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Issued September 20, 1911. 

U. S. DEPARTMENT OF AGRICULTURE, 

FOREST SERVICE BULLETIN 75. 

HENRY S. GRAVES, Forester. 



CALIFORNIA TANBARK OAK. 



PART I. Tanbark Oak and the Tanning Industry. 

By WILLIS LINN JEPSON, Collaborator. 

t* 
PART II. Utilization of the Wood of Tanbark Oak. 

By H. S. BETTS, Engineer in Timber Testa, . ( 

APPENDIX. Distribution of Tannin in Tanbark Ok*. : ' 

By C. D. MELL, Assistant Dendrologist;' * / : 




SEC 




OCT 29 1914 

Division of Forestry 
University of California 



WASHINGTON: 

GOVERNMENT PRINTING OFFICE. 
1911. 




LETTER OF TRANSMITTAI, 



U. S. DEPARTMENT OF AGRICULTURE, 

FOREST SERVICE, 

'./ : I/: : : Washington, D. C., March 13, 1911. 

*SiR: 1 have., the honor to transmit herewith a manuscript entitled 
!?tCaJffiryia.'Ta2jbark Oak/' by Willis Linn Jepson, collaborator, and 
H. S. Betts, engineer in timber tests, together with an Appendix by 
C. D. Mell, assistant dendrologist, and to recommend its publication 
as Bulletin 75 of the Forest Service. This bulletin shows how the 
complete product of tanbark oak its bark and its wood may be 
utilized. It is important that this complete utilization should be 
brought about. The wood is now left in the forest to rot unused or 
to add fuel to forest fires. The timber tests show that the lumber 
has a high value and can be put to the same uses to which the eastern 
oaks are put. A careful handling of woodlands, coupled with con- 
servative lumbering, ought to make the tanbark-oak crop continuous 
and render this resource inexhaustible. 

Respectfully, . HENRY S. GRAVES, 

Forester, 
Hon. JAMES WILSON, 

Secretary of Agriculture, 
2 



CONTENTS. \ 



PART I. TANBARK OAK AND THE TANNING INDUSTRY. 

Page. 

Development of the tanning industry in California 5 

Silvical characteristics of the tanbark oak 6 

Range and occurrence 7 

Associates 8 

The production of tanbark 8 

Centers of the industry 8 

Stand and yield 9 

Peeling 10 

Transportation 12 

Quality of the bark 14 

Prolonging the supply 15 

Providing for second growth 16 

Sprout reproduction 16 

Reproduction by seed 17 

Second-growth bark 17 

Quality of second-growth bark 18 

Conservative methods in the woods 19 

Guarding against fire 19 

Tannin-extract processes 20 

Supplemental materials 21 

Possibilities of utilizing the wood 22 

Conclusions 23 

PART II. UTILIZATION OF THE WOOD OF TANBARK OAK. 

Tanbark oak lumber 24 

Appearance and characteristics of the wood 24 

Strength '. 25 

Seasoning 28 

Shrinkage 29 

Hardwoods used on the coast 30 

Suggested uses for tanbark oak 31 

APPENDIX. 

Distribution of tannin in tanbark oak 33 

3 



477598 




: 



LETTER OF TRANSMITTAL 



U. S. DEPARTMENT OF AGRICULTURE, 

FOREST SERVICE, 

\: /: * Washington, D. C., March 13, 1911. 

"SiR* 1 have.4he honor to transmit herewith a manuscript entitled 
t^*ta!ifC)riiia."Tai?bark Oak/' by Willis Linn Jepson, collaborator, and 
TEE S. Betts, engineer in timber tests, together with an Appendix by 
C. D. Mell, assistant dendrologist, and to recommend its publication 
as Bulletin 75 of the Forest Service. This bulletin shows how the 
complete product of tanbark oak its bark and its wood may be 
utilized. It is important that this complete utilization should be 
brought about. The wood is now left in the forest to rot unused or 
to add fuel to forest fires. The timber tests show that the lumber 
has a high value and can be put to the same uses to which the eastern 
oaks are put. A careful handling of woodlands, coupled with con- 
servative lumbering, ought to make the tanbark-oak crop continuous 
and render this resource inexhaustible. 

Respectfully, . HENRY S. GRAVES, 

Forester. 
Hon. JAMES WILSON, 

Secretary of Agriculture, 
2 



CONTENTS. \ 



PART I. TANBARK OAK AND THE TANNING INDUSTRY. 

Page. 

Development of the tanning industry in California 5 

Silvical characteristics of the tanbark oak 6 

Range and occurrence 7 

Associates 8 

The production of tanbark 8 

Centers of the industry 8 

Stand and yield 9 

Peeling 10 

Transportation 12 

Quality of the bark 14 

Prolonging the supply 15 

Providing for second growth 16 

Sprout reproduction 16 

Reproduction by seed 17 

Second-growth bark 17 

Quality of second-growth bark 18 

Conservative methods in the w r oods 19 

Guarding against fire 19 

Tannin-extract processes 20 

Supplemental materials 21 

Possibilities of utilizing the wood 22 

Conclusions 23 

PART II. UTILIZATION OF THE WOOD OF TANBARK OAK. 

Tanbark oak lumber 24 

Appearance ajid characteristics of the wood 24 

Strength '. 25 

Seasoning 28 

Shrinkage 29 

Hardwoods used on the coast 30 

Suggested uses for tanbark oak 31 

APPENDIX. 

Distribution of tannin in tanbark oak 33 

3 



477598 



ILLUSTRATIONS. 



PLATES. 

Page. 

PLATE I. What is left after the tanbark is removed Frontispiece. 

II. Typical tanbark oak country where, in the redwood belt, the tree 

attains its best development 8 

III. Fig. 1. Typical tanbark oak tree undergoing removal of first ring of 

bark. Fig. 2. Closer view of the operation 12 

IV. Fig. 1. Peeling 4-foot rings of bark from the felled tree. Fig. 2. 

Bunching the bark in small piles along the sled road 12 

V. Fig. 1. The skid ways to which the bunched bark is sledded, and 
from which it is hauled to the railroad. Fig. 2. Hauling the bark 

in wagons from the skidways to the cars 12 

VI. Fig. 1. Machine and method used for testing small beams. Fig. 2. 
Seasoning checks in the butt of a tanbark oak log exposed to the hot 

sun for six weeks 24 

VII. Fig. 1. Tanbark oak lumber for car construction. Fig. 2. Tan- 
bark oak boards air-drying 24 

VIII. Fig. 1. Tanbark oak flooring, and the method of storing and sorting it. 

Fig. 2. Tanbark oak flooring ready for shipment from the mill. . 28 
IX. Transverse section of a 2-year-old twig of tanbark oak, showing tannin 

in the pith, pith-rays, and bark 28 

X. Fig. 1. Transverse section of a 3-year-old twig of tanbark oak, show- 
ing the distribution of tannin in the pith and pith -rays. Fig. 2. 

Longitudinal radial section of a 3-year-old twig 28 

4 



uu 



OCT 29 1914 

Division of Forestry 
University of California 



CALIFORNIA TAN BARK OAK. 



a) 

PART I. TANBARK OAK AND THE TANNING INDUSTRY, 1 

By WILLIS LINN JEPSON. 
DEVELOPMENT OF THE TANNING INDUSTRY IN CALIFORNIA. 

Tanbark oak is, economically, the most important of the 15 Pacific 
coast oaks, because it furnishes the chief material used in the exten- 
sive tanning industry of that region. In 1900, according to the 
census, California ranked third among the States in the value of 
tanned hides produced. Commercial tanning on the Pacific coast 
began with the influx of Americans into California in 1849 and 1850. 
As early as 1852 Sonoma County had one tannery which produced 
$30,000 worth of leather, and by 1856 there were 18 in the State, in 
which $94,000 was invested. The bark of the tanbark oak was first 
used at Santa Cruz, and in 1857 a tannery there with an output of 
700 hides a month was the largest in the State. Its leather was 
superior to that produced by the establishments which still used the 
live-oak and black-oak bark, the first utilized. By 1859 there were 
29 tanneries and their product was more than sufficient for home 
consumption. In the next year the value of the output of the State's 
tanneries was $276,014, and seven years later, in 1867, there were 
more than 40 establishments, with an annual product worth $400,000. 

The development of the tanbark industry since 1850 is shown by 
Table 1. 

TABLE I. Tan oak bark harvested in California, 1855 to 1907. 



Annual product. 


Annual product. 


Product by periods. 


Year. 


Cords. 


Yar. 


Cords. 


Years. 


Cords. 


1855 


1,000 
3,000 
8,000 
15,000 
21,000 
24,000 
24,000 


1893 


20,000 
20,000 
25,000 
30,000 
25,000 
30,000 
20,000 


1851-1860 


15,000 
.55,000 
147,500 
240,000 
218,500 
185,000 
861,000 


1860 


1895 


1861-1870 


1870.. . 


1900 


1871-1880 


1875 


1904 


1881 1890 


1880 


1905 


1891-1900 


1881 


1906 


1901-1907 (7 years) 
1851-1907 


1890 


1907 







i In gathering the data upon which this report is based the author received assistance and helpful courte- 
sies from many people directly or indirectly connected with the tanbark industry on the Pacific coast. 
Their number was too great to permit of individual acknowledgment here, but the author takes this means 
to thank them for the great assistance given him. 

5 



CALIFORNIA TAXBARK OAK. 



At $18 per cord, an average of the prices since 1850, the value of 
the bark produced in the period 1851-1907 would be $15,498,000. 
Practically all of this has been consumed in the manufacture of heavy 
leather used for belting, harness, saddles, and soles. The California 
tanneries, up to 1907, turned out 250,000,000 pounds of such leather, 
valued at $75,000,000. 

SILVICAL CHARACTERISTICS OF THE TANBARK OAK. 

Tanbark oak (Quercus densiflora H. & A.) grows to be from 50 to 
140 feet high and from 1 to 6 feet in diameter. There are four general 
forms of growth the roundheaded; the spire-shaped, similar to coni- 
ferous trees; the shrubby, deep-shade form; and the stunted cha- 
parral form. In open situations, or in association with madrona and 
California black oak, the main trunk subdivides into a number of 
large branches and forms a rounded head, although the height of the 
crown is greater than its width. In dense, coniferous forests it 
assumes the spire or cone shape of the trees with which it is associated, 
and these trees are tallest and have the straightest trunks, with a 
clear length of from 30 to 80 feet. Under stands of mature Douglas 
fir or redwood there may be abundant low, shrubby growths of tan- 
bark oak, since the tree is remarkably shade enduring, and when the 
dominant forest cover is removed the tanbark oak promptly takes 
possession of the logged areas. This is exemplified especially on the 
Mendocino coast. In the interior of California, around Mount Shasta, 
the stunted tanbark oak in the midst of chaparral assumes many of 
the characteristics of the shrubs by which it is surrounded, such as 
low stature, rigid branches, and small, thin leaves. This chaparral 
form (var. ecJiinoides) is worthless for tanbark. 

