HONEYCOMB AND RING FAILURE IN BACTERIALLY INFECTED RED OAK LUMBER

AFTER KILN DRYING

FPL 165 1972

U.S.D.A. FOREST SERVICE RESEARCH PAPER

U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, Madison, Wisconsin

ABSTRACT

Northern red oak (Quercus rubra L.) lumber from trees with heartwood infected by certain anaerobic bacteria proved more susceptible to honeycomb and ring failure during kiln drying than similar lumber from non-infected heartwood. Before drying, infected heartwood that was sound and clear of stains appeared the same a s non-infected heartwood. However, the in­fected wood could be distinguished from non-infected green wood by having abnormal sour vinegar and ran­cid odors which result from volatile fatty acid produc­tion by the anaerobic bacteria.

Two charges of 1-1/8-inch-thick boards, from six trees growing on a good site, were kiln-dried green from the saw under mild and accelerated schedules, Boards of five Standard grades--FAS, Selects, No. 1 Common, No. 2 Common, and No. 3 Common--were included in each charge. Zones of bacterially infected heartwood could be found in all grades of lumber from infected trees but were more prevalent in the lower lumber grades.

Honeycomb and ring failure occurred in bacterially infected heartwood dried under both schedules, but this degrade was more severe in the faster dried material. The loss from honeycomb and ring failure in infected boards grading No. 1Common and Better was 6.5 per­cent for the mild schedule and 23.7 percent for the accelerated schedule. No loss was detected in non­infected boards grading No. 1 Common and Better dried under either the mild or accelerated conditions.

The implication of this work is that it would be possible to speed up the drying of red oak without increasing losses from honeycomb and ring failure if boards containing these bacterial infections can be sorted out and dried separately.

HONEYCOMB AND RING FAILURE IN BACTERIALLY

INFECTED RED OAK LUMBER AFTER KILN DRYING

By

J. C. WARD, Forest Products Technologist R. A. HANN, Forest Products Technologist R. C. BALTES, Physical Science Technician and E. H. BULGRIN, Forest Products Technologist

Forest Products Laboratory, Forest Service U.S. Department of Agriculture

— — —

INTRODUCTION

The kiln drying of oak lumber green from the saw can often present a perplexing problem, be­cause honeycomb and ring failure may occur in clear, apparently sound lumber under relatively mild drying conditions.

Honeycomb is an internal void caused by check­ing across the grain, while ring failure is an inter­nal void parallel to the annual ring. Certain refrac­tory hardwoods, especially the oaks, will usually honeycomb and sometimes develop ring failure under excessive temperature conditions (Ras­mussen 1961),1 but the problem considered in this paper occurs under recommended kiln conditions. The damage may range from a few slightly checked boards to loss of a significant volume of the kiln charge.

Some commercial operations have found from sad experience that certain species of oak timber growing in certain regions are likely to yield boards highly susceptible to serious honeycomb. Consequently, there can be a devaluation of top-grade logs by as much as $40 to $60 per 1,000 board feet.

Problems associated with the drying of oak 1See References at the end of the Paper.

have been discussed effectively by several work­ers including: Loughborough (1933), Kollmann (1950), Torgeson (1951, 1957), and Devine (1955). Pertinent to the problem of the extreme suscep­tibility of some oak boards to honeycomb and ring failure are the results of preliminary investiga­tions at the U.S. Forest Products Laboratory and the University of Wisconsin on the causes of shake in living trees,

It has been noted that green wood from oaks with shake. tended to emit a rancid odor and to surface check and honeycomb badly when dried. Ring failure also occurred and usually, but not always, was an extension of ring shake in the tree. Since a consistent association between bacteria-infected heartwood and shake has been found for both conifers and hardwoods (Ward et al. 1969, 1970), it was hypothesized that bac­terial stem infections may also explain the ex­treme difficulty of drying certain boards of oak.

The central hypothesis is that certain bacteria which can live in the heartwood of living trees will produce enzymes capable of degrading the com­pound middle lamella2 of wood cells during the

2The compound middle lamella is a combination of the intercellular substance called the true middle lamella and the adjoining primary cell walls.

early stages of infection. Thus. in the standing tree this middle-lamellar weakening predisposes the wood to shake formation from growth stresses, bending action of the wind, or freezing of capil­lary water within the degraded compound middle lamella. In the green board, this bacterially weakened wood will tend to check, honeycomb, or fail at the annual ring from drying stresses under normally mild drying conditions.

As a step in evaluating the hypothesis as well as in developing a practical method for detection

of honeycomb-susceptible oak lumber, it was de­cided to test the relationship of shake in the tree and abnormal, rancid, and sour vinegar odors in the wood to drying honeycomb and ring separa­tion Both ring and star shake in oak are easily observed on the end-grain surface. Rancid and sour odors in oak are usually detected as ac­curately by the human nose as by the gas chromat­ograph. In fact, within the same stem cross sec­tion, areas of infected and non-infected heartwood can often be differentiated by smell alone.

PROCEDURE

Six northern red oak (Quercus rubra L.) trees were selected from a second-growth forest in Richland County, Wis., during a commercial log­ging operation The sample trees were growing in mixture with white oak, sugar maple, red maple, red or slippery elm, basswood, and white ash on what is considered a good site for Wiscon­sin red oak according to Arend and Scholz (1969). The stand is located in a sheltered cove (fig. 1) and trees Nos. 1, 2, 3, and 5 containing rancid heartwood with shake were growing at the base of the slopes. Control trees Nos. 4 and 6, without shake, were located higher up on the slopes.

