PRUNED DOUGLAS FIR young growth
provided the relatively clear veneer shown
at left. The distortion of grain is negligible
outside of the pruned knots.
UNPRUNED DOUGLAS
FIR
young
growth would produce the type of knotty
veneer at right. This panel was cut from
the inner portion of a pruned fir block.
Fact
or
Fancy?
Peelers From Pruned Douglas Fir
C
AN plywood face stock be recovered
from the clear wood grown on
young-growth Douglas fir trees
pruned at an early age? This question
might well be asked by any tree grower
who has an eye toward quality improve­
ment of his timber crop. If pruning pro­
duces peelable, knot-free wood, young­
growth logs can be sold as high-quality
peelers, substantially increasing their
value.
To explore this question, forest service
researchers pioneered a study during the
summer of 1955 to determine the quality
and appearance of veneer that might be
obtained from pruned logs. Their find­
ings-although not conclusive-indicate
that pruning Douglas fir at an early age
is a sound investment.
Heretofore, possibilities of veneer re­
covery from pruned Douglas fir young
growth had been confined largely to
theorizing. The main reason for this is
that few existing stands were pruned
long enough ago to show results. One of
the oldest examples of thinned and
pruned Douglas fir in the Pacific North­
west is a 56-year-old stand at Kugel
By EDWARD J. DIMOCK II
Pacific Northwest Forest and Range Experiment Station-Forest Service U, S. Department of Agriculture *
Creek on the Olympic National Forest.
This stand supplied the logs for the test
peeling.
Selected many years ago by the forest
service as a testing ground for applied
forest research, this stand has had a truly
remarkable and dramatic history. In 193 7,
when 38 years old, it was thinned and
pruned as a wintertime CCC project, and
four permanent sample plots were estab­
lished to observe subsequent growth and
reaction to thinning. With a second thin­
ning in 1949, the stand showed increas­
ing promise of becoming a good example
of intensive forest management. In addi­
tion, the aesthetic appeal of the cleanly
pruned boles was felt keenly by all ob­
servers.
Unfortunately, however ,the disastrous
Port Angeles and Western Railroad fire
in 1951 burned heavily over the area and
necessitated abandonment of the original
experiment. Interestingly enough, the
thinned and pruned sample plots sur­
vived the fire with far less damage than
the surrounding unthinned timber. Al­
though abandoned for experimental pur­
poses, the stand still conr:tins a number
of pruned trees that were merely scorched
and not killed in the conrhgration. It ap­
peared that selected trees might well pro­
vide sufficient data to illustrate the possi­
bilities of veneer reco,·er · from pruned
logs.
Accordingly, in July 1955, two sur­
viving trees with 18 years' growth since
pruning were selected for an exploratory
recovery analysis. One tree, which grew
6.6 inches at d. b. h. since 193 7, repre­
sented optimum growth on the area; the
other, which grew 4.4 inches over the
same period appeared to approximate
more nearly average growth. The six
blocks cut from the two trees ranged in
diameter from 14.6 to 16.6 inches inside
bark at the small end .wd had grown
four to five inches in diameter (inside
bark) since pruning. Growth counts av­
eraged seven to ten rings per inch.
Through the cooperation of the Geor-
EXPERIMENTAL BLOCKS: Side view at left shows 4-foot
veneer blocks cut from butt section of Douglas fir that had
been pruned to height of about 18 feet. End view of same
blocks, above. Dark rings show year in which the trees were
pruned. Outer shells of wood represent 18 years of growth since
that time. The outer portion produced knot-free veneer.
gia - Pacific Corporation in Olympia,
Wash,. arrangements were made to peel
the blocks and manufacture several dem­
onstration panels. Peeling was done on
the company's 4-foot lathe, which is used
normally to peel cores from the larger
10-foot lathe. The core lathe, which is
equipped with a solid pressure bar, was
set to cut core veneer with a thickness of
1/10-inch, a standard size. The lathe
chuck was centered in the pith of each
block in order to follow the rings as
closely as possible and produce the maxi­
mum amount of smooth-cut veneer. As
the blocks were peeled, it became increas­
ingly evident that the wood laid down
over the knots contained a minimum of
cross-graining or distortion and that clear­
faced veneer could be cut almost imme­
diately adjacent to the pruned-knot sur­
faces.
When all six blocks had been peeled
to approximately 5-inch cores, the recov­
ered green veneer was inspected to de­
termine its quality and general appear­
ance before drying. The best material was
relatively clear and contained only scat­
tered defects such as pin knots, splits,
torn grain, and occasional partially ob­
scured knots. (The pin knots were pre­
sumably from small internodal branches
not removed in pruning.) The remaining
veneer, cut nearer the centers of the study
blocks, contained a liberal variety of de­
fects, including a great number of both
tight and loose knots.
Selected Face Panels
Following drying, veneer from outer
shell areas and knotty core areas was edge­
glued separately to form sheets fully fifty
inches square. Then, several sheets of ve­
neer were selected from each group to
form the faces of demonstration panels
that would show the extreme variations
in appearance. Finally, the finished panels
of 3-ply If.!-inch construction were sanded
to show more clearly the desirable fea­
tures and less obvious defects.
Appearance of the dear-faced panels
was generally good. With patching the
faces could be considered potential grade
A under Douglas Fir Plywood Commer­
cial Standards. The knotty veneer, on the
other hand, would not grade higher than
C. A small amount of torn grain was
evident on the faces of all panels, par­
ticularly on those that had been derived
from the sapwood portions of the blocks.
Improved lathe facilities and peeling
practices would be expected to minimize
this defect.
Due to the pioneer nature of the study,
a detailed analysis of the actual peeling
operation was not attempted. However,
even without an exact determination of
production by grades, it was evident that
the proportion of high-grade material
was not high. Several factors contributed
to this. The practice of centering the lathe
chuck in the pith, rather than in the
geometric center of each block, resulted
in some loss due to eccentric bole shape.
There also was evidence of a certain de­
gree of carelessness in the original prun­
ing job. Failure to trim the branches
cleanly and as close to the bark as possible
may have had considerable bearing on the
relatively low recovery.
Outlook Promising
At the present time, this experiment
remains as a rough though unique attempt
to discover some of the factors that will
be met in peeling pruned young-growth
Douglas fir. The outlook for future util­
ization of pruned trees in the veneer and
plywood industries is indeed promising,
and more closely controlled studies of
this type are needed. A more comprehen­
siYe study, which will include a quantita­
tive determination of grade recovery, is
planned by the Pacific Northwest Forest
and Range Experiment Station and the
U. S. Forest Products laboratory.
It is highly significant that veneer ob­
tained immediately outside pruned knots
showed no appreciable distortion in wood
structure. It is also noteworthy that a
commercially acceptable quality of face
stock veneer was obtained from trees with
less than 20 years' growth after pruning.
The possibilities for producing peeler
logs under a normal rotation with several
times this growth after pruning make a
fascinating topic for speculation.
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Reprinted from
Leadin g Timber Industry Journal
PORTLAND, OREGON
Vol. LVII, No.9 July, 1956
PURCHASED
BY
THE FOREST SERVICE
FOR OFFICIAL USE