Tanbark oak has many chestnutlike characteristics. In the 
character of its male flowers the tree is a chestnut, but in the character 
of its female flowers and in its habit it is an oak. By some authors 
it is referred to the genus Pasania, which includes nearly 1 00 species 
in southwestern Asia. 

The oaklike characters and the chestnutlike characters are com- 
pared in the following tabulation: 



CHESTNUTLIKE CHARACTERS. 

Parallel nerves of the toothed leaves. 

Erect catkins. 

Pistillate flowers in same catkins as 
staminate. 

Stamens of male flowers very much ex- 
ceeding calyx; rudiments of stamens in 
pistillate flower. 

A. corns with suggestion of burriness. Nut 
often vaguely triangular. 



OAKLIKE CHARACTERS. 

Bark very like typical oak bark. 
Involucre 1-flowered. 
Ovary 3-celled. 



Cup of the acorn a true cup and not a 
closed involucre. Kernel oaklike, bit- 
ter to the taste. 



SILVICAL CHARACTERISTICS. 7 

The chestnutlike leaves are from 2 to 5 inches long and are borne 
on short petioles. The teeth are small and scattered. Sometimes 
the margin is entire near the base or even for its whole extent, 
especially on narrow-leaved forms. This variation in leaf form 
sometimes leads woodsmen to speak of "two kinds of tanbark oak." 
Both surfaces of the leaf, especially the lower, are covered with a 
thick, light-colored, dusty fuzz, which gives the foliage a distinctive 
hue. 

The flowers, which appear in July or August, often conceal the 
foliage with a mass of grayish-white blossoms. The acorns are 
from f inch to 1J inches long, and from f to 1 inch broad, and coated 
with a brown fuzz. The somewhat burrlike but shallow cup is 
covered with long and narrow scales. 

The bark of the trunk of adult trees is usually from 1 to 3 inches 
thick, and sometimes from 4 to 5 inches; it is brown, smooth on 
the surface, but so fissured longitudinally and transversely as to 
produce elongated, irregularly rectangular plates. On the main 
limbs and on young trunks the bark is very smooth, little fissured, 
if at all, white, gray, or mottled, and often strikingly similar to the 
bark of red alder. 

RANGE AND OCCURRENCE. 

The range of tanbark oak extends from a little north of the 
Umpqua River in southwestern Oregon through the coast ranges to 
Santa Barbara in California, and from the Humboldt region eastward 
by way of the Shasta Mountains to the Sierra Nevada, and along 
that range as far south as El Dorado County. 

In general, though not always, tanbark oak grows either with 
redwood or in the neighborhood of the redwood belt. It is an 
associate of redwood in all the great redwood areas and even in the 
isolated bodies or tongues in the range of that tree. The greatest 
forests of redwood are in Mendocino and Humboldt Counties, and 
in those counties tanbark oak attains its best development. (PL II.) 
Tanbark oak is not at its best, however, in the heart of the redwood 
forests, but in the belts which border them. The principal body of 
tanbark oak forms a band along the inland side of the redwood belt 
and covers the "Bald Hills." The general term "Bald Hills" 
is a widely used folk name for the inland portion of the seaward Coast 
Range, that much-broken mountain range which parallels the coast 
and separates the ocean from such valleys as those of Santa Rosa, 
Alexander, and Ukiah^nd the narrow canyon of the main Eel River 
in its long course from Little Lake Valley northward to Humboldt. 

The higher inner ridges and summits and the interior slopes are 
covered by a mixed forest forming the tanbark oak belt along the 
whole length of the main redwood body. In southern Humboldt, 



8 CALIFORNIA TANBARK OAK. 

however, the tanbark oak belt pushes through the great transverse 
break in the redwood belt at that point, and an arm extends north- 
ward over the Wilder Ridge country to the Rainbow Range. This 
extensive and excellent virgin body borders the redwood belt on the 
outside and covers a considerable portion of the Mattole country 
lying between the redwood belt and the ocean. 

In the region around Eureka the redwood stand is so exceedingly 
dense that it practically occupies the whole country to the exclusion 
of tanbark oak. In the redwood forests along the main Eel River, 
on the Mad River, and on Smith River tanbark oak grows not at all 
or merely as tare individuals. Here it is necessary to pass through 
the redwood belt, or, what is usually the same thing, to gain the 
summits of the ridges at the headwaters of the coast streams, to 
find tanbark oak. To the south this is not the case. In Mendocino 
County tanbark oak occurs throughout the redwood belt. There, 
however, tanbark oak trees in the main redwood stands areisually 
small and scattering, and it is only on the summits above the redwood, 
and particularly on the inner summits and ridges, that the trees are 
abundant and of large size. 

ASSOCIATES. 

Tanbark oak never forms a pure stand. The tanbark oak belt 
consists of a mixed forest of broadleaf and coniferous trees. Its 
most common associates besides redwood are Douglas fir, which, 
except in Santa Barbara County, occurs with it throughout its 
range; madrofia (Arbutus menziesii), its most common associate, 
which reaches very large dimensions in the tanbark oak belt; Oregon 
post oak (Quercus garryana), the most abundant of the true oaks in the 
whole tanbark oak belt; California black oak (Quercus calif ornica) , 
on all the higher ridges, or high, fertile hill slopes; and western 
chinquapin (Castanopsis chrysophylla) , an associate in the regions of 
its best development. 

THE PRODUCTION OF TANBABK. 
CENTERS OF THE INDUSTRY. 

The Santa Cruz district has been, from the first, one of the most 
important sources of tanbark, because the tanneries at Santa Cruz, 
San Jose, Santa Clara, and Redwood City could be supplied by 
wagons direct from the woods, and this obviated long and costly 
shipment by rail or water. Seventy-five per cent of the original 
stand has been peeled, but recently second-growth trees have begun 
to furnish a bark which is acceptable to tanners. Sonoma County 
has been an important source for 30 or 40 years, and its status 
now is about the same as that of the Santa Cruz district. For the 



Bui. 75, Forest Service, U. S. Dept. of Agriculture. 



PLATE II. 




OCT29I9I4 

of Forestry 



PRODUCTION OF TANBARK. 9 

last 17 years the chief source has been the Mendocino district, along 
the coast to the north of Sonoma, where tanbark has been outranked 
only by redwood as a valuable forest product. This region has 
furnished probably more bark than all others put together, but 45 
per cent of the stand has been peeled now and a considerable portion 
of the remainder is, under present conditions, too inaccessible to be 
of value. The stand in the Santa Lucia Mountain region, along the 
coast in Monterey County, which, though of excellent quality, was 
never large, is now almost exhausted. In the isolated Santa Bar- 
bara district and in the Sierra Nevada territory the trees are few and 
scattered. 

The most extensive bodies of virgin tanbark oak now are in the 
north in northern Mendocino and Humboldt Counties and because 
of accessibility to shipping the main sources of supply are in the coast 
region of Mendocino, southern Humboldt, and, to some extent, 
Sonoma Counties in California, and in southwestern Oregon. The 
Sonoma and Mendocino areas have been drawn upon from the inte- 
rior, also, by a railroad which follows the valleys of Santa Rosa, 
Russian River, and Little Lake northward, and has now reached 
the center of Mendocino County. The most northern part of the belt 
has not been much disturbed, since the railroad has not reached it 
and its distance from the ocean necessitates a long haul. The tan- 
neries at Humboldt Bay have been supplied from Kneeland Prairie 
and the Acorn region in the Bald Hills country. 

STAND AND YIELD. 

It is estimated that 'there are now 1,425,000 cords of standing bark 
in the Pacific coast forests, distributed as follows: 



Counties. 



Cords. 



California: 



San Mateo, Santa Cruz, and Monterey 

Marin, Sonoma, and Napa 

Mendocino . : 

Humboldt, Trinity, western Siskiyou, and Del Norte 



Oregon: 



100,000 

70,000 

320,000 

87,5,000 



Curry and Coos. 



60,000 



Total.. 



1,425,000 



At the present rate of consumption, this is enough to provide for 
the needs of the leather industry in California for a little less than 
half a century. 

The average yield of bark is from 200 to 350 cords per "claim," 
or quarter section (from 1J to 2^ cords per acre). From 350 to 640 
cords (from 2J to 4 cords per acre) is considered a particularly good 
yield, and exceptionally fine quarter sections yield from 640 to 1,200 
cords (from 4 to 7J cords per acre). The highest yields are not 
89446 Bull 7511 2 



10 



CALIFORNIA TANBARK OAK. 



uncommon in the best parts of the southern Humboldt and northern 
Mendocino district, where the stand in limited areas is nearly pure 
tanbark oak. The largest amount of bark ever reported from* one 
"claim" was 1 ; 284 cords, or 8 cords per acre. 

In estimating tanbark in the Santa Cruz, Mendocino^and southern 
Humboldt districts cruisers generally count 6 tree^to the. cord, 
though sometimes the trees are so large that it takes 'only 4*ito pro- 
duce a cord. In the northern Humboldt' district 8 or 9 trees /make 
a cord and hi the Klamath 14. Cruisers are more likely to under- 
estimate than to overestimate a claim. Exceptionally large trees 
with thick bark produce from 2 to 3J cords of**bark. The figures 
given in Table 2 are from trees on the inner edge of' the redwood belt. 

TABLE 2. Amount of tanbark on oak trees of different sizes. 



Diameter, 


Height. 


Length of 
peeled 
trunk. 


Diameter 
of peeled 
trunk at 
upper end. 


Age. 


Weight of bark. 


Dry weight of 
bark (calcu- 
lated). 


Inches. 


Feet. 


Feet. 


Inches. 


Years. 


Pounds. 


Pounds. 


4- 9 


30- 50 


4- 8 


3- 6 


20- 40 


15- 80 


10- 70 


10-12 


40- 80 


16-32 


5- 8 


40-100 


80- 350 


70- 250 


13-18 


80-100 


32-65 


7-12 


70-125 


350- 900 


250- 650 


19-24 


90-120 


65-80 


7-11 


100-159 


900-1,700 


650-1,200 


24-36 


115-140 


80-95 


9-11 


125-180 


1,700-2,500 


1,200-1,800 


36-48 


100-120 


80-90 


9-18 


350-210 


2, 500-4, 000 


1,800-2,800 


48-60 


100-120 


80-90 


9-18 


170-250 


3, 500-8, 000 


2, 500-5, 700 



To avoid discrepancies due to loose piling, the "cord" used in 
selling tanbark is reckoned by weight rather than by dimension, and 
is approximately a ton, though it varies in different localities from 
2,200 to 2,600 pounds. It is most commonly 2,400 pounds, which is 
the standard accepted in San Francisco. For bark that has been 
peeled a year, 2,300 pounds is considered a ton. Very rarely a cord 
is measured by dimensions; but where it is, as at Arcata, for instance, 
it is 8 feet long, 4 feet wide, and 4| feet high. 

PEELING. 

