark had loosened, the trees were felled and bucked into 5- 

foot lengths, and the wood was trucked to and loaded into a 

cinder-block kiln. The charcoal produced from this peeled 

wood was compared in yields and general quality with that' 

made from the usual run of unpeeled wood. 

The kiln used in the study had a capacity of 548 

cubic feet of wood, gross measure, or 3.425 units of 160 

cubic feet. In comparing yields, all charges were considered 

to be to the full capacity of 3.425 units. 

Rough or unpeeled hardwoods were not actually cut and 

seasoned as part of the study. Data for this type of wood 

were obtained from several burns made by the kiln operator 

from his own stockpile just prior to firing the chemi-peeled 

wood. Both types of wood had been seasoned for about the 

same length of time. 

Results and Discussion 

The yield of charcoal was over 100 pounds greater per 

unit of peeled wood than for the same volume of rough wood 

(table 1). This yield increase of 11 percent is believed to 

be due principally to the absence of the bark, and the resultant higher volume of wood in the kiln charges. Although 

bark is converted to charcoal, it tends to increase the 

amount of fines and dust, thus affecting the yield of usable 

lump charcoal. And, because bark has a much higher mineral 

content than the wood, better quality, cleaner charcoal, 

with lower ash content, is produced from bark-free wood. 
Left: Applying sodium arsenite solution to wide bark girdle near 

base of a red oak tree. Center: A chemi-peeled hardwood stand 

1 year after treatment. Right: During stump storage, the bark 

cracks and loosens; this not only simplifies removal of bark but 

also hastens seasoning. 

Another reason for the higher yield may have been the 

lower moisture content of the peeled wood when burned (table 

1). Hicock et al. (1951) and others have found that, with a 

given species, yield of charcoal by weight increases as the 

moisture content of the wood decreases. 

A third factor that may have influenced charcoal 

yields was the difference in soundness of the peeled and the 

unpeeled wood. In the latter, after a year of air-seasoning 

in the yard, considerable sapwood decay had developed under 

the bark; this would tend to reduce yields. By contrast, 

the bark on the treated trees had cracked and loosened during stump storage, which in turn hastened surface drying and 

checking of the wood. Decay was much less advanced in these 

trees than in piled wood. These observations are in accord 

with those of Rushmore, previously cited. 

Based on a cost for the chemi-peeling treatment of 

$1.55 per rough unit (by tree measurement), and assuming an 

average bark volume of 15 percent, the treatment cost per 

unit of peeled wood was $1.82, with labor at $1.40 per hour. 

Charcoal presently brings from 2.5 to 3 cents per pound 

wholesale at the kiln. Thus, the value of the extra 100 

pounds of charcoal obtained from a unit of chemi-peeled wood 

more than offset cost of the treatment. 

Some question might arise concerning association of 

the toxic sodium arsenite with a product used in food preparation. In a special study (Wilcox et al., 1956), analyses 

of pulpwood from chemi-peeled trees showed a uniformly low 

arsenic content, well under the tolerance allowed for food. 

Even less should be present in charcoal after undergoing 

partial combustion during manufacture. 
Table 1.--Relative yield of charcoal from chemi-peeled 

and rough hardwoods 

Summary and Recommendations 

Type of 

wood 

Chemi-peeled and stump-seasoned hardwoods in this 

study yielded 11 percent more charcoal by weight than equivalent volumes of rough wood. Other advantages include: possible saving in wood handling; less risk of losses by fire, 

theft, and decay; less storage space required at the kiln; 

and, by eliminating bark, a general improvement in charcoal 

quality as well as a higher yield. 

Anyone with limited yard space for storing wood, or 

concerned about increasing charcoal yields and qua1 ity, 

might well consider using the chemi-peeling method of preparing his wood. Although this study dealt only with charcoal product ion, the advantages of chemi-peeling and stump 

storage would apply in general to other forms of round-wood 

utilization where peeling and seasoning are required. 

Units Pounds Percent 

Chemi-peeled 3.425 3,410 49 

Rough 3.425 3,062 6 5 

Average 

volume 

LITERATURE CITED 

Curtis, R. 0. 

1956. Estimating costs of improving Adirondack timber stands by 

killing culls with frills and sodium arsenite. U. S. Forest 

Serv. Northeast. Forest Expt. Sta. Forest Res. Note 63. 2 pp. 

r 

Average yield 

of charcoal 

Hicock, Henry W., et a1 . 1951. The Connecticut charcoal kiln. 

Conn. Agr. Expt. Sta. Bul. 431. 48 pp., illus. Storrs, Conn. 

Moisture content of 

wood when burned 

Rushmore, Francis M. 

1959. Some effects of silvicides on hardwoods. 

Soc. Amer. Foresters N.Y. Sect., N.Y. Forester 16 (1): 5-6. 

Wilcox, Hugh, et al. 

1956. Chemical debarking of some pulpwood species. 

State Univ. N.Y. Coll. Forestry Tech. Pub. 77. 43 pp., illus. 

Research Forester) Laurel Research Center 

Northeastern Forest Experiment Station 

Forest Service, U.S. Dept. Agriculture 

AGRICULTURE-FOREST SERVICE-UPPER DARBY