t-'urchased by the Fore £
Service for official use
APRIL, 1955
FOREST ENTRANCE. This 60-year-old stand of Douglas fir has been thinned twice in a
program of. light, frequent thinnings. Salvage logging recovers sixty-two percent of the road costs.
·
Mortality -Can Be Salvaged
By NORMAN P. WORTHINGTON
HOW MUCH MORTALITY occurs
in young starids of Douglas•fir? What
effect does thinning have on mortal­
.ity? C3,n forest owners afford to
salvage mortality in their y o. u n g
stands?
These are live questions throughout
Pacific Northwest Forest ·and Range Experi­
ment Station Forest Service, U. S, Dept. Agri.
the Puget Sound area, particularly
where intensive management is being
introduced. Studies on the McCleary
Experimental Forest are giving answers to such questions.
This Forest, located in northeastet:n
Grays Harbor County, Wash., is a co­
operative research project by the
Simpson Logging Company and the
U. S. Forest Service. It is devoted
primarily. to a test of commercial
·
OPENI.NC IN STAND resulted from root rot.
Unthinned stand had annual mortality loss
of 418 board feet per acre, as a·gainst 115
board feet pe_r acre for the thinned stand.
·
thinning practices in site II 45- and
60-year-old D_ouglas-fir with varying
mixtures of alder and cedar. A 200­
acre section of the forest has been
covered by five annual thinnings of
approximately 40 acres each during
the period 1949-53. As part of this
study, information on mortality has
been compiled from recent measure­
ments. Thinnings have removed 13
to 15 percent of the total cubic vol­
ume.
MORTALITY: THINNED AND
UNTHINNED STANDS
WEAK ROOT system on shallow soil caused this windfall in the thinned area. Annual loss from
windthrow was 86 board feet per acre on thinned stand, opposed to 169 bd. ft. on unthinned.
Growth . and mortality data are
based on analysis of 5-year records
from twenty-one 1/5-acre plots in a
40-acre tract thinned in 1949 and
eight 1/5-acre plots on an adjoining
unthinned area of 18 acres.· Gross in­
crement, including mortality, was ap­
proximately the same for the thinned
and unthi.nned plots (Table 1). The
small difference in favor of the thinned
area may be attributed to chance.
However, it is significant that incre­
ment on the thinned sta11d has not
been depressed by cutting.
Table 2
Volume of annual mortality by cause (acre basis), 1949-1953
Table I
<iross annual increment (acre basis), 1949-1953
Board Feet
Cubic Feet
Cause International
Thinned I Unthinned
Thinned I Unthinned
Wind throw
Suppression
Root rot
Logging injury
Unknown
Treatment
Thinned
167
1,097
949
Unthlnned .
145
1,097
900
lTrees 5.6 inches d.b.h. and larger to 4-ln. top.
•International rule, %-inch kerf, for trees 7.6
inches d.b.h. and larger to 6-lnch top; Scribner
rule for trees 11.6 inches d.b.h. and larger to
an 8-inch top.
Totals
. Apparently the 1949- thinning fore­
stalled or "pre-salvaged" much mor­
. tality that normally would have oc­
curred in the ensuing 5 years. this
effect is particularly apparent in com­
paring .losses due to suppression. Prac­
tically no trees died from suppression
where the stand had been opened by
thinning. In the unthinned stand, sup-.
pression was a rriajor cause; wind­
throw another. In the thinned stand,
windthrow and root rot (Poria weirii)
were the chief offend(lrs. Logging in­
jury caused a high proportion.of cubic
foot and International volume losses,
but was not important in the Scribner
board foot measure since most trees
damaged were less than 10 inches
d.b.h. Loss from root rot was prob­
ably underestimated on both areas. It
is likely that much mortality recorded
as windthrow or · unknown" was really
caused by root rot.
Reduction of mortality is a major
justification for thinning. When mor­
tality is held to a minimum there is
a signifimint increase in net increment:
·
Thinned
Unt·hinned
- Scribner bd. ft, 949
900
115
418.
834
. 482
Acre basis
Gross Increment
Mortality
Net increment
Mortality compared to
gross increment (%)
12
The magnitude of these differ
46
ces
is possibly exaggerated due to sam­
pling error and lack of complete uni­
formity of the two areas, but the prin­
ciple and trend are valid.
.
.
.