The peeling season runs from about May 20 to about August 10, 
but varies with latitude, weather, and locality. Peeling can be 
started any time after the sap begins to run and continues during the 
period of summer growth. Tanbark oak is extremely sensitive to 
heat and cold as regards the adhesion of its bark. A cold spring 
-delays the opening of the peeling season and a cool, moist summer 
prolongs it. Trees on the shady north slopes will peel later than 
those on the ridges or south slopes, but one of the periodic north 
winds of the Coast Range, which are hot and dry, will make peeling 
difficult or cause some trees to bind down completely. Cold nights, 
on the one hand, will make the bark stick, and a hot period in July or 
August will put an end to peeling. Trees standing side by side often 



PRODUCTION OF TANBARK. 11 

show different sensitiveness to weather changes; even two sides of a 
tree may differ in ease of peeling and the north side stick before the 
other. 

Peeling is also affected by injury from fire, wind, or snowstorms. 
Trees which are only slightly hurt by fire will not peel for two or three 
seasons, and sometimes not at all. The wounds made when limbs are 
broken off by windstorms or by the weight of snow have a similar 
effect. Even the "try marks" on trees which are found not ready to 
peel interfere with satisfactory work later in the season. 

Peeling can be done more economically in the latter part of the 
season because the bark, which is brittle in the early part, becomes 
tougher then, so that it can be taken off in entire pieces. 

At least half a day is required for two men to peel a large tree. The 
peelers, therefore, never begin late in the day upon a tree which they 
must leave unfinished until the next morning, as the bark may " bind 
down" overnight. 

The peelers work in pairs. Usually they rely on the woodsman's 
one-edged ax alone, as they believe that the advantages of a spud 
do not equal the saving of time when the ax alone is used. With the 
blade of his ax the peeler tries the bark to determine if it is loose, 
and if it is he cuts two circles through the bark, one at the foot of the 
trunk, the other 4 feet above. The bark is then slit longitudinally 
and taken off in from one to four pieces. (PL III.) The circle of bark 
thus removed is called a " rim" or a " coil." The first coil is removed 
from the standing tree because it is easier to work when the tree is 
erect and because it prevents the loss in chips at the base of the tree, 
where the best bark is. In felling, the woodsman takes advantage 
of the lay of the land, of down logs, and of gullies, in order that the 
trunk may not lie flat on the ground and interfere with the removal 
of the bark. Most tanbark oak trunks are badly fire-hollowed, which 
makes it difficult to place them accurately. After the tree is down 
the small branches are lopped/and interfering shrubs are brushed out. 
One man then goes ahead "Hnging," or cutting through the bark 
around the trunk; the second man follows, slits the bark, and removes 
the coils. This process is continued up the trunk until the bark 
becomes less than one-half inch thick. As the "coils" are taken off 
they are laid on the ground with the inner or "flesh" side up, where, 
as they become dry, they harden and curl up. 

The average woodsman peels from 1 to 1J cords per day. Where 
the stand consists of trees with straight, clear trunks standing on 
ridges, an expert peeler can cut from 4 to 5 cords in a day. In the 
case of very limby trees it is a general practice to take the bark off 
only the clear portion of the trunk and abandon much of the remaining 
bark even where it is thick. The quality of such waste is shown by 
the analyses given in Table 3. 



12 



CALIFORNIA TANBARK OAK. 
TABLE 3. Analyses of bark wasted in abandoned tops. 



Origin of samples. 


Solids soluble in cold water. 


Solids 
soluble 
in hot 
water 
only, 
reds. 


Total 
solids. 


Tannin. 


Non- 
tannin. 


Total. 


1. Sample taken 3 feet beyond last coil removed by 
peelers 


Per cent. 
17.29 

15.64 


Per cent. 
13.08 

11.82 


Per cent. 
30.37 

27.46 


Per cent. 


Per cent. 
30.32 

27.56 


2. Sample taken 8 feet beyond last coil removed by 
peelers 


0.10 





Although peeling into limby crowns adds disproportionately to the 
expense because of the thinner bark and the extra trouble to get it, 
nevertheless waste could be lessened economically through closer 
supervision of the peelers. 

It is customary to peel all the trees, even down to poles from 3 to 8 
inches in diameter. One or two coils are taken from these poles 
without felling them. This practice, called "jayhawking," also leads 
to waste in bark. The two coils, which can be taken off without 
cutting the tree down, do not always include all the bark worth 
taking. In some districts " jayhawked" trees are frequent with clear 
trunks for 20 feet above the last coil taken and bark three-quarters 
of an inch thick. The quality of such waste is shown by the analyses 
given in Table 4. 

TABLE 4. Analyses of bark left on "jayhawked" trees, southern Humboldt County. 



Description of tree. 


Diame- 
ter at 1 
foot. 


Total 
height. 


Solids soluble in cold water. 


Solids 
soluble 
in hot 
water 
only, 
reds. 


Total 
solids. 


Tannin . 


Non- 
tannin. 


Total. 


1. Two co Us taken by peelers; sam- 
ple from Just above second coil. . 
2. One coil taken by peeler; sam- 
ple from just above coil 


Inches. 
8 

3.5 
9 


Feet. 
50 

25 
55 


Per cent. 
13.05 

13.85 

10.12 


Per cent. 
6.71 

7.15 
6.72 


Per cent. 
19.76 

21.00 
16.84 


Per cent. 
0.09 

.44 


Per cent. 
19.85 

21.44 
16.58 


3. Two coils taken by peelers; 
bark, sample from just above 







TRANSPORTATION. 

The bark curls up hi three weeks and is then tough enough to 
stand handling. It is "bunched" or gathered together in small 
regular piles. The swampers cut narrow sled roads through the 
woods to the bunches of bark and it is sledded to the wagon road, 
where it is corded up. In some districts the bark is carried out on 
mule back, loaded on iron panniers. 

After the bark is sledded a woodsman is sent through the woods to 
sack the chips and search for bark which has been overlooked or 



Bui. 75, Forest Service, U. S. Dept. of Agriculture. 



PLATE III. 





** 



Bui. 75, Forest Service, U. S. Dept. of Agriculture. 



PLATE IV. 




FIQ. 1. PEELING 4-Foor RINGS OF BARK FROM THE FELLED TREE. 




FIG. 2. BUNCHING THE BARK IN SMALL PILES ALONG THE SLED ROAD. 



Bui. 75, Forest Service, U. S. Dept. of Agriculture. 



PLATE V. 




FIG. L-THE SKIDWAYS TO WHICH THE BUNCHED BARK is SLEDDED, AND FROM WHICH 
IT is HAULED TO THE RA/LROAD. 




FlQ. 2.-HAULING THE BARK IN WAGONS FROM THE SKIDWAYS TO THE CARS. 



PRODUCTION OF TANBARK. 



13 



covered up by the tops of the tress, but even with this precaution, 
here and there bark piles are left whenever the peelings are extensive. 
Chipped bark, which comes chiefly from the base or "rump" of the 
tree, is the richest of all in tannin, and, on account of its greater weight 
and smaller bulk than coil bark, particularly desirable. But it is 
much more likely to be scattered and overlooked in the woods, and 
it would be better woods practice if this bark were piled immediately 
on peeling and sacked just before the coil bark is bunched. The cost 
would be no greater than- in all probability not as much as by the 
present method. The tannin quality of rump bark is shown in 
Table 5: 

TABLE 5. Analyses of the tannin quality of rump baric. 



Locality. 


Solids soluble in cold water. 


Solids 
soluble 
in hot 
water 
only, 
reds. 


Total 
solids. 


Tannin. 


Non- 
tannin. 


Total. 


Southern Humboldt County 


Per cent. 
29.20 
20.89 


Per cent. 
12.86 
6.97 


Per cent. 
42.06 
27.86 


Per cent. 
2.86 
3.26 


Per cent. 
44.92 
31.12 


Santa Cruz County 





On the Sonoma and Mendocino coasts the tanbark is usually trans- 
ported to the ocean by the steam logging railways, which follow the 
courses of the numerous rivers and creeks. These roads were built 
primarily to carry redwood, but have cars with frames for tanbark. 
The Mendocino coast is rockbound and there are no real harbors, but 
only open roadsteads or half-sheltered coves. The cars are run out 
upon a headland, and the frame, with its load, is lifted by a steam 
derrick and transported by a cable to a schooner offshore. A schooner 
that carries 200 cords of bark may be loaded thus in a very short time. 
Nearly all of the bark shipped by schooner from the Mendocino coast 
goes to the San Francisco Bay tanneries. 

Sometimes tanbark is transported to the coast by four-horse wagons, 
which have a capacity of from 2 to 4 tons. 

The bark delivered for shipment must be air-dry and, according to 
the rules, must not include any "paper bark" or "snake skin" that 
is, bark less than half an inch thick. In practice, however, thin bark 
is included in the shipments without arousing protest, provided there 
is not too much of it. In the hot, rainless summers of the Coast Range 
there is no difficulty in meeting the requirement that the bark be 
air-dry. Bark rarely reaches the market in less than from four to 
eight weeks from the tune of peeling. Heavy bark loses from 25 to 
30 per cent of water in this period, medium bark from 30 to 35 per 
cent, second growth and paper bark from 35 to 40 per cent. There 
is also a slight loss, from 0.5 to 1 per cent, due to breakage in han- 
dling and shipping. 



14 



CALIFORNIA TANBARK OAK. 



The long dry season of California is highly favorable to the tanbark 
industry , since it obviates precaution against rain. Bark held over 
winter must be sheltered, since more than 25 per cent of tannin is 
leached out by rain in one winter. Dampness also causes mold, 
which injures the leather and is difficult to get rid of. 

QUALITY OF THE BARK. 

The proportion of tannin varies with the part of the tree from which 
the bark is taken and with the local and geographical situation of the 
tree. Old bark near the base of the trunk contains the highest pro- 
portion. The color of a cross section of fresh bark is an index of the 
quality in this respect ; bark richest in tannin is a deep red, while the 
poorest is pale or yellowish. Bark is not considered ripe until it has 
formed three layers, a rougher outer "ross," a central "meat," and 
an inner "fiber." Before it has divided thus the tannin content is 
low. Trees in virgin stands arrive at this maturity at from 55 to 70 
years of age. 

The variation in bark quality on a typical tree is shown in Table 6 : 

TABLE 6. Analyses showing distribution of tannin from the base to the top of the tree. 1 



Location of sample. 


Thick- 
ness of 
bark. 


Solids soluble in cold 
water. 


Solids 
soluble 
in hot 
water 
only, 
reds. 


Total 
solids. 


Tan- 
nin. 


Non- 
tannin. 


Total. 


Rump 


Incht 
li 
1 

1 
1 

i 

i 


5. 

>, 
s, 


Per ct. 
29.20 
25.77 
19.93 
16.13 
19.37 
13.16 
13.21 
10.00 
12.50 
10.82 


Per ct. 

12.86 
12.72 
10.76 
9.26 
11.63 
9.40 
8.17 
6.78 
9.42 
8.42 


Per ct. 
42.06 
38.49 
30.69 
25.39 
31.00 
22.56 
21.38 
16.78 
21.92 
19.24 


Per ct. 
2.86 


Per ct. 
44.92 
38.49 
30.69 
25.39 
31.16 
22.56 
21.38 
16.78 
21.92 
19.24 


First "cut 


15 feet 


31 feet 




45 feet 


0.16 


60 feet 


66 feet. 