All sample trees were cut at a 1-foot stump. The stem of trees 1 to 5 were bucked into 8.6­foot logs up to a height where the potential log grade was estimated to be 3 or lower. Potential lag grade was estimated only on the basis of ex­ternal surface characteristics of the stem accord­ing to the specifications of Vaughan et al. (1966). Thus, if there had been no shake or butt rot all logs would have graded as either 1 or 2. The lower stem of tree 6 was inadvertently bucked into a 13-foot veneer log. At the termination of the log­ging operation, which was a light selection cut, tree 6 was found to be the only one cut from this area with the desired quality of heartwood. To ob­tain representative controls for the drying investi­gation, this log from tree 6 was included in the sample. The characteristics of the six red oak trees and logs used in the sample are presented in table I, and their patterns of occurrence in the stem are illustrated in figure 2,

The 15 logs were sawed into 1-1/8-inch-thick boards. All boards from every log were tallied on the green chain by a professional grader ac­cording to the standard grades of the National

Figure 1.--Second-growth hardwood stand in Richland County, Wis., at the time the sample red oak trees were cut. Sample tree 6 is shown in left foreground.

Hardwood Lumber Association (1967). For this study there were five lumber grade categories ranging from the top grades of Firsts and Seconds (PAS) and Selects to the grades No. 1 Common, No, 2 Common, and No. 3 Common, which is an allowed combination of No. 3A Common and No. 3B Common. No board from the 15 logs was below No. 3 Common grade.

FPL 165 2

Table 1.--Tree and log characteristics o f t h e six nor thern red oak sample trees

3

Figure 2.--Schematic trunk sections showing genera I patterns o f the heartwood char­acteristics described in Table 1 for six northern red oak trees. The stern cross-section disks iIlustrated in f igures 3 to 8 were taken at from 6 inches to 1.0 foot above the groundline.

(M 139 634)

Over 50 percent of the lumber yield from the 13­foot log of tree 6 graded as FAS, but for purposes of sample disbribution all boards from this log were cut into 6.5-foot-long boards. The respective boards were then designated as being from either theoretical logs A or B. This lowered the grade of all FAS boards to Selects because the minimum allowable board size for FAS is 6 inches wide by 8 feet long. Nevertheless, if judged on the basis of clear cutting size and board volume, 15 of the 6.5-foot boards might have still satisfied the other FAS grade requirements. These boards were not so designated in the results, but they did comprise 76 board feet or 35 percent of the total log volume,

The total volume yield of 1-1/8-inch-thick green lumber from all logs was 993 board feet. As shown in table 2, only 969 board feet were dried as

graded lumber since 24 board feet were required for 12 kiln samples.

When present, the greatest volume of shake and associated rancid heartwood was in the lower stem and tapered to a minimum in the pith of the upper logs. Disks taken from the stump of all six sample trees are shown in figures 3 to 8. There was a combination of shake types in the four test trees, but ring shake predominated in trees 1 and 5 (figs. 3 and 6), while spider heart or star shake predominated in trees 2 and 3 (figs. 4 and 5).

Although tree 4 contained an active nest of black carpenter ants (Camponotus pennsylvanicus) in the butt end of the first log, it was picked as a control tree because most of the stern was clear with sound, apparently normal heartwood, Sur­rounding the ant galleries was a zone of dark,

FPL 165 4

Table 2.--Yield and condition of heartwood of 1-1/8-inch green rough lumber from six northern red oak trees

stained heartwood with some incipient decay. As outlined In figure 7, the inner heartwood adjacent to the ant nest emitted a strong vinegar or acetic acid odor. Tree 4 also had a small core of ran­cid wood around the pith that extended from the groundline to the middle of log A.

Tree 6 was of excellent quality, and the heart­wood emitted a characteristic red oak odor ex­cept for a small pocket of rancid heartwood which surrounded the stained wood shown in figure 8 and extended for about 4 feet upwards.

5

Figure 3.--Stem section, 1 foot above ground, from northern red oak test tree I. The shake (Sk) and rancid heartwood are restricted largely to the inner core of the stem and the shake extends to about 10 feet above ground. The sapwood stain in the upper right is t h e result of injury by a stem-boring insect, followed by bacterial and fungal infections.

(M 136 415)

FPL 165 6

Figure 4.--Stem section, 1 foot above ground, from northern red oak test tree 2. Shake (Sk) and rancid heartwood extend almost to the sapwood in the lower 3 feet of the stem, and the shake tapers to a minimum in the pith zone at about 25 feet above ground. Over­grown carpenter worm exit holes are marked by CW.

(M 136 405)

7

Figure 5.--Stem sect ion, 1 foot above ground, from northern red oak test t r e e 3. Shake (Sk) tapers abruptly t o the pith in the lower 4 feet of the stem and ends at IT feet above ground. Rancid heartwood extends almost t o the sapwood and is found in the outer heartwood of both logs A and B.

(M 136 410)

FPL 165 8

Figure 6.--Stem section, 1 foot above ground, from northern red oak test tree 5. Shake (Sk) extends t o the middle heartwood and tapers to the pith at about 10 feet above ground. Rancid wood permeates almost the entire heartwood of log A and tapers slightly to the middle heartwood of logs B and C. Outwardly this tree was considered a crop tree, but extensive insect borer damage (arrows) existed in the pith and middle heart­wood of all logs.

(M 136 407)

9

Figure 7.--Stem section, 1 foot above ground, from northern red oak control tree 4. About one-fourth of the lower 4-foot stem section contains dark stains and incipient decay associated with an active carpenter ant nest (CA). Most of the tree contains clear, sound, normal-smelling heartwood, except for a central heartwood adjacent to the ant nest, which emitted a strong vinegar or acetic acid odor. The pith in the lower half of log A emitted a rancid odor.