SALVAGING MORTALITY
There is a substantial amount of
mortality worth salvaging in both
thinned and unthinned stands. On the
McCleary Experimental Forest, mor­
tality is systematically salvaged every
two years to minimize deterioration of
19
6
7
14
1
32
43
9
0
20
118
8
33
33
0
218
257
61
0
118
86
0
20
9
0
169
148
46
0
55
47
104
192
654
115
418
115 bd. ft. Scribner
at $9.17 per M . . . . . . . . . . 1.05
(average 4-yeai: stumpage
price less 25 percent reduc- ­
tion for increased yarding
cost)
Net cost per acre . . . :. . . 63
the dead trees. This has been pos­
sible- on the thinned area because an
adeguate road system makes light and
frequent salvage cuts .. practicable.
Thinning forestalls much mortality; in
addition, most of that which did
occur was salvaged in the thinning
operation and put to productive use.
Less complete salvage was obtained
on the check area (purposely reserved
from treatment) because the road sys­
tem does not reach this· area.
The sample plot showed that mor­
tality was a serious drain on the un­
thinned area (Table 2). During the
5-year period 418 board feet Scribner
per acre died. annually, which is 3.6
times the mortality .on the thinned
area. Measured in cubic feet, losses
were 2.2 times. as great on the un­
thinned as on the thinned, in Inter­
national 3.4 times. Even mortality on
the thinned area (115 board feet per
acre Scribner) is more than the total
net increment in many commercial
forest types in the United States.
·
__
·
.
Effect of salvage on net increment
·
D ring the five years (1949 to 1953)
in which salvage on the 200 acres in
the thinning experiment has been
carried on, dose record was kept of
all salvaged mortality removed dur­
ing logging operations. The result has
been impressive:
Unthinned
Thinned
- Scribner bd, ft'. 482
. 834
Net increment
169
115
Salvaged mortality
938
651.
Revised net increment
Increment Increase due
35
14
to salvage (%)
Acre basis
'·
Scribner
Thinned I Unthinned
This experience illustrates that mor­
tality. need not be a cpmplete loss in
a managed forest; a considerable por­
tion is usable and can make· a sub­
stantial contribution to net increment.
Economics of salvage
Normal mortality has financial
significance. It should not be ignored
or underestimated. . Approximately
115,000 board feet, Scribner, has been
salvaged from 200 acres thinned in
the past 5 years, or 115 board feet per
acre annually. Thi does not inelude
salvage from check areas.
In order to make thinnings, which
reduce mortality, or to salvage it when
it does occur; an adequate road. sys­:
tem is essentiaL At McCleary 1.95
miles of road serve 340 acres-a rate
of 1 mile of road to 174 acres. Costs
have averaged $4,831 per mile for a.
graded· imd surfaced road adequate
for light annual cuts. This is $27.76
per· acre. Financial aspects of the
problem may be analyzed as follows:
Annual road construction and mainte­
nance costs per acre:
Interest on construction
cost ($27.7 6 x 4%) . . . . . . .$1.11
Maintenance ($100 per
mile/174 acres) . . . . . . . . . .57
$1.68
Annual value of mortality salvage:
.
Road costs of $1. 68 per acre per year
are partly offset by stumpage return
of $1.05 froni salvage, leaving a net
out-of-pocket expenditure for roads
of only $0. 63. Thus, returns from
salvaged mortality alone are paying for
62 percent of road construction and
maintenance.
In addition to making possible
thinning and salvage, a road system has other advantages: it aids fire pro­
tection and reduces costs in final cut ting. All uses bear a share of road costs, but these costs ,are offset by
increased forest revenue-revenue that would be lost if roads were not built. This McCleary example simply isolates a single use of a road system and shows how mortality salvage alone
(over and above that forestalled by
thinning) justifies a large share of the
total expenditure. Had no thinning
been done, mortality would have been
much heavier, probably approximating
the 418 board feet per acre per year
recorded on the unthinned study area
plots. In our example, 184 board feet
per acre salvaged would completely
pay road construction and mainte­
nance costs.
CONCLUSION
This example of mortality in a man­
aged forest, showing cau,se, effect on increment and financial returns, in­
cluding road development costs, is based on actual experience op. Mc­
Forest.
Cleary Experimental
All
logging and road building have been
done on a. commercial basis by an
Data are
independent contractor.