74 feet 




78 feet.. 




84 feet 









1 Tree 18 inches in diameter 4 feet from the ground, and 96 feet high, in northerly h'ollow, southern Hum- 
boldt County. 

Sunshine and light increase the secretion of tannin. For this 
reason the best bark grows on ridges, and the southern districts yield 
a richer product than the northern. Bark from the Santa Lucia 
Mountains, the southernmost of all the districts, is the richest in the 
market and averages as high as from 20 to 24 per cent. According 
to the tanners who have used bark from widely separated districts, 
that grown in the "Bald Hills" district in the interior, beyond the 
influence of the sea fogs, is richer than that from the coast, where the 
trees are shaded by redwoods and are in the fog belt. Bark from the 
coast of Oregon is low in tannin, with an average of only 12 or 14 
per cent. 



PROLONGING THE SUPPLY. 



15 



Table 7 shows the results of analyses of bark of representative trees 
of the various districts: 

TABLE 7. Analyses of bark samples from different districts. 



Bald Hills districts. 


Solids soluble in cold water. 


Solids 
soluble in 
hot water 
only, 
reds. 


Total 
solids 
extract. 


Tannin. 


Nontan- 
nin. 


Total. 


Thick bark, commercial sample, Briceland, Hum- 
boldt County 


Per cent. 
24.74 
14.82 
14.90 

15.66 

15.36 

20.51 

22.20 
14.92 
14.00 
16.20 
22.73 

19.08 

21.61 
18.93 
18.24 


Per cent. 
13.18 
9.60 
11.86 

7.12 
10.02 

11.21 

11.69 
8.89 
6.73 
8.92 
10.07 

9.76 

6.85 
5.40 
9.24 


Per cent. 
37.92 
24.42 
26.76 

22.72 
25.38 

31.72 

33.89 
23.81 
20.73 
25. 12 
33.80 

28.84 

28.46 
24.33 

27.48 


Per cent. 
3.08 
1.78 
2.16 

2.52 

1.88 

3.24 

2.87 
1.15 
1.86 
3.76 
1.14 

7.96 

2.14 
2.67 
3.60 


Per cent. 
41.00 
26.20 

28.92 

25.24 
27. 26 

34.96 

36. 76 
24.96 
22.59 
28.88 
34.94 

36.80 

30.60 
27.00 
30.08 


Thick bark, Acorn region, llumboldt County 


Thin tfark, Acorn region, llumboldt County 


Between Low Gap and Summit, west of Ukiah: 
It-foot tree, sample at 3 feet from ground, ridge 
tree 


ly-foot tree within 15 feet of preceding 


Just east of Coast Range summit (west of Ukiah); 


Elk Creek, Mendocino County: 
Thick bark > 


Medium bark . 


Thin bark 


Ridge tree in open, near coast at Kenny's; 2-foot tree. 
Ridge tree near coast at Kenny's' 2-foot tree 


South slope tree exposed to sun, Halfway House, 
Ukiah-Mendocino Road; 2-foot tree 


San Vicente Creek, Santa Cruz Mountains, Redwood 
district: 
3-foot smooth-barked tree 


Rough-barked tree within 10 feet of preceding; 
2i-foot tree 


San Vicente Creek, Santa Cruz Mountains, S.Woot 
tree 





PROLONGING THE SUPPLY. 

With the disappearance of the bodies of tanbark oak which have 
furnished the chief tanning material for the leather manufacturing 
industry on the Pacific coast the question of the continuation of the 
supply becomes very important. Since the greater portion of the 
standing tanbark is now confined to broken and inaccessible moun- 
tain country, the extension of transportation facilities to those 
regions must exert a very marked influence on its exploitation and 
cost. Railroads and wagon trails are being rapidly pushed into the 
northern coast ranges, and it is probable that within two or three 
years the rich belts of Mendocino, Humboldt, and Del Norte Counties 
will have at least one railway line. The utilization of second growth; 
the introduction of more conservative methods in the woods, par- 
ticularly in connection with the redwood lumbering industry; the 
protection of the forests from fire; and the extension of the use of 
other products as substitutes for and supplements of the bark of 
this most important tree, will all have their influences on the future 
supply. 



16 CALIFORNIA TANBARK OAK. 

PROVIDING FOR SECOND GROWTH. 
SPROUT REPRODUCTION. 

For the maintenance of the supply of tanbark on the Pacific coast 
the second growth on cut-over areas offers by far the most hope. 
Sprout reproduction must be encouraged, since the tree sprouts very 
readily and with great persistence. Sprouts grow from trees of prac- 
tically Siuy age and under a wide variety of conditions. Of greatest 
economic significance are those which spring up from the stumps of 
trees felled for peeling. The sprouts arise from conical woody buds 
which are formed under the bark at the base of the tree, and which 
vary in number from a scattering few to crowded thousands. The 
sprouts themselves vary in number; as many as 1,400 have been 
counted on one large stump. The practice of peeling the tree down 
as far as possible, often below ground level, in order to obtain all the 
rich and heavy rump bark, exposes the buds and prevents sprouts, 
but peeling can safely be carried down to the surface of the ground 
if the peelers ring the bottom of the first run instead of stripping off 
the bark as far down as it can be torn. The original number of 
sprouts is reduced by natural processes in 30 years to from four to 
eight of the most vigorous poles. The rate of height growth is about 
2 feet a year. By proper thinning this rate could be accelerated. 

Sprouts also come up freely about the base of fire-injured and even 
fire-killed trees, which is a great advantage where there are frequent 
forest fires, as in the tanbark oak regions. They even grow vigor- 
ously from the stumps of old trees which have been weakened by 
dry rot or fire and have fallen. The Stumps of such fallen veterans 
may be a yard or two in diameter. Circles of sprouts about the rims 
of such stumps which have disappeared are often found in the woods, 
and the trunks of these sprouts are sometimes 2 feet in diameter at 
4 feet from the ground. Sometimes sprouts will start from the base 
of living trees, though this habit is of slight commercial importance. 

Nothing can better illustrate the vitality of tanbark oak than the 
longevity of standing trees which have been peeled. Peeling is 
usually done before flowering time, and for the first year afterwards 
the growth of the tree is so decidedly checked that it does not fruit. 
The second year the tree bears a full crop of acorns often an exces- 
sively large crop. The woodsmen call this the "last kick" of the 
tree, since in the third year it usually dies. If the tree stands exposed 
to the full heat of the sun it will probably die the first season. Yet 
there is abundant testimony that it may continue to live for a long 
period even 10 or 15 years. The apparent anomaly of a tree con- 
tinuing its life functions with a complete band of bark removed from 
its trunk can be explained by a study of "jayhawked" trees in the 
field. Such trees were peeled either so early in the season or so late 



PROLONGING THE SUPPLY. 17 

in the season that the bark did not part readily from the wood, and 
a very thin portion of the inner bark and cambium layer adhered to 
the wood and formed a sort of film. This film after one season looks 
like a thin ooat of brown varnish. The wood beneath, however, is 
greenish and pulpy, suggesting the mesophyll layer of a leaf. This 
layer does not increase appreciably in thickness. 

REPRODUCTION BY SEED. 

No other oak on the Pacific coast produces so heavy a crop of 
acorns as tanbark oak, but seedlings, nevertheless, are not abundant. 
In the main, forest seedlings are found only where a fallen tree has 
made a break in the forest canopy and let in light. The "Bald 
Hills" country is filled with hogs and cattle, which prevent seedling 
reproduction by devouring the acorns and browsing the tender foli- 
age of the young growth. 

Attempts at artificial . propagation outside the natural range of 
tanbark oak have failed. The acorns germinate in open nursery beds 
in about five weeks. The seedlings come up a little more promptly 
in loam beds than in adobe, but those in the adobe seem a trifle more 
vigorous than the others. Sand beds germinate only 2 per cent of the 



Eighty per cent of the seeds planted in 1902 at the California For- 
estry Station at Chico germinated, but not one seedling survived the 
first summer, although the soil conditions are favorable. The hot, 
dry climate of the interior valleys does not furnish a normal environ- 
ment for tanbark oak, and the formation of plantations is practica- 
ble only where conditions are similar to those of the natural range 
of the tre*e. 

SECOND-GROWTH BARK. 

For several years second growth has been peeled in the Santa Cruz 
Mountains, and it is claimed by some owners who superintended both 
peelings that the yield of second growth exceeds that of the virgin 
stand. There is nothing to prove or disprove this assertion, but it 
is probable that these men did not take account of the fact that the 
harvesting of the crop to-day is very much closer and more careful 
than the peeling of the virgin timber from 30 to 50 years ago, and 
that "passed trees" of the virgin stand were stripped at the sec- 
ond peeling. Although it is improbable that the yield of second 
growth at the end of 30 years would equal that of the original 
stand, it is sufficiently heavy to make the holding of cut-over lands 
profitable for repeeling in 30 years, when from 1 to 5 cords per 
acre can be harvested. 

Table 8 gives the yields of a number of second-growth trees in the 
Santa Cruz Mountains. 

89446 Bull. 7511 3 



18 



CALIFORNIA TANBARK OAK. 



TABLE 8. Amount of bark on second-growth tan oak, age 29 to 31 years, Santa Cruz 

Mountains. 



Height 
of tree. 


Diame- 
ter of 
trunk at 
2 feet. 


Length 
of peeled 
trunk. 


Diame- 
ter of 
trunk at 
end of 
last coil. 


Thick- 
ness of 
bark at 
butt. 


Weight 
of bark, 
green. 


Weight 
of bark 
dry (cal- 
culated). 


Feet. 


Inches. 


Feet. 


Inches. 


Inches. 


Pounds. 


Pounds. 


52 


7 


24 


4 


U 


145 


91 


50 


6 


24 


4 


1J 


143 


90 


62 


10 


24 


6 


li 


241 


152 


55 


7 


20 


4 


I* 


125 


79 


65 


9 


28 , 


6 


2 


. 243 


152 


55 


7 


20 


, 5 


11 


120 


76 


62 


8 


- 24 


5 


l| 


158 


100 


62 


7 


24 


5 


I* 


160 


101 


60 


8 


28 


6 


2 


235 


148 


65 


10 


28 


6 


i 


303 


191 


70 


9 


28 


6 


i 


303 


191 


67 


10 


36 


5 


2" 


321 


202 


68 


9 


36 


5 


| 


241 


152 


67 


9 


32 


5 


{ 


208 


131 


65 


8 


32 


5 




177 


112 



QUALITY OF SECOND-GROWTH BARK. 

Tanners estimate that second-growth bark will average only 10 per 
cent tannin, and when it was first put upon the market they objected 
to it; but, mixed with virgin bark, it is now used to a considerable 
extent. It is distinguishable from virgin bark by its peculiar smooth- 
ness both on the outside and the inside; by its brittleness, due to lack 
of fiber, especially toward the inside, where virgin bark is so fibrous; 
and by its sappiness and light color. 