(M 136 411)

FPL 165 10

Figure 8.--Stem section, 1 foot above ground, from northern red oak control tree 6. Most of t h e heartwood was clear, sound, and emitted a normal odor. A small pocket of ran­c i d wood extending to about 8 feet above ground surrounds the stained zone which is caused by an old red oak borer wound. The heart check (HCk) was caused by stem growth stresses after the tree was felled and is not considered shake.

(M 136 422)

11

Detection of the presence and types of micro­organisms in the six sample trees was made by culturing wood chips taken aseptically from stem sections sawed at 6 to 12 inches above the ground and in the upper stem above the top sam­ple log. Each stem section was split, the surface flame-sterilized, and then wood chips were ex­cised with a sterile chisel from points at the sap­wood, outer heartwood, middle heartwood, inner heartwood, and zones adjacent to shake separa-Mons. These chips were cultured in petri dishes on the solid agar (1.5 percent) surface of a malt extract: medium, a beef-extract-peptone medium, and an acid-hydrolyzed casein-yeast extract­starch-dextrose medium Also from each isolation point, chips were submerged in two tubes of semi­solid agar (0.2 percent) media to test for the presence of microaerophilic and strictly anaero­bic bacteria, One tube contained the acid-hydrolyzed casein-yeast extract-starch-dextrose medium, while the other tube contained the same formulation but reduced by adding L-cystine, sodium sulfide, and methylene blue indicator.

Evidence of damage by stem-boring insects was noted in the green boards from the sample trees, but the carpenter ants in the rot zone of tree 4 were the only living specimens collected. All six trees contained overgrown carpenter worm (Pri­onoxystus robiniae) holes, 1/2 inch or more in diameter, with associated stain, but not always rancid odors. The greatest number of carpenter worm holes were found in trees 2 and 5. Some of the trees, especially number 5, contained borer holes 1/4 to 1/2 inch in diameter which may be evidence of attack by the red-oak borer, Enapha­lodes rufulus. 3 In the butt log of tree No. 2 a cluster of small borer galleries, about 1/8 inch in diameter, appear to have been caused by the oak timber worm, Arrhenodes minuta. Tree No. 2 sustained the greatest damage from stem borers while the least damage was observed in control tree No. 6. MacAloney and Ewan (1964) have described these four stem-boring insects and their damage to hardwood trees of this region.

Six boards, Selects or better, were taken from the yields of trees 1, 3, 4, 5, and 6 and cut into twelve 32-inch-long kiln samples (table 3). The rest of the boards were then sorted and separ­ated into two dry-kiln charges. Charge 1, dried by a mild schedule, contained 487 board feet while charge 2, dried by an accelerated schedule, con­

tained 482 board feet. Each kiln charge contained a representative number of boards for each grade, log, and tree, and these representative pieces were evenly distributed throughout the loads.

Table 3.--Characteristics of the six boards noted in table 2, and of the twelve 32-inch-longkiln samples taken from these boards

Drying of both charges was started at the same time. The drying conditions shown in table 4 were based partly on recommended schedules for 4/4-inch northern red oak (U.S. Forest Products Laboratory 1937, and McMillen 1969). Tempera­ture and humidity changes were made when the wettest half of the six samples reached certain levels of moisture content.

After kiln drying, honeycomb and ring failure were detected by cutting small cross sections from clear wood portions of each board. Boards containing these internal defects were cut into shorter lengths to estimate their extent. The presence of honeycomb or ring failure was con­sidered a defect only if it occurred in a usable clear cutting, and the degrade was expressed as a loss in 1/4, 1/2, 3/4, or the total volume of the board as based on the original green dimensions. Losses due to shrinkage and warp were not meas­ured in this study.

3Until recently the red-oak borer was called Romaleum rufulum.

FPL 165 12

Table 4.--Drying conditions used for kiln-drying 1-1/8-inch-thick northern red oak boards

RESULTS

Figure 9 shows that under the mild drying con- outer heartwood adjacent to the rot. Clear, ditions the green lumber was dried from 86 to 7 normal-smelling heartwood did not develop either percent average moisture content in 20 days. honeycomb or ring failure. However, a significant Under the accelerated drying conditions the amount of rancid heartwood dried without internal charge was dried from 87 to 7 percent average checking, especially under the mild schedule. moisture content in 16 days. Dark-stained heartwood did not always check even

Honeycomb occurred in varying amounts in under the more severe drying conditions. lumber from all six trees and, except for boards The loss of volume due to the presence of honey-with pith. it was always in heartwood that emitted comb and ring failure is shown in table 5. There abnormal odors. Ring failure occurred only in was a greater loss in lumber volume from the rancid-smelling boards and only from the four trees with shake, and within this group the loss trees with shake. Of the vinegar-smelling boards was increased by accelerating the drying condi­from tree No. 4, honeycomb developed only tions. in those boards containing pith and not in the

13

Figure 9.--Kiln conditions and drying curves for 1-1/8-inch-thick northern red oak lumber with both normal and rancid heartwood.