·actual measurements and do not repre­
sent exceptional circimistances. Com­
parable results could be expected on
similar stands elsewhere in the Puget
Sound marketing area. However, the
principles are applicable regardless of
specific
location.
Forest
owners
should reconsider mortality in their
timber and see if a new look at its
salvage is not financially justified.
·
• Willamette Fibre & Chip Board,
Inc. has recentlv made test runs of its
chipboard panel. TPst run were tem­
porarily interrnpted hy a fire in Feb­
ruary in the drier and drier house.
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FOR SAWTIMBER
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Over 16.511
TWELVE YEARS af­
ter first t h i n n i n g
(when picture was taken) 50-y e a r - o l d stand had about 91 cords per acre, was
ready for a second .
thinning. A p p r o x i-· mately 25 cords per
acre were removed in first thinning, 15 in the second. TREE SIZES - DIAMETER BREAST HIGH
TWELVE YEARS after thinning and pruning, growing stock in the 50-year-old thinned stand was concentrated in clean-boled ' mer­
chantable trees, 12 to 16 inches diameter. In the unthinned stand great portio was in trees below merchantable size or large trees, rough and hmby. Volume .
m two stands was about same despite removal of 3,460 bd. ft. per acre from ,thinned stand. Trees that survived were, without ex­
. ception, large, dominant Douglas­
firs. Most trees died because their
crowns were consumed by the fire, al­
though some that survived died later from attacks by insects and disease. ·
Thinning Trials Have Requiem
By GEORGE R. STAEBLER
The Kugel Creek plots on the Olym­
pic National Forest, Wash., represent
one of the earliest thinnings of Doug­
las-fir in the Pacific Northwest. They were destroyed September 20 1951
in the Port Angeles and Wester Rail­
road fire. Loss of the plots is an un­
fortunate setback to advancement of forest management knowledge. Al­
though much useful information may
be found in the 17-year record prior to the fire, the plots would have pro­
vided increasingly valuable data in
the years to come.
The herculean task of salvage after
this spectacular 35,000-acre fire on
the north side of the Olympic Penin­
sula has been widely publicized, as
has been the huge job of reforesting
the denuded mountain slopes.
Less publicized, but none the less
costly, was the loss to forestry of the
sample plots in the 50-year-old Kugel
Creek stan
. d near Snider Ranger sta­
tion. About 10 acres of this stand had
been thinned and pruned in 1937 by
the Civilian Conservation Corps. The
.stand was then 38 years old. This
project of the Olympic National For­
est was under the supervision of .staff­
m n Ed Hanzlik and Sandy ' Floe,
.
D1stnct Ranger at Snider.
Fo:ur sample plots, covering 3%
acres, were established by the PacifiC!
Northwest Forest and Range Experi­
ment Station. All trees were tagged
and careful, individual tree measure
ments have been kept. Three plots
were thinned and one was left in its
natural state for comparison. Three
years before the fire the stand was
thinned again, but because of the fire,
·
·
'
Pacific Northwest Forest and Range Experi­
ment Station, Forest Service, U. S, Dept. Agri.
ON THINNED PLOTS damaged was
far less severe than on the unthinned
plot. Only 37 percent of the total
cubic-foot volume of the thinned
stand was killed by the fire, whereas
on the plot that had never been
thinned, 7 6 percent of the volume was lost. Even merchantable trees, 12 or
more inches in diameter, suffered more heavily on the unthinned check plot, where 74 percent of the board foot volume was destroyed. On the thinned plots, about the same pro­
portion survived. In the 1937 operation by the CCC; all small trees were removed and
enough larger ones to make openings
between the crowns of remaining
trees. Most of the trees left were
pruned up to 20 or 34 feet. Crowns
were further "loosened" by the sec­
ond thinning in 1949. When the fire
struck, there was a well-established
unde story of small, green cedar and
little is known regarding the effect of
this second operation.
NOT UNTIL AFTER World War II
did thinnings like those at Kugel Creek
become commercially feasible. With­
out these earlier. efforts it would have
been necessary to tackle the recent
operations "blind"-with little idea of
what results to expect. Such knowl­
edge is gained only by the Kugel
Creek type of field trial, and long-time,
painstaking observation and analysis
of data. The loss of future results,
however, does not detract from the
results obtained to date, and the 12year record after the original thinning
(17 years including the fire that spelled
the plot's demise) does provide highly
useful information.