Table 9 shows the characteristics of samples taken from near the 
bases of trees. The thinner bark higher Up would, of course, lower 
the average. 

It is possible to produce a good quality of leather by tlie use of 
second-growth bark alone, but a large quantity is required to offset 
its low tannin content. The item of labor is also greater, since it costs 
more to handle the extra bark. 

TABLE 9. Analyses showing tannin content of tan-oak bark taken from thr& 'Second- 
growth trees. 



Locality. 


Height. 


Diame- 
ter of 
wood at 
1 foot. 


Age. 


Solids soluble in cold water. 


Solids sol- 
uble in 
hot water 
only, 
reds. 


Total 
solids. 


Tannin. 


Nontan- 
nin. 


Total. 


Between Comptche 
and Low Gap, one of 
16 sprouts about 
stump 


Feet. 
Mi 

'40 
60 


Inches. 
2* 

5 
9 


Years. 

7 

24 
30 


Per cent. 
18.28 

16.22 
14.10 


Per cent. 

8.28 

10.60 
8.94 


Per cent. 
26.56 

26.82 
23.04 


Per cent. 
1.00 

, -56 
.52 


Per cent. 
27.56 

27.38 
23.56 


Between Comptche 
and Low Gap 

San Vicente Creek, 
Santa Cruz Moun- 
tains 





PROLONGING THE SUPPLY. 19 

CONSERVATIVE METHODS IN THE WOODS. 

Redwood lumbering has done much to keep the annual supply of 
tanbark steady and to make remote stands accessible. It is the 
practice of the redwood lumber companies to send tanbark crews 
through the woods in advance of the redwood logging crews, since the 
firing of the district, which always follows felling, to facilitate the get- 
ting out of the redwood logs by wire cable and donkey engine, badly 
injures all standing trees, and even if it does not actually destroy the 
tanbark oak it makes peeling .difficult or impossible. 

GUARDING AGAINST FIRE. 

Up to the present time no attention has been paid to the future 
condition of the forestf in which peeling has been carried on. Yet the 
introduction of conservative methods would prevent a very large 
waste. Fire, which always accompanies redwood logging, makes it 
an economical policy to take all the bark possible, whether the .tree 
has reached maturity or not. Under conservative methods " jay- 
Hawked" trees, which yield only from 10 to 60 pounds of bark with 
a low tannin content, would in 10 or 20 years form profitable elements 
in the new stand for both bark and wood. Despite the custom of 
taking all the bark that can be peeled without regard to whether it 
is mature or not, the maximum yield is never obtained under present 
methods. Some trees which will not for one reason or another peel 
readily in one season, although they would a year or two later, are 
sacrificed in order to chip a little bark off their trunks or to secure one 
or more coils because the trees are considered as doomed to fire any- 
way. Often from 70 to 90 per cent of the bark in such cases can not 
be taken from the tree. Moreover, the fires kill very young trees, kill 
sprouts down to the stumps, and seriously interfere with reproduction. 
Under conservative management the older trees would be saved for 
peeling in a favorable year and the younger ones permitted to develop 
a new stand. As tanbark oak always grows in mixed stands, the 
holding of redwood and Douglas fir lands for a second crop would 
give the tanbark oak the necessary fire protection and would furnish 
a profitable element in the later harvests. 

During the rainless season in California, from May to October, even 
in the foggy coast region, fires caused by logging crews, hunters, 
campers, and in the far north coast ranges by thunderstorms, lead to 
several million dollars damage every year. These fires rarely kill tan- 
bark oak trees, but make long vertical wounds from 4 to 10 feet up 
the sides of the trunks. On young trees these injuries are often com- 
pletely covered by the meeting of new bark growth, but with trees 
more than 100 years old the sides of the' wound usually spread. The 
exposed wood rots, andsucli trees, called " goose pens," are difficult 



20 CALIFORNIA TANBARK OAK. 

to lay out accurately in felling. Even a slight injury to the trunk 
permits the entrance of fungi which weaken the wood, and the loss of 
such trees in heavy snowfalls is very large. 

Trees on slopes or canyon sides are the greatest sufferers; 95 per 
cent of the tanbark oak trees in those positions are injured by fire 
and 80 per cent fire hollowed. In the case of ridge trees, about 80 
per cent are comparatively free from fire hollows, because a fire 
traveling up a slope is either running high or going out when it 
reaches the top. 

The most extensive destruction by fire in the tanbark oak belt 
has probably been in Del Norte County, where in former days the 
Indians regularly fired the woods to make better feed for the deer, 
and the packers set fires to keep the trails open. Kidge after ridge 
has been wholly or partly reduced to a low chaparral growth, although 
there is evidence that a dense forest existed at a comparatively recent 
date. A conservative estimate of the loss of tanbark by fire within 
15 years in this region is 60,000 cords. 

In the second-growth districts the accumulation of debris inside 
the circles of poles about the remains of the parent stumps furnishes 
material for flames. Forty per cent of such poles show serious injury 
at the bases. 

("^TANNIN EXTRACT PROCESSES. 

.The difficulty of transportation has prevented the exploitation of 
some of the most productive tanbark oak regions in Humboldt and, 
to a smaller extent, in Mendocino County. An attempt was made 
to reduce this difficulty by grinding up the bark and shipping it in 
sacks, but this did not help in the more remote districts where the 
weight was the chief drawback. In the last few years attempts 
have been made to solve this difficulty by extracting the tannin 
from the bark and shipping the extract. 

Two methods have been tried in California, the open-pan process 
and the vacuum-pan process. The open-pan process was tried in 
southern Mendocino County hi 1900 and 1902, but was abandoned 
because the heat necessary to secure rapid evaporation in concen- 
trating the mixture of ground bark and liquid was said to scorch 
the fluid and start fermentation, so that the barrels containing the 
completed product often burst. 

The vacuum-pan process is used by an extract plant at Briceland, 
Humboldt County. The liquid from the leaching vats is pumped 
into settling tanks in the concentrator house, and thence fed as 
needed into the "pan" or evaporator, which is a copper retort about 
7 feet in diameter, heated by steam pipes coiled around the base. 
By heating the pan under vacuum the temperature of the liquid 
during evaporation is kept from exceeding* about 120 or 130 F. 



TANNIN EXTRACT PROCESSES. 21 

The vapor is condensed in a receptacle high enough above the pan 
to permit a 34-foot vertical waste pipe. This pipe, kept full of water, 
supplies a water column sufficient to offset the atmospheric pressure 
and maintain the vacuum. 

A cord of dry bark, 2,200 pounds, is reduced to 50 gallons of 
extract, which weighs about 550 pounds. The extractor has a 
capacity of 12 cords a day. 

SUPPLEMENTAL MATERIALS. 

The duration of the bark supply from tanbark oak will be extended 
somewhat by the use of other materials as supplements or substi- 
tutes. The superiority of the product of the tanbark oak over all 
other Pacific coast barks is due not altogether to its high percentage 
of tannin, but rather to the quality of the particular tannin con- 
tained in it, and perhaps also to the presence of certain other acids, 
such as gallic and acetic. The value of this combination is proved 
by tanning experience. Mixing imported tanning materials, such 
as gambier and quebracho, increases its effectiveness and counter- 
acts some of its undesirable qualities. As tanners have learned the 
use and value of these supplementary agents, methods have been 
more and more adapted to them, until to-day they are regarded as 
indispensable and the tanbark oak product is never used alone. 

As the accessible supply of tanbark oak grows scarcer and dearer, 
the bark from other species of oak is occasionally mixed with the 
superior material. This is especially the case in the southern dis- 
tricts, where the tanbark oak is more nearly exhausted. The barks of 
the California black oak and the coast live oak run so high in tannin 
that if tannin content alone were an index of tannage value they 
could compete with tanbark oak. They can not be used alone, 
because they will not produce leather of goo'd quality; the live-oak 
bark in particular imparts a gritty character to the leather, which 
ruins the knives of the cutters, but mixed in moderate quantities 
with the better bark they make possible a considerable saving. 

Alder bark is occasionally found in shipments of bark from tan- 
bark oak, but the tree does not grow in sufficient quantity in Cali- 
fornia to be a factor in bark supply. In the Mendocino woods the 
chinquapin is often peeled, but it contains so little tannin that it is 
practically worthless. Moreover, it is very fibrous and tough, which 
makes it difficult for the smaller tanbark mills to handle. 

Analyses of average bark samples from the main trunks of the 
important California trees are given in Table 10. Some of these 
have never been subjected to commercial experiment. 



22 CALIFORNIA TANBARK OAK. 

TABLE 10. Tannin analyses of bark of the more important forest trees of the Pacific coast. 



Species. 


Locality. 


Soluble solids. 


Insoluble 
solids, 
reds. 


Total 
solids. 


Tannin. 


Xontan- 
nin. 


Total. 


California black oak (Quer- 
cus calif or nica). 
California black oak 


Vaca Mountains, So- 
lano County. 
Briceland, Humboldt 
County. 
Berkeley 


Per cent. 
10.00 

10.16 
18.76 
7.92 

6.67 

12.18 

6.56 
11.97 
7.07 
6.20 
7.60 

8.60 
1.45 

15.58 
14.11 
13.45 

9.03 
17.52 

7.15 

10.80 
14.40 
2.50 

1.76 
3.91 


Per cent. 
10.25 

7.88 
9.40 
5.88 

2.83 
10.18 

5.19 
11.28 
4.93 
4.16 
4.34 

12.00 
3.09 

10.46 
2.85 
3.99 

4.59 
6.24 

5.25 
3.46 
6.56 
2.74 

5.72 
5.85 


Per cent. 
20.25 

18.04 
28.16 
13.80 

9.50 
22.36 

11.66 
23.25 
12.00 
10.36 
11.94 

20.60 
4.54 

26.04 
16.96 
17.44 

13.62 
23.76 

12.40 
14.26 
20.96 
5.24 

6.48 
7.76 


Per cent. 
0.95 

.32 
1.48 
1.20 

1.64 
.80 

1.00 
1.55 
.36 
1.00 
.64 

1.68 
.00 

.97 
2.60 
3.72 

.74 
1.60 

.42 
1.32 
2.42 
.10 

.59 
1.58 


Per cent. 
21.20 

18.36 
29.64 
15.00 

11.14 
23.16 

12.66 
24.80 
12.36 
11.30 

12. 08 

22. 28 
4.54 

27. Gl 
19. 50 
21. 16 

1^.36 
25. 36 

12. 82 
15.58 
23.38 
5.34 

7.07 
9.34 


California live oak (Quercus 
agrifolia). 
Highland oak (Quercus wis- 
lizeni). 
Highland oak 


Vaca Mountains, So- 
lano County. 
Southern Mendocino. . 
Vaca Mountains, So- 
lano County. 
South central Mendo- 
cino. 
Visalia 


Canyon live oak, maul oak 
(Quercus chrysolepis). 
Canyon live oak 

California white oak (Quer- 
cus lobata). 
Pacific post oak (Quercus 
garryana). 
Pacific post oak 


Southern Humboldt . . 