(M 139 631)

All rancid and vinegar-smelling heartwood isolated from the inner heartwood zones or from consistently yielded a mixture of two apparently wood adjacent to shake separations. The other, different strains of anaerobic bacteria. Both more common, anaerobe was a short rod-shaped anaerobes were motile, gram-positive, rod- bacterium, about 0.5 by 1.0-1.3 µ m, that often shaped organisms. A long, narrow rod-shaped formed chains in culture. Clostridium with a terminal spore was usually

FPL 165 14

Table 5.-- Loss of board volume (green basis) in 1-1/8-inch-thick northern red oak from either honeycomb or ring failure after kiIn drying

Aerobic bacteria similar to Bacillus cereus arations. were frequently isolated from old shake zones in The darkly stained wood around the carpenter the central core of the stem or, in association ant galleries in tree 4 yielded an unknown non­with the mold Paecilomyces varioti, from stained hymenomycetous fungus which seems to produce wood around insect borer holes. Sometimes yeasts only dark aleurospores in culture. were isolated from old darkly stained shake sep­

15

DISCUSSION

Significance of Rancid Heartwood and Bacterial Infections

The emission of offensive rancid or sour vine­gar odors is a salient feature of red and black oak heartwood in trees with shake and of most green oak boards which tend to honeycomb. These odors are due to a mixture of volatile fatty acids re­sulting from infection by anaerobic bacteria Anal­ysis by gas chromatography of infected wood showed such acids as butyric, valeric, and caproic, as well as elevated amounts of propionic and acetic acids. Normal heartwood contained only small amounts of acetic acid and possibly traces of propionic acid (Zinkel, et al. 1969).

As indicated in table 5, the greatest losses from honeycomb and ring failure were in shake trees 2, 3, and 5, and these are the trees with the most ex­tensive rancid heartwood. However, tree No. 2 did not have any more extensive rancid heartwood than trees 3 and 5, yet the volume loss was twice as much as either tree 3 or 5; this additional loss was in the form of honeycomb. Additional research information is needed before the unusually high losses from tree No. 2 can be adequately explained. Perhaps tree No. 2 was infected longer and thus the wood was weaker. The possibility exists, though, that differences in bacterial strains may explain why tree No. 2 was more susceptible to honeycomb.

Ring Failure and Honey­comb Differences

Ring failure occurred only in rancid heartwood from the four trees with shake and in all grades of lumber from these trees. The magnitude of ring failure was greater in boards from the butt logs than in boards from the upper B and C logs. Ring failure occurred either as a longitudinal extension of existing ring shake or, as shown in figure 10, in sound green boards from the outer heartwood of logs with shake centers.

4 Ward, Kuntz, and McCoy (1970) proposed that shake by bacteria is then subjected to either one or a pressures from bacteria growth, or, probably most growth stresses described by Jacobs (1945), Boyd

This suggests the possibility that ring failure is an incipient form of ring shake which is first ini­tiated by stresses4 in the standing tree. However, the actual visible rupture in ring failure is prob­ably precipitated by drying stresses similar to those indicated in figures 11 and 12. Honeycomb, on the other hand, is more likely to be initiated by drying stresses, since most pieces of green oak may honeycomb with excessive drying tem­peratures, whereas relatively few pieces develop ring failure.

Rasmussen (1961) suggests that both honeycomb and ring failure can be kept to a minimum by using higher initial relative humidities and lower dry-bulb temperatures, but he adds that end-coating the stock is also necessary for reducing ring failure. Possibly the end-coating prevents the ex­tension of ring shake already present. In this study the boards were not end-coated and there seemed to be little difference in the amount of ring failure occurring under the two drying con­ditions. Examples of ring failure in boards dried under both kiln schedules are shown in figure 13. The additional loss in board volume from drying under the accelerated schedule is attributed to honeycomb.

Drying Conditions

In this study, the effect of drying conditions was manifested largely in formation of honeycomb rather than ring failure. Since honeycomb oc­curred only in rancid heartwood under both mild and accelerated drying, it is evident that very mild drying conditions must be employed to minimize honeycomb when the charge contains rancid red oak. By the same token, normal 4/4 xed oak lum­ber can probably be kiln dried much faster than under the accelerated conditions of this study if it is segregated from rancid wood. Additional re­search must be done on oak heartwood emitting a vinegar smell because only these boards con­taining pith checked internally.

forms in the tree stem when heartwood first weakened combination of the following stresses: Freezing, gas important, bending action of the wind and the stem

(1950), and Kubler (1959, a, b).

FPL 165 16

Excessive dry-bulb temperatures , especially during the middle stages of drying green oak, seem to be a key factor contributing to honeycomb for­mation. When drying rancid oak, highinitial rela­tive humidity conditions which minimize surface checks must also be maintained because this wood is susceptible to bottleneck checking. Bottleneck checking is a form of honeycomb that starts from deep surface checks during the initial stages of drying (fig. 14). Kollmann’s (1950) data from the drying of a European white oak species, Quercus pedunculata, indicates that surface checks can occur at temperatures as low as 104° F. if the relative humidity is low. He found that the initia­tion of internal checking is not necessarily as­sociated with a specific temperature; Once inter­nal checking starts, however, the magnitude of internal checking or honeycomb increases with an increase in temperature.

Because bacterial infections appear to cause rancid heartwood in red oak. the combined ef­fect of time and temperature and its relationship to stock thickness is extremely important in the kiln drying of rancid wood. The presence of shake in the tree indicates that the green heartwood has already been weakened by (a) bacterial enzymes acting directly on the wood cells, (b) hydrolysis by volatile fatty acids produced from the carbo­hydrate metabolism of the bacteria, or (c) a combination of both factors. Shrinkage stresses and strains and additional acid hydrolysis under normally safe drying conditions may then be sufficient to cause rupture and honeycomb. On the basis of experience with commercial kiln opera­tions, it is likely that more or all of the rancid oak in this study would have honeycombed if the boards had been 6/4 inch or thicker. This is probably because the wet core of thicker stock is held under elevated temperatures for a longer time, thus causing additional weakening of the wood.