South central Mendo- 
cino, "Bald Hills." 
Southern Humboldt . . 

Mendocino coast . 


Western chinquapin (Cast- 
anopsis chrysophylla). 
Red alder (Alnu-s oregona)... 
California yellow willow; 
western black willow 
(Salix lasiandra). 
California laurel ( Umbel- 
lularia californica). 
Monterey pine (Pinus radi- 
ata). 
California swamp pine 
(Pinus muricata). 
Lowland fir (Abies grandis) 


Berkeley 


Briceland 


Berkeley (cult.) 


Mendocino coast 


...do 


Sitka spruce (Picea sitchen- 
sis). 
Douglas fir (Pseudotsuga 
taiifolia). 
Western hemlock ( Tsuga 
heterophylla). 
Western hemlock 


do 


Southern Humboldt . . 
Mendocino coast 

Noyo River, Mendo- 
cino coast. 
Mendocino coast 

do 


Redwood (Sequoia semper- 
virens) bark. 
Redwood, sapwood 


Redwood, heartwood 


do 







POSSIBILITIES OF UTILIZING THE WOOD. 

The tanbark oak peeled since 1850 is equal to more than 2,000,000 
cords of firewood. But, chiefly on account of the difficulty of trans- 
portation, little of this amount, perhaps 5 per cent, has been used as 
fuel. Yet the wood has such particular value for special purposes 
that it is quoted in San Francisco at from $12 to $18 per cord, a price 
much higher than that of any other California oak. The wood burns 
up very completely with little smoke. The United States mint 
at San Francisco uses it, and there is a steady demand by the bakers 
of that city. The full possibilities of the wood for lumber can be deter- 
mined only by experiments in sawing and seasoning and by strength 
tests, but its availability for some purposes is undoubted. About 
400,000,000 feet have been utterly lost so far, and about 627,000,000 
feet are still standing. To utilize the log for lumber, it must be cared 
for immediately after peeling. Only the redwood logging companies 
possess facilities for yarding and sawing the tanbark oak; yet since the 
peeling time comes at the height of their busy season, any proposal 



CONCLUSIONS. 23 

to depart from the custom of abandoning the tanbark oak log as use- 
less does not meet with favor. Moreover, their milling machinery 
is not well adapted to sawing oak logs, and, for satisfactory work, 
the installation of special plants would be necessary. 

Country wagon makers in the Coast Range constantly use tanbark 
oak for repair work and believe it superior to all other wood for felloes. 

The wood, unlike some others, such as the eastern chestnut, has no 
value whatever as a tanning agent. 

CONCLUSIONS. 

(1) The bark of tanbark oak is one of the most valuable tanning 
agents known for the production of heavy leather. Bark from the 
interior ridges and southern districts is prized more than bark from 
the deep redwood belt or from northern districts, because it averages 
higher in tannin. 

(2) The Pacific coast tanbark-oak belt contains enough standing 
tanbark at the present time to supply the needs of California tanneries 
at their present rate of consumption for 47 years. 

(3) There should be more systematic methods in peeling and a 
greater proportion of the bark above the clear trunk should be taken. 
Bark from one-half to one-fourth inch thick ^should be saved when- 
ever possible. Chipped bark should be sacked before bunching the 
coil bark. Trees with bound bark should be temporarily passed, 
and not mutilated or sacrificed. Tops should be burned in the win- 
ter following cutting to prevent the destruction of young growth and 
of passed trees by wild forest fires. 

(4) Tanbark oak is surpassed in reproductive powers by no 
other forest trees in western America, except the redwood, and it 
stands very close to that species. A crop of sprouts will normally 
arise from the base of every peeled stump. In order to favor this 
crop, peelers should ring the trunk at base and not break the coil 
down below the surface of the ground. These sprouts will give rise 
to " second-growth" poles which are commercailly profitable to peel 
within 25 or 35 years. 

(5) Standing trees after being peeled may live on indefinitely, but 
they never produce a second bark which has any commercial value. 

(6) The wood is, for the most part, allowed to rot on the ground. 
Prompt care would tend to obviate its greatest weakness, checking 
in seasoning, and it can certainly be applied to some of the uses for 
which oak wood is prized, and a stupendous annual waste thereby be 
eliminated. 

(7) Forest fires are a source of great annual loss, and. cooperative 
measures should be taken by the State of California, the coast counties, 
the redwood companies, the tanbark companies, and cattle-range 
owners to reduce the danger from fire. A conservative treatment 
of the redwoods to obtain a continuous crop will be of like advantage 
to the tanbark oak mixed with it. 



PART II. UTILIZATION OF THE WOOD OF TANBARK OAK, 

By H. S. BETTS. 
TANBARK-OAK LUMBER, v 

While the wood of tanbark oak is sometimes used for fuel, it is 
more generally burned in the redwood logging operations, or left to 
rot in the woods. The object of this study is to bring to the atten- 
tion of west coast hardwood users and the owners of tanbark-oak 
stumpage the possibility of using tanbark-oak lumber. 

The largest part of the hardwoods used on the Pacific coast is 
imported from the eastern part of the United States. From 1899 to 
1906 there was an increase in the price of hardwoods in the East of 
from 25 to 65 per cent. These conditions have been reflected in the 
western hardwood markets. Not only are the prices of most kinds 
of hardwood going up rapidly, but in some cases certain species are 
difficult to obtain at any price. This scarcity is due not to any local 
condition, but to the general shortage of hardwood timber. The 
high price is due to the eastern market price, to which must be added 
about 85 cents per hundredweight in freight charges, or an advance 
of from $24 to $36 or even $40 per thousand board feet. 

Yet tanbark oak furnishes a fair quantity of good material. For 
instance,, the average yield of bark is from 1J to 2^ cords per acre. 
If, as seems reasonable, there are 800 feet board measure of lumber 
for every cord of bark, the yield in lumber would be from 1,000 to 
1,760 feet board measure per acre. Exceptionally fine stands yield 
as high as 8 cords of bark to the acre, which would mean 6,400 board 
feet of lumber. 

APPEARANCE AND CHARACTERISTICS OF THE WOOD. 

The wood of tanbark oak, like that of other oaks, is porous and 
has the characteristic strongly marked medullary rays. In color it 
is light brown, faintly tinged with red. When the wood is first cut 
the sap wood is somewhat lighter in color than the heartwood, but 
after a few weeks' exposure to the air the two become very similar 
in appearance. 

Exact knowledge of the rate of growth of tanbark oak is very 
limited. Seven forest-grown trees near Sherwood, Cal., showed varia- 
tions of from 10 to 20 rings per inch. The trees were from 14 to 27 
inches in diameter 2 feet above the ground. Even on the stump the 
24 



Bui. 75, Forest Service, U. S. Dept. of Agriculture. 



PLATE VI. 




FIG. 1. MACHINE AND METHOD USED FOR TESTING SMALL BEAMS. 




FIG. 2. SEASONING CHECKS IN THE BUTT OF A TANBARK OAK LOG THAT HAS BEEN 
SUBJECTED TO THE SEVERE TEST OF BEING TURNED UP AND EXPOSED TO THE HOT 
CALIFORNIA SUN FOR Six WEEKS. 



Bui. 75, Forest Service, U. S. Dept. of Agriculture. 



PLATE VII. 




FIG. 1. TANBARK OAK LUMBER FOR CAR CONSTRUCTION. 




FIG. 2. TANBARK OAK BOARDS AIR DRYING. 



APPEARANCE AND CHARACTERISTICS. 



25 



annual rings are difficult to distinguish, since the temperature changes 
from season to season are not marked enough to form the distinct 
bands of spring and summer wood common in eastern oaks. In the 
case of the lumber, it becomes impracticable to attempt to obtain the 
rate of growth of different pieces. 

STRENGTH. 

The material used in the tanbark oak tests was divided into three 
classes or shipments, differing in the age of the trees and the season 
of cutting. The first two shipments were selected in the summer 
during the peeling season, and represented in the first shipment the 
larger and more mature trees of the stand, and in the second shipment 
the smaller and younger trees. The third shipment was felled in 
October and represented the same wood as that obtained in the first 
shipment, but felled in the season when the bark was tight, or when 
the sap was not running. 

The strength of the wood in several conditions of seasoning is 
shown in Table 11. The three shipments had practically the same 
strength and, therefore, were combined in the table. 

TABLE 11. Strength of small clear pieces of tanbark oak, green, air-dry, and kiln-dry, 

size 2 by 2 inches in section. 

GREEN. 






Bending. 


Num- 
ber of 
tests. 


Mois- 
ture 
con- 
tent. 


Weight per 
cubic foot. 


Fiber 
stress at 
elastic 
limit 
per 
square 
inch. 


Modu- 
lus of 
rupture 
per 
square 
inch. 


Modu- 
lus of 
elastic- 
ity per 
square 
inch. 


Elastic 
resil- 
ience 
per 
cubic 
inch. 


As 
tested. 


Oven 
dry. i 


Average 


256 
26 
26 


Per ct. 

89.5 
110.5 
65.5 


Pounds. 
66.5 
71.7 
60.3 


Pounds. 
43.1 
48.1 
38.2 


Pounds. 
6,576 

8,283 
4,869 


Pounds. 
10, 707 
12,880 
8,632 


1,000 
pounds. 
1,678 
2,251 
1,203 


Inch 
pounds. 
1.49 
2.35 
.83 


High 10 per cent 


Low 10 per cent 



AIR-DRY (10 TO 20 PER CENT MOISTURE). 



Average 


567 


14.0 


45.2 


43.2 


9,080 


15, 512 


2,083 


2.27 


High 10 per cent 


57 


17.4 


51.7 


50.5 


11,901 


20,342 


2,771 


3.45 


Low 10 per cent 


57 


10.5 


39.5 


37.1 


6,482 


11,625 


1,511 


1.19 





















KILN-DRY (5 TO 10 PER CENT MOISTURE). 



Average 


31 


9.6 


45.4 


43.9 


9,289 


17,693 


2,292 


2.17 


High 10 per cent 


3 


' 10.0 


50.2 


48.8 


12,287 


22, 417 


2,966 


3.41 


Low 10 per cent 


3 


8.8 


40.9 


39.5 


6,600 


13, 077 


1,642 


1.11 





















26 



CALIFORNIA TANBARK OAK. 



TABLE 11. Strength of small dear pieces of tanbark oak, green, air-dry, and kiln-dry, 
size 2 by 2 inches in section Continued. 



GREEN. 





Compression parallel to 
grain. 


Compression perpendic- 
ular to grain. 


Shearing. 


Num- 
ber of 
tests. 


Mois- 
ture 
con- 
tent. 


Crushing 
strength 
per 
square 
inch. 


Num- 
ber of 
tests. 


Mois- 
ture 
con- 
tent. 


Strength 
at elastic 
limit, per 
square 
inch. 


Num- 
ber of 
tests. 


Mois- 
ture 
con- 
tent. 


Strength 
parallel 
to grain 
per 
square 
" inch. 


Average 


237 
24 
24 


Per ct. 

86.8 
105.4 
64.8 


Pounds. 
4.845 
5,819 
3,711 


244 
24 
24 


Per ct. 
77.9 
95.3 
59.7 


Pounds. 
1,355 
1,964 
926 


221 
22 
22 


Per ct. 
83.1 
103.. 
56.1 


Pounds. 
1,414 
1,685 
1.075 


High 10 percent. . 


Low 10 per cent 





AIR-DRY (10 TO 20 PER CENT MOISTURE). 



Average 


406 


14.4 


8,172 


316 


13 4 


1 656 


204 


13 3 


1 %0 


High 10 per cent 


41 


17 7 


10 405 


32 


16 9 


2 343 


20 


16 9 


2 402 


Low 10 per cent 


41 


10.7 


6,265 


32 


10 5 


1 238 


20 


10 6 


1 585 























KILN-DRY (5 TO 10 PER CENT MOISTURE). 



Average * 


28 


9.4 


9,398 


26 


9 5 


1 818 


22 


9 


2 037 


High 10 per cent 


3 


10 


10 737 


3 


10 


2 293 


2 


10 


2 384 


Low 10 per cent. . 


3 


8.2 


8,047 


3 


8 4 


l'366 


2 


7 3 


1 669 























1 The values in this column are based on a shrinkage of 18 per cent volume. The fiber saturation point 
is taken as 30 per cent moisture. 

Clear, straight-grained specimens free from defects are needed in 
determining the strength of the wood itself. The results of tests 
made on this class material can also be used for comparison with 
similar tests on other kinds of wood. Pieces 2 by 2 inches in section 
have been found weh 1 suited to tests of this kind. For bending, 1 
they are cut about 30 inches long, and for compression parallel to 
the grain and compression perpendicular to the grain, from 6 to 10 
inches long. The blocks for shear parallel to the grain are cut with 
a projecting lip that is sheared off under test. In making a bending 
test the beam is supported at the ends and loaded at the middle. 
The supports for the beam are on the weighing platform of the test- 
ing machine, so that the load on the beam can be determined at any 
time during the test. This load is applied by a crosshead which 
can be forced down on the test specimen by means of heavy screws 
turned by a train of gears. The deflection or bending of the beam is 
measured by an apparatus (PL VIII, fig. 1 ) consisting of a light steel 
frame on which is mounted a movable pointer. In making a test, 
the frame is rested on two nails driven into the beam near the ends 
and the pointer attached to the center of the beam in such a way 



1 For a detailed description of methods used in the tests, see Forest Service Circular 38 (revised), Instruc- 
tions to Engineers of Timber Tests. 



APPEARANCE AND CHARACTERISTICS. 27 

that it moves over a graduated arc when the beam bends, and thus 
shows the amount of bending. 

The test is begun by loading the beam with about one-twentieth 
of the probable breaking load and noting the deflection. The load is 
then increased by a certain increment which is recorded with the cor- 
responding deflection, and the process continued until the beam breaks. 
The results of tests on beams of various sizes are reduced to a unit 
basis, so that direct comparisons as to strength and stiffness can be 
made between pieces of different sizes of the same or of different 
species of wood. 

In computing the results, the breaking strength is represented by 
11 modulus of rupture," the stiffness by " modulus of elasticity," the 
load the material will carry without taking a set by " fiber stress at 
the elastic limit," and the ability to withstand shock without taking 
a set by " elastic resilience." 

Tests in compression parallel with the grain are made by crushing 
the specimens endwise as they stand upright on the platform of the 
testing machine. In the case of compression perpendicular to the 
grain, the tests are made by placing a piece of metal 2 inches wide 
across the test specimen as it lies flat on the platform of the machine 
and pressing the piece of metal against the block of wood by means 
of the crosshead of the machine. This test is carried only slightly 
beyond the elastic limit of the wood under test, as loading beyond 
that point has at present no significance. The action is similar to 
that of a rail on a tie. 

In making a shearing test the block is clamped firmly in a frame 
with the lip projecting. The frame is placed on the platform of the 
machine and the lip sheared off by means of a sliding plate applied 
against the upper surface of the lip and parallel to the gram. 

Table 1 1 shows the oven-dry weight of tanbark oak to be about 
43.2 pounds per cubic foot. Air-dry tanbark oak, containing 15 per 
cent moisture, weighs about 50 pounds per cubic foot, or 4,160 
pounds per 1,000 board feet. This weight is about- the same as that 
of white oak and is somewhat higher than that of red oak. 

The average bending strength (modulus of rupture) of green tan- 
bark oak is 10,707 pounds per square inch, and the average crushing 
strength, 4,845 pounds per square inch. The results of similar tests 
on several kinds of hickory by the Forest Service, including pignut, 
shagbark, mockernut, big shellbark, nutmeg, and water hickory 
show a bending strength of from 9,200 pounds per square inch for 
green nutmeg hickory to 11,450 pounds per square inch for green 
pignut hickory. The average oven-dry weight of pignut hickory is 
about 51 pounds per cubic foot. 

Such tests as have been made on eastern white and red oaks indi- 
cate that tanbark oak in bending and crushing strength ranks about 
the same as white oak and is somewhat superior to red oak. 



28 CALIFORNIA TANBARK OAK. 

Data are not available for a comparison of the toughness and stiff- 
ness of tanbark oak and the eastern oaks and hickories. 

Table 11 shows a considerable increase in the strength values of 
the air-dry material over the green, and a still further increase in 
these values for the kiln-dry material. 

In compression perpendicular to the grain, green tanbark oak has 
an average strength at the elastic limit of 1,355 pounds per square 
inch. Green Douglas fir has an average strength of 651 pounds per 
square inch. 

In shearing strength air-dry tanbark oak shows an average of 
1,960 pounds per square inch. Douglas fir has an average shearing 
strength of 770 pounds per square inch for air-dry pieces. 

Douglas fir would, of course, be expected to have lower strength 
values than a hardwood like tanbark oak. The comparison is used 
because such tests on other hardwoods have not yet been made. 

SEASONING. 

A number of the logs selected for testing purposes were sawed into 
boards for a seasoning test. Fifty 1-inch boards were put through a 
commercial dry kiln of the moist-air type in San Francisco. The 
results, while encouraging as regards the behavior of tanbark-oak 
lumber in a moist-air kiln, were not satisfactory, owing to the imperfect 
regulation of the kiln and consequent daily variations in temperature 
and humidity. After 40 days in the kiln a classification of the lumber 
gave the following: 





Number. 


Per cent. 


Good boards 


28 


56 


Boards slightly warped 


12 


24 


Boards checked at ends ... . 


4 


8 


Boards badly checked 


6 


12 









The average temperature of the kiln was only 85 F. for the 40 
days, whereas it should have been at least 110 F. The loss in sea- 
soning eastern oak for vehicle stock is placed at about 10 per cent. 

The method of seasoning used by a lumber company which owns 
considerable tanbark-oak stumpage that it is preparing to put on the 
market in the form of flooring is as follows : The logs as soon as con- 
venient after they come in from the woods are cut into IJ-inch 
material. This is then carefully piled in the open yard, with sticks 
every 18 inches, and allowed to dry from 3 to 6 months. It is finally 
kiln dried from 30 to 40 days at a temperature not to exceed 110 
F., when the boards are ready to be made into flooring. The kiln used 
is of the blower type. The results obtained in drying tanbark oak by 
this method have been very satisfactory. It should be remembered 
that the trees in this case were cut during the peeling season (May to 



Bui. 75, Forest Service, U. S. Dept. of Agriculture. 



PLATE VIII, 




FIQ. 1. TANBARK OAK FLOORING, AND THE METHOD OF STORING AND SORTING IT. 




FIG. 2. TANBARK OAK FLOORING READY FOR SHIPMENT FROM THE MILL. 



Bui. 75, Forest Service, U. S. Dept. of Agriculture. 



PLATE IX. 




TRANSVERSE SECTION OF A 2-YEAR-OLD TWIG OF TANBARK OAK, SHOWING TANNIN 
(DARK STREAKS AND AREAS) IN THE PITH, PITH RAYS, AND BARK. MAGNIFIED 30 
DIAMETERS. 



Bui. 75, Forest Service, U. S. Dept. of Agriculture. 



PLATE X. 




FIG. 1 .TRANSVERSE SECTION OF A S-YEAR-OLD TWIG OF TANBARK OAK, SHOWING THE 
DISTRIBUTION OF TANNIN IN THE PITH AND PITH RAYS. MAGNIFIED 30 DIAMETERS. 




FIG. 2. LONGITUDINAL RADIAL SECTION OF A S-YEAR-OLD TWIG OF TANBARK 
OAK, SHOWING THE TANNIN IN THE PITH AND PITH RAY CELLS. MAGNIFIED 30 
DIAMETERS. 



OCT29 1914 

Division of Forestry- 
University of California 



SEASONING. 29 

October) . It is very probable that winter-cut lumber could be sea- 
soned with less loss of material. 

Some of the boards and planks sawed from the logs selected for 
testing were piled under shelter and seasoned for about two years, 
when they were in the same condition as regards warping and check- 
ing as is usually found in eastern oaks similarly handled. Some of 
the lumber showed a tendency to a "blue rot," apparently caused 
by too close piling, since this defect was remedied by a wider piling 
that gave more circulation of air. 

In the case of some 200 pieces for mechanical tests (2 by 2 by 30 
inches), cut from material seasoned under shelter for two years and 
then kiln dried, the pieces showed practically no checking. The 
sides of the pieces were slightly depressed in a few instances, but on 
the whole their condition was excellent. 

All things considered, the seasoning of tanbark oak seems to offer 
little, if any, more difficulty than is experienced with eastern oaks. 

SHRINKAGE. ^) 

In order to determine the amount of shrinkage in tanbark oak, 
62 pieces (2 by 2 by 10 inches) were dried out slowly from a green 
to an oven-dry condition. The pieces were selected so that two 
sides were tangential to the annual rings. They were weighed and 
measured at intervals for a period of about one year. The drying 
was carried on first in a warm room and finally in an oven. 

When a piece of green or wet wood is dried, no change in dimen- 
sions takes place until a point called the fiber-saturation point 1 
(generally in the neighborhood of 30 per cent moisture) is passed. 
The wood then begins to shrink in cross-sectional area and continues 
to do so uniformly with the removal of moisture until it is bone dry. 
The longitudinal shrinkage is so small as to be negligible. Generally, 
the heaviest wood shrinks the most and sapwood shrinks more than 
heartwood of the same specific gravity. Shrinkage is greater in the 
circumferential than in the radial direction. 

The results of the shrinkage tests on tanbark oak showed an 
average shrinkage in volume of 18 per cent 2 when the pieces were 
dried from a green to an oven-dry condition. Of this amount about 
6 per cent is radial shrinkage and about 12 per cent tangential. Air- 
dry wood generally contains about 15 per cent moisture, so that the 
shrinkage from the green to the air-dry state is only about half that 
from the green to the absolutely dry state. 

The average shrinkage in volume with red oak when dried from a 
green to an oven-dry state is about the same as with tanbark oak. 
Both woods vary considerably. 