Significance of Lumber Grades

There is a dearth of data on the kiln drying of green oak lumber in the lower grades-andf for good reason. It takes at least three times as long to kiln dry 4/4 oak from a green condition as from an air-dried condition (Rasmussen 1961).

Production economics necessitates that kiln space be utilized as fully as possible with a mini­mum of lumber defects or nonusable wood. Kiln space is best utilized with charges of No. 1 Com­mon and Better lumber, but air-dried lumber in the lower grades such as No. 3A Common oak for flooring is often kiln dried. Our main reason for kiln drying the green lumber in the lower grades was to compare the possible contribution of lum­ber defects to honeycomb and ring failure with the presumed contribution of rancid heartwood. We were also interested in the occurrence of honey­comb and ring failure with respect to total volume yield from each log,

Oak boards are graded on the basis of usable content, which is essentially the volume of clear and sound wood that will yield cuttings of mini­mum sizes. The top grades of PAS must have a minimum cutting of sound wood, clear on bath sur­faces, that measures either 4 inches wide by 5 feet long, or 3 inches wide by 7 feet long. No. 3 Common, the lowest grade, must yield minimum cuttings of sound wood, clear on one surface, that measures 3 inches wide by 2 feet long or of sound wood 1-1/2 inches by 2 feet. In this study, defects which reduced the grade of green oak boards were: (1) Sound knots; (2) holes or voids from unsound or loose knots, galleries of car­penter worm and other grubs, bark pockets, and decay; (3) splits from shake; (4) pith; and (5) streaks and spots of dark discolorations often referred to as mineral stains.

The bar graphs in figure 15 compare the total loss in green volume from honeycomb and ring failure when all grades are dried with the losses when only No. 2 Common and Better and when only No. 1. Common and Better are dried. The loss in volume from degrade decreases with increase in lumber grade. In the upper grades, the presence of honeycomb and ring failure is still quite signi­ficant in lumber from the trees with shake. For the control trees 4 and 6, there was no loss in the No. 1 Common and Better lumber and little or no loss in No. 2 Common and Better. When it is necessary to kiln-dry green oak boards with a rancid odor, evidently a marked reduction in honeycomb and possibly ring failure can be real­ized if the better grades are dried under mild schedule s

17

Figu

re

10.--R

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fail

ure

(R

F)

and

shak

e (S

k)

in

sect

ions

fro

m

boar

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saw

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the

sam

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A

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red

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Bot

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w

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dr

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unde

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ter

hear

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(M

138

332)

(M

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Figu

re

11.--R

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failu

re

(RF)

an

d ho

neyc

omb

(HC

b)

in

a se

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a

Sel

ect

grad

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ard

(No.

13

3)

from

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Th

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ngly

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. Th

e bo

ard

was

ki

ln

drie

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der

the

acce

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ted

sche

dule

, an

d it

appe

ars

that

sh

rinka

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and

cupp

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toge

ther

w

ith

inci

pien

t rin

g sh

ake

caus

ed

the

ring

failu

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durin

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. Th

e co

mbi

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ra

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cu

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and

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failu

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is

also

se

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in

figur

e 12

.

(M

138

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Figu

re

12.--B

oard

se

ctio

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m

log

A

of

tree

5 sh

owin

g rin

g fa

ilure

w

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ei

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da

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(DD

) or

di

d no

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(D

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durin

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ln

dryi

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unde

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ild

sche

dule

. Th

e gr

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boar

d w

as

ranc

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clea

r an

d gr

aded

FA

S.

(M

138

809)

Figu

re

13.--E

xam

ples

of

rin

g fa

ilure

(R

F)

and

hone

ycom

b (H

Cb)

in

se

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ns

from

tw

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A

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unde

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kiln

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ons.

(M

13

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(M

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Figu

re

14.--S

ectio

ns

from

an

FA

S

north

ern

red

oak

boar

d w

ith

ranc

id

hear

twoo

d w

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dark

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durin

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S

ome

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b ch

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ar

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varie

ty

(arr

ows)

.

(M

133

440)

Figure 15.--Effect of drying conditions on occurrence of ring failure and honeycomb in 1-1/8-inch-thick green northern red oak when different grades are dried.

(M 139 633)

Pith

Some internal checking occurred in most boards containing pith, Rancid odors apparently begin in the pith zone of most red oaks, but we cannot be certain about the cause of honeycomb in rancid boards containing pith because Rasmussen (1961) notes that it is almost impossible to dry any board containing pith without some defect. The diffi­culties when seasoning hardwood boards contain­ing pith are attributed partly to growth stresses that developed in the living tree and partly to seasoning stresses. Extensive studies on tree growth stresses and their effects in cut timber have been reported by Jacobs (1945), Boyd (1950), and Kubler (1959 a, b, c). Of the total lumber yield for this study, only boards grading No. 2 Common and lower contained pith. Therefore, the losses from honeycomb or ring failure shown in figure 15 far No, 1 Common and Better grades are primarily associated with rancid heartwood. Figure 16 shows

internal checking in a normal heartwood board with pith. Oak boards, rancid or normal, which have pith also contain more knots, overgrown bark, and other defects than do boards from the outer heart­wood.