1 For a full discussion of the fiber-saturation point, see Forest Service Circular 108, The Strength of Wood 
as Influenced by Moisture, by H. D. Tiemann. 

2 This figure is based on dry volume. 



30 CALIFORNIA TANBARK OAK. 

HARDWOODS USED ON THE COAST. 

The hardwoods at present used in the Pacific coast States come 
from many foreign markets, and only a very small proportion of 
them are local woods. From the Eastern States are imported oak, 
ash, hickory, maple, cherry, basswood, black walnut, tulip poplar, 
birch, and elm; from Honduras, mahogany; from Mexico, Mexican 
mahogany, prima vera, or jenizero; from Hawaii, koa; from Aus- 
tralia, iron bark (one of the eucalypts) and red bean; and from 
Japan, Siberian oak. 

The hardwoods from the Eastern States come for factory use in 
the rough or ' i club " form; for the vehicle industry as roughly finished 
parts, such as spokes, hubs, bent rims, and sawed felloes; and for 
cooperage as rough staves and heading. The rest are in the form of 
1-inch and 2-inch boards and 3 to 6 inch planks from 6 to 16 inches 
wide and from 10 to 30 feet long. A small proportion comes in the 
form of squared timbers up to 20 by 20 inches by 24 feet long. This 
is for special-order work. The Mexican, Australian, Hawaiian, and 
Japanese woods generally come in the shape of roughly hewn timbers, 
the sizes ranging from 14 by 14 inches up to 36 by 36 inches and from 
10 to 20 feet long. These rough timbers are sawed into veneer stock, 
boards, and planks, as wanted. 

Eastern oak makes up by far the largest amount of hardwood used 
in California, with hickory next, followed by maple, ash, and cotton- 
w'ood. 

Some of the hardwoods have a variety of uses, while others are con- 
fined to special lines. Of the eastern woods, ash, maple, hickory, 
elm, and birch are used chiefly for wagon stock, only a small part 
being used as lumber. Oak is largely used for cooperage, lumber, 
and wagon stock, in the order named. The term "lumber" includes 
boards, planks, and timbers. Oak lumber is imported for such uses 
as flooring, inside finish, furniture, cabinet work, bank, store, and 
office fixtures, paneling, wainscoting, picture molding, and doors. 
The black walnut, cherry, and tulip poplar from the East, the prima 
vera, poplar, and mahogany from Mexico, the koa from Hawaii, the 
red bean from Australia, and the Siberian oak from Japan also go 
very. largely into special lumber orders like the oak. Basswood is 
used in the upper parts of wagons and carriages and especially for 
work in pyrography. 

A California-grown eucalypt, the blue gum, has been made into 
insulator pins which have proved very satisfactory. It is also used 
quite extensively for cordwood, to some extent for piling, and is being 
tried in the form of veneer for furniture and interior finish. It is very 
probable that the use of blue gum in California will be considerably 
enlarged in the near future. The black cottonwood is used princi- 



SUGGESTED USES. 31 

pally for fruit baskets, and for this purpose is cut into veneer one- 
twentieth of an inch thick. Some is made also into wagon stock. 

The cost of all hardwoods is high. Ash and plain oak average $100 
per thousand board feet, while quartered oak and hickory average 
$125 per thousand. Iron bark brings about $105 per thousand, and 
Siberian oak about $80 per thousand. This includes the cost of 
transportation. 

SUGGESTED USES FOB TANBABK OAK. 

Up to the present time little has been known of the possibilities of 
tanbark oak. The feeling has been that the wood was subject to 
checking and warping to such a degree as to render its use impracti- 
cable. All hardwoods are more or less subject to these defects, and 
it is believed that the difficulties encountered in seasoning tanbark 
will prove no greater than those which have been overcome in some 
of the eastern hardwoods. In fact, the experiments made by the 
Forest Service, which it must be remembered were conducted under 
unfavorable conditions, showed that the wood can be seasoned in a 
dry kiln in such a manner that more than half of it will be satisfactory 
material and only 10 per cent badly checked. 

The lumber company mentioned as manufacturing tanbark oak 
flooring has had several experimental floors laid and in all cases they 
have proved satisfactory under hard usage. About 200,000 feet of 
flooring has been made up, and about 1,000,000 feet of lumber is in 
process of drying. In sawing this lumber the regular equipment of a 
redwood mill was used. Tanbark oak seems well suited for flooring. 
It has a pleasing grain and color and the necessary hardness. By 
using short pieces of the same length, say, from 9 to 18 inches, grooved 
and tongued on the ends, as well as on the sides, the material can be 
closely utilized. In laying a floor from such pieces a pleasing effect is 
obtained by having each strip of flooring break joints with the strips 
on each side and by alternating the light and dark pieces in each strip. 

It is quite probable that tanbark oak will prove suitable for tight 
cooperage. There seems to be a feeling at present that a contained 
liquid would be affected by the wood, but so far as is known the wood 
has not yet been given a fair trial. In regard to the tannin in the 
wood, there is said to be a higher percentage in the case of eastern 
white oak (1.32 per cent) l than in the case of tanbark oak (0.63 
per cent). Of course there may be other constituents that render 
tanbark oak unfit for use as a liquid container, but it is at least worthy 
of a trial. 

As an inside finish, tanbark oak has the beautiful figured grain of 
other oaks, and there is apparently no reason why it should not give 

i See Yearbook for 1902, U. S. Dept. of Agriculture, article entitled "Chemical Studies of Some Forest 
Products of Economic Importance." 



32 CALIFORNIA TANBARK OAK. 

satisfaction. This seems to be proved by a number of finished speci- 
mens of the wood now in the Forest Service offices in San Francisco. 

The mechanical properties of tanbark oak render it suitable for 
wagon and car stock. In bending and crushing strength it compares 
favorably with eastern oak and hickory, which have for so long been 
used in such construction. In drying it shrinks about the same 
amount as red oak. Tanbark-oak bolsters for logging trucks are in 
use and giving satisfaction. A number of strips of tanbark oak 1J 
inches thick, 4 inches wide, and 6 feet long were steamed and bent at 
a wagon factory in Oakland, Cal., with as good results as with white 
oak under similar treatment. 

Under present methods the price of bark f. o. b. track in the regions 
of production averages $15 per cord. The fuel wood from the trees 
that furnished this cord of bark would amount to about 2 cords, 
worth on an average $5 per cord delivered at the nearest railroad. 
Bark and cord wood together, then, would be worth $25. The 2 cords 
of fuel would amount to about 1,600 feet board measure. If half of 
this is suitable for boards, it is evident that with the present price of 
oak lumber the returns would be greater if the tree were cut into 
lumber rather than cordwood. 

In conclusion, there seems to be no good reason why tanbark oak 
should not take its place in the Pacific coast hardwood market for 
many if not all the purposes for which eastern hardwoods are now 
imported; and if this is true lumber companies owning tanbark-oak 
stump age could profitably take up the utilization of this wood as 
lumber. In California, particularly, where such large quantities of 
hardwood are imported at a high and constantly increasing cost, a 
native oak with both properties and appearance that compare favor- 
ably with eastern oaks ought not to be allowed to go to waste, but 
should at least be given a commercial trial. 



APPENDIX. 



DISTRIBUTION OF TANNIN IN TANBARK OAK. 



By C. D. MELL. * 

Tannin is found in most plants and almost exclusively in the living 
cells, though there are some in whose cells it is not found, such as 
European hackberry (Celtis australis Linn.), white mulberry (Morus 
alba Linn.), black elder (Sambucus canadensis Linn.), honey locust 
(Gleditsia triacanthos Linn.), black locust (Robinia pseudacacia 
Linn.), and laburnum (Cytisus laburnum Linn.). It is always in 
the form of a solution in the cells and not in the cell membrane, nor 
in its primary membrane. Tannin, chlorophyll, and starch are 
closely associated; tannin and chlorophyll together in collenchyma 
and phelloderm, and tannin and starch together in the same cells in 
pith rays. Tannin is most abundant in the elements outside the 
cambium, and in a few cases it is present sparingly in wood fibers. 

An investigation of the tannin contents of a number of trees shows 
that several of the elements of tanbark oak have tannin distributed 
through them, as shown in Table 12. Tannin is present in such of 
the structural elements of each wood as are indicated by the letter x. 
The small circle indicates that the tannin content in the element, so 
marked is very small, and of no importance in connection with 
commercial operations. 

TABLE 12. Elements of pith, wood, and bark of trees containing tannin. 



Quercus dcnsiflora Hook, and Am. (tan- 
bark oak) 

Alnus glutinosa (L.) Gaertn. (black alder). 

Betula papyri/era Marsh, (paper birch) 

Carpinus caroliniana Walt, (blue beech)... 

Corylus americana Walt, (hazel) 

Satix purpurea Linn, (purple willow) 

Platanus occidentalis Linn, (sycamore) 

Hamamelis virginiana Linn, (witch hazel). 
Acer platanoides Linn. (Norway maple) ... 

Rhus cotinuft Linn, (young fustic) 

Pyrus communis Linn, (pear) 

Eucalyptus cordata Labill . (gum ) 

Ribes rubrum Linn, (currant) 

Syringa vulgaris Linn, (lilac) 

Fraxinu* americana Linn, (white ash) 



Structural elements containing tannin. 



x 



\ 



x 



33 



34 CALIFORNIA TANBARK OAK. 

To determine correctly the distribution of tannin in plant tissue, 
it is best to fix the tannin content in such a manner that it becomes 
hard, compact, and easily recognizable under the microscope in 
transverse and longitudinal sections. Tannin hardens into a compact 
mass when treated with potassium bichromate and, in transmitted 
light, has an intense red-brown color. 

The ultimate twigs, obtained from growing trees, are cut length- 
wise through the pith and are allowed to dry for 12 hours in a room 
of ordinary temperature. Then they are soaked in a solution of 
potassium bichromate for a week before the sections are cut. The 
material must be treated before it is sectioned, otherwise the tannin 
content will be distributed by the knife into elements where it does 
not naturally occur. The color does not change when the sections 
are mounted in glycerin, so the sections may be preserved in this way 
for classroom or other demonstration work. The first 8 or 10 sec- 
tions should be discarded, because they will include the outer cells 
coated by tannin that oozed out when the twigs were first cut; and 
they are likely to be disappointing because they will not show the 
undisturbed tannin content. The cells in which tannin occurs will 
be filled with a compact red-brown mass (Pis. IX and X) ; or there 
may be only a few small red-brown globules, as in the pith ray cells 
of European alder (Alnus glutinosa, L. Medic.). 

An investigation of this sort shows that tannin is present in the 
twigs of tanbark oak as well as in the older bark, and that tanning 
extract could be made from the twigs and smaller branches, as in 
the case of the eastern chestnut (Castanea dentata). Yet there is 
but little tannin in the wood-parenchyma elements of the heartwood 
of tanbark oak, so that tanning-extract can not be got by chipping 
the wood and subjecting it to tanning-extract processes, as in the case 
of the chestnut. 

o 



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