Dark Stains and Associated Defects

It is not unusual for deep surface checks and even honeycomb to develop in the stained wood of oaks. McMillen (1969) found when kiln drying green, presurfaced, normal-smelling northern red oak boards that dark stains associated with in­sect injuries surface checked, while iron tannate stains from the wet surfacing operation did not. Even under relatively mild air-drying conditions honeycomb developed in 4/4-inch boards of nor­thern red oak (Sachs, et al. 1966) and of water

23

5oak, Quercus nigra, which contained dark stains, but these boards also emitted rancid odors. Although oak heartwood with dark stains will often emit rancid odors. it appears that these two characteristics are probably independent of each other with respect to causes (Bulgrin and Ward 1968),

Figure 16.--Badly checked No. 3 Comon board from the upper log B of control tree 6 that was kiln dried under mi Id conditions. The heartwood had a normal oak odor and the checks may be due to a combination of seasoning stresses and residua I tree growth stresses associated with the pith.

(M 138 397)

In this study we were concerned with the possi­ble extension of honeycomb or ring failure from stained to clear zones of wood, Dark stains occur­ring in the present sample of boards were mostly associated with carpenter worm (Prionoxystus robiniae) holes, but also with some old shake separations, pith, and fungal action.

Although stained oak heartwood has a tendency to surface check, the board sections shown In figure 17 indicate that insect borer holes and as­sociated stain do not always cause honeycomb or ring failure. Nevertheless, a direct associa­tion of honeycomb with insect borer galleries, as shown in figure 18, was found in many rancid boards, especially those from butt logs.

It seems that rancid bacterial heartwood is more likely to occur around overgrown insect

holes in the lower trunk of the tree than around insect holes higher up in the stem. Numerous field observations on red oak trees suggest to us that there may be a cause and effect relationship between the establishment of rancid heartwood bacteria and the occurrence of insect wounds and borer holes in the roots, root collar, and butt section of the trunk.

As shown in figure 19, stains associated with heartwood decay by fungi will not always surface check or honeycomb during kiln drying.

From all specimens examined to date, red oak boards containing shake from the tree invariably have rancid heartwood. Shake in red oak boards may or may not have dark discolorations associ­ated with it, and this inconsistency appears to be carried over into the drying process where ran­cid heartwood may or may not darken during dry­ing. Usually, but not always, the inner core of ran­cid oak boards with honeycomb will also have darkened considerably during kiln drying as shown in figure 14. On the other hand rancid oak boards

that have seasoning-darkened cores may some­times be free of honeycomb. As shown in figure 12, somewhat the same situation holds for ring failure which may or may not darken during kiln drying.

Tight Knots

Because only logs from the lower stem were used, there were relatively few tight knots and none were derived directly from live branches. All tight knots checked and, as shown in figure 20, there was sometimes limited extension of the checks into adjacent clear cuttings with severe rancid heartwood. It was not possible, though, to determine from the present sample if tight knot checks would extend more into rancid rather than normal heartwood cuttings.

Bark Pocket and Associated Defects

Bark is usually occluded within the stem xylem when knots, insect borer holes, and other wounds are overgrown by callus tissue. The microflora of oak bark is quite rich in species of bacteria,

5 Darwin, W. N., Jr. 1968. Personal Communication, Jan. 16. US FPL File No. 4110. TMR Programs, USFS, Southern Forest Exp. Sta., Stoneville, Miss.

FPL 165 24

Figu

re

17.-

-Sec

tions

fro

m

a N

o.

1 C

omm

on

boar

d fro

m

log

A

of

red

oak

tree

2.

Alth

ough

ki

ln

drie

d un

der

the

ac

cele

rate

d S

ched

ule,

rin

g fa

ilure

(R

F)

and

hone

ycom

b (H

Cb)

fo

rmed

in

th

e cl

ear,

ranc

id

hear

twoo

d of

th

e m

id

and

tow

er

sect

ions

, bu

t no

t in

th

e

top

sec­

tion

with

a

carp

ente

r w

orm

ho

le

(CW

) an

d as

soci

ated

st

ain.

(M

138

323)

Figu

re

18.--C

arpe

nter

wor

m

(CW

) an

d oa

k tim

berw

orm

(O

T)

hole

s in

se

ctio

ns

from

a

No.

3

Com

mon

bo

ard

from

th

e bu

tt lo

g A

of

re

d oa

k tre

e 2.

Th

e bo

ard

had

ranc

id

hear

twoo

d.

The

hone

ycom

b (H

Cb)

th

at

seem

s to

be

di

rect

ly

asso

ciat

ed

with

th

e bo

rer

hole

s w

as

form

ed

durin

g dr

ying

un

der

mi

Id

kiln

co

nditi

ons.

(M

138

713)

Figu

re

19.--K

iln

drie

d bo

ard

sect

ion

from

lo

g A

of

tre

e 4.

W

hen

gree

n th

e bo

ard

grad

ed

as

a S

elec

t an

d th

e w

ood

was

so

und,

bu

t th

e da

rk

stai

ns

(arr

ows)

w

ere

asso

ciat

ed

with

th

e ca

rpen

ter

ant

nest

sh

own

in

figur

e 7.

A

lthou

gh

drie

d un

der

the

acce

lera

ted

sche

d­ul

e ne

ither

th

e cl

ear

woo

d no

r th

e st

aine

d w

ood

cont

aine

d ho

neyc

omb.

(M

138

803)

Figure 20.--Sections from a No. 1 Common board (No. 94) from log B of tree 2 showing a badly checked sound or tight knot (SdK). The board was dried under mild kiln condi­tions, but there is limited extension of honeycomb (HCb) into the clear cuttings which contained rancid heartwood.

(M 138 370)

yeasts, and fungi, so bark pockets are a likely infection court for bacteria which can came ran­cid heartwood. All of the six red oak trees in this study had a number of overgrown insect borer holes and unsound knots with the bark pockets. After examining all green boards prior to season­ing, It did not appear that these defects could always be sources of infection by rancid wood bacteria, because they were often embedded within normal-smelling heartwood.

When rancid heartwood was present, the com­bination of bark pocket with insect wounds or with unsound knots seems to contribute to honeycomb and deep surface checking under accelerated kiln drying conditions. From the results of this study, it appears that bark pockets and associated defects in clear, normal-smelling heartwood will not cause degrade in the adjacent clear cuttings when dried under normal kiln conditions. An example is shown in figure 21.

FPL 165 28

Figure 21.--Board section from log C of red oak tree I which was dried under mild kiln conditions. The bark pocket (BP) and overgrown, unsound knot (UnK) are imbedded in clear, normal heartwood which did not check o r honeycomb during drying.

(M 138 335)

Position of Logs in the Stem and Oak Lumber Degrade

Naturally the most valuable yields of lumber or veneer are obtained from the butt logs of sound, vigorous, red oak trees with a lower stem free of branches, bumps, and bark distortions. As pre­

viously mentioned, our field observations suggest that the bacteria responsible for rancid heartwood are quite likely to become established in the tree from injuries to the roots and root collar. Stern and root-boring insects commonly cause these injuries. but wet, poorly drained soils may con­tribute to direct bacterial invasion from the soil to the roots.

29

Thus it is not unusual on certain sites for vigorous, apparently high quality red oaks to have rancid heartwood in the valuable butt log. With time, rancid heartwood is invariably followed by shake and a consequent loss in volume of higher grade lumber and veneer.

The results of this study indicate that even when shake has not started in the rancid heartwood, there is still. the likelihood that the wood will be lost during drying. The bar graphs in figure 22 shew that the greatest loss from either honeycomb or ring failure occurs in the butt logs of trees with

rancid heartwood and shake. To a much lesser ex­tent, these losses also occurred in the control trees without. shake and with generally normal heartwood (figs. 23 and 24). However, when only No. 1 Common and Better boards are dried, there were still significant losses in lumber from the shake trees, but no losses in lumber from the con­trol trees. Figure 22 shows the losses to be great­er in No. 1 Common and Better lumber from the butt log of the shake trees, but these losses can be greatly minimized (27 pct. in this study) by dry­ing under milder drying conditions.

Figure 22.--Lumber yield and seasoning losses in 1-1/8-inch-thick green boards as re­lated to position in the stem of 8.6-foot-long logs from four northern red oak trees containing shake and rancid heartwood. Butt or A logs begin at I foot above ground and top or C logs end at 26.8 feet.

(M 139 635)

FPL 165 30

Examination of the lumber defects in this study lished in and spread from focal points in the indicates that injuries and defects associated with lower stem or root collar. Excessively moist soil stem-boring insects warrant additional attention conditions also seem to be associated with red oak in future studies on the causes of rancid heart- trees that have a high incidence of rancid heart­wood in oak trees. Although insect holes, alone wood but this does not always have an adverse and in combination with unsound hots and bark effect on the growth and vigor of the tree. pockets, were found in normal-smelling heart- Morris (1964) found that insect bores injuries wood, it appears that insect injuries contribute caused a loss in northern red oak lumber value of to rancid heartwood when they occur in the lower $10.27 per thousand board feet at a flooring mill stem or root collar. No matter where insect in- and of $27 per thousand at a furniture plant. It juries occur in the tree, they will provide an en- appears that these insects may well contribute to trance for the invasion of bacteria. However, it additional losses if they also are responsible for seems that the particular strains of bacteria the establishment and spread of bacteria causing which cause rancid heartwood are usually estab- rancid heartwood

Figure 23.--Lumber yield and seasoning losses in 1-1/8-inch-thick green boards as re­lated to position in the stem of 8.6-foot-long logs from northern red oak control tree 4. Log A begins at I foot above ground and log C ends at 26.8 feet.

(M 139 632)

31

Figure 24.--Lumber yield and seasoning losses in 1-1/8-inch-thick green boards as re­lated to position in the stem of 6.5-foot-long logs from northern red oak control tree 6. Log A begins at 1 foot above ground and log B ends at 14.0 feet.

(M 739 630)

FPL 165 32

IN SUMMARY

Red oak heartwood from trees infected with cause of associated shake and bacterial infection certain species of bacteria will emit a “sour” or patterns in the tree, rancid heartwood tends to be “rancid” odor which is a mixture of volatile fatty more prevalent in the lower stem section of xed acids that commonly includes propionic, butyric, oaks and the lumber from the butt log will con­valeric, and caproic as well as elevated amounts tain more rancid heartwood than the upper logs. of acetic acid The “rancid” heartwood is weaker In red oak. rancid heartwood may form after than sound red oak heartwood with normal odors the tree is infected by certain strains of bac­and is very susceptible to honeycomb formation teria that have entered through injuries in the under normal kiln-drying conditions. Severity of stem or roots. Among the injuries that may pro-honeycomb in rancid heartwood increases when vide infection courts, those caused by insect the drying rate of the wood is accelerated. The borers in the lower stem or root collar are most accelerated kiln schedule used in this study did noteworthy. Site and tree growth conditions may not cause honeycomb in clear, normal-smelling promote the extension of rancid heartwood with-oak Ring failure also occurs in rancid heartwood, in the stem. but it appears to be an incipient form of ring shake This study indicates that the kiln drying of rough that was initiated in the tree and then ruptured green 4/4-inch northern red oak lumber may be from kiln-drying stresses. There seemed to be greatly a c c e l e r a t e d without causing honey-little difference in the amount of ring failure in comb if the charge does not contain boards with boards dried under accelerated conditions when rancid heartwood. Boards with rancid heartwood compared with boards dried under mild conditions. can be dried with a minimum loss from honey-

Under kiln drying conditions. honeycomb and comb if only the upper grades, especially No. 1 ring failure can occur in all grades of green red Common and Better, are subjected to mild kiln oak lumber with rancid heartwood. However. be- conditions.

33

REFERENCES

Arend, J. F., and Scholz, H. F. 1969. Oak forests of the Lakes States and

their management. USDA, Forest Ser­vice Res. Pap. NC-31, North Central Forest Exp. Sta., St. Paul, Minn.

Boyd, J. D. 1950. Tree growth stress. II. The develop­

ment of shakes and other visual fail­ures in timber. Austral. J. of Appl. Sci. 1: 296-312.

Bulgrin, E. H., and Ward, J. C. 1968. Factors contributing to h e a r t w o o d

boundary stain in living oak. Wood Sci. 1(1): 58-64.

Devine, J. 1955. Drying oak green from the saw. Nat.

Hardwood Mag. 28(2): 31-32.

Jacobs, M. R. 1945. The growth stresses of woody stems.

Commonwealth Forest. Bur. Bull. No. 28, 67 pp. Canberra, Australia.

Kollmann, F. 1950. Causes of defects in drying: green oak

and strength tests on wood in the high-frequency alternating field. Swedish Wood Res. Inst. Tech. Dep. Bull. 21, Stockholm.

Kubler, H. 1959. Studies on growth stresses in trees.

(a) Part I. The origin of growth stresses and the stresses in trans­verse direction. Holz als Roh- und Werkstoff 17: 1-9. (b) Part II. Longi­tudinal stresses. Ibid.: 44-54. (c) Part III. Effect of heat treatment on the dimensions of green wood. Ibid.: 77-86.

Loughborough, W. K. 1933. Kiln drying green oak for beer barrels.

USDA, FS, Forest Prod. Lab. Rep. 1010, 5 pp.

MacAloney, H. J., and Ewan, H. G. 1964. Identification of hardwood insects by

type of tree injury, North Central Region USDA Foreat Serv. Res. Pap. LS-11, North Central Forest Exp. Sta., St. Paul, Minn.

McMillen, J. M. 1969. Accelerated kiln drying of presurfaced

1-inch northern red oak. USDA Forest Serv. Res. Pap. FPL 122, Foreat Prod. Lab.

Morris, R. C. 1964. Value losses in southern hardwood lum­

ber from degrade by insects. U.S. Forest Serv. Res. Pap. SO-8. So. Forest Exp. Sta., New Orleans, La.

National Hardwood Lumber Association 1967. Rules for the measurement and inspec­

tion of hardwood and cypress lumber. 116 pp, Chicago, Ill. 60605.

Rasmussen, E. F. 1961. Dry kiln operator’s manual. USDA Agr.

Handbook No. 188, 432 pp.

Sachs, I. B., Ward, J. C., and Bulgrin, E. H. 1966. Heartwood stain in red oak. Holz als

Roh- und Werkstoff 24: 489-497.

Torgeson, O. W. 1951. What precautions will minimize season­

ing defects in the kiln drying of green oak lumber? USDA, FS, Forest Prod. Lab. Rep, No. D1769-11, 2 pp.

1957. Schedules for the kiln drying of wood. USDA, FS, Forest Prod. Lab. Rep. NO. 1791 (Rev.), 16 pp.

U.S. Forest Products Laboratory 1937. Hardwood and softwood drying sched­

ules. Tech. Note. No. 175, 8 pp.

FPL 165 34

Vaughn, C. L., Wollin, A. C., McDonald, K. A., and Bulgrin, E. H. 1966. Hardwood log grades for standard lum­

ber. U.S. Forest Serv. Res. Pap. FPL 63, 52 pp. Forest Prod. Lab.

Ward, J. C., Kuntz, J. E., and McCoy, E. 1969. Bacteria associated with shake in broad

leaf trees. Phytopathol. 59: 1056.

, Kuntz, J. E., and McCoy, E. 1970. Another look at shake in trees. Pre­

sented at Joint Tech. Program of the Soc. of Wood Sci. and Technol. and Forest Prod. Res, Soc. Miami Beach, Fla. (June 29).

Zinkel, D. F., Ward, J. C., and Kukachka, B. F. 1969. Odor problems from some plywoods.

Forest Prod. J. 19: 60.

35

ACKNOWLEDGMENTS

The authors are indebted to the following friends and associates for their valuable assistance and advice in this study Owen Smith, owner and operator of Owen Smith Sawmill, Richland Center, Wis.; William Swarting, Consulting Forester, Richland Center, Wis.; Rudolf Nigl, Forester, Wisconsin Department of Natural Resources; Prof. Elizabeth McCoy, Department of Bacteri­ology, and Prof. Arthur Kelman, Department of Plant Pathology, University of Wisconsin; Harold F. Scholz, U.S. Forest Service (retired); and Coleman L. Vaughan, Donovan R. Every, and James R. Vargo of the U.S. Forest Products Laboratory.

FPL 165 36 3.5-37-4-72 U.S. GOVERNMENT PRINTING OFFICE: 1981–554-279

D 169 SE 22

U.S. Forest Products Laboratory.

Honeycomb and ring failure in bacterially infected red oak lumber after kiln drying, by J. C. Ward, R. A. Hann, R. C. Baltes, and E. H. Bulgrin. Madison, Wis., F.P.L. 1972.

37 p. (U.S.D.A. FS res. paper FPL 165)

Northern red oak lumber from t r ees with heartwood in­fected by anaerobic bacteria proved more susceptible to honeycomb and ring failure during kiln drying than s imi lar lumber f rom non-infected heartwood.