The records demonstrate:
(1) Fire damage in thinned and
pruned stands is far less serious than
in unthinned stands.
(2) At least 25 cords per acre may
be cut from a 38-year-old Douglas-fir
forest without reducing the growth of
the stand. In fact, growth in board
feet is substantially increased.
(3) After thinning, growth is con­
centrated on the best trees.
The fire in the Kugel Creek stand
was so hot that numbered aluminum
tags nailed to trees were completely
oxidized, leaving a fragile paper-thin
"ash" hangin
to the nails. Tree
trunks were blackened many feet high.
·
·
ALTHOUGH ALL trunks in thinned stand
were fire blackened for many feet of their
length, fewer trees were killed by having_..__
crowns destroyed than in unthinned stand.
Three years after, the fire thinned stand still
had 22 thousand board feet per acre in live
tree, twice the live volume on the unthinned
plot. Photo taken six months after fire.
"
hemlock trees, but otherwise there
were no flashy fuels between the
ground and the live crowns of the
trees. By contrast, the unthinned
stand had an abundance of dry, highly
inflammable fuel-small standing dead
trees and dead limbs from the ground
up on live trees.
Also, the crown canopy was so
complete that fire· apparently spread
easily from crown to crown. These
factors all seemed to help account for
the great difference in damage be­
tween thinned and unthinned stands.
Although small trees, dead or alive,
are not cut in a normal commercial
thinning, many are destroyed· or
knocked down. Cutting the rest, or
most, of them would be excellent fire
insurance.
APPROXIMATELY 25 CORDS per
·
acre were cut by the CCC in 1937
when the stand was 38 years old. This
was the volume of trees 6 inches and
over in diameter to a 4-inch top. Al­
though 6- and 7-inch trees would not
be marketable for pulpwood in most
of the Northwest even today, it is a
common practiCe to utilize such trees
in the East and South. The board­
foot volume of the 1937 cut, however,
would be an economic harvest in most
places; in trees 12 inches d.b.h. and
over, th'e cut average 3,460 board
feet per acre, Scribner rule.
Twelve years later the thinned
stand had about the same board-foot
volume as the unthinned. It had grown
as much as the unthinned stand, and,
in addition, had nearly grown back
the volume removed in thinning.
Growth on the three plots was 1,393,
1,578, and 1, 614 board feet per acre
per year, averaging 1,554, against
1,305 for the untreated plot.
In terms of cords, again assuming
6-inch trees to be merchantable, the
thinned stand grew back the 25 cords
cut plus an additional 16 cords or
3.4 cords per acre annually. The
check plot also grew 3.4 cords an­
nually, but had yielded no return to
the landowner.
From this, it can be concluded that
a substantial amount of growing stock
may be removed in a careful thinning
of a fully-stocked 38-year-old stand
without reducing the growth rate. In
fact, board-foot ·production will be
speeded.
NOT
ONLY HAS the experiment
demonstrated that growth .er· thin­
ning is equal to, or more han, the
growth in unthinned stands, it also
showed that thinning produces a better
stand since the remaining trees,
though fewer in number, are larger
and of higher quality.
When the stand was 50 years old,
12 years after thinning, the unthinned
stand had 10,400 cubic feet per acre
in all trees-about ;11 more than the
thinned stand. However, only 6,060
cubic feet of this was in trees of saw­
timber size, 12 inches d.b.h. and over
-less than 4 percent more than the
5,830 cubic feet in the thinned stand
in the same sizes. Consequently, the·
two stands had about the same board­
foot volume in merchantable trees:
25,000 board feet in the thinned stand
to 2 6,500 board feet in the unthinned.
Furthermore, in the thinned stand
21,500 board feet was in the higher
quality 12-, 14-, and 1 6-hioh trees.
On the check plot only 17,000 board
feet was in these sizes, the remaining
9,500 being in rough, limpy, large
trees of the type that was cut in the
thinned stand because of poor quality.
This conce.ntration of the growth
capacity of the site on trees of the
forester's choice is a most beneficial
effect of thinning, and is abundantly
demonstrated by the Kugel Creek
plots. Although repeated thinnings
and continued observation are re­
quired to learn more of the long-term
trends, the Kugel Creek record stands
out as very much more than a mere
indication of the benefits to be ex­
pected.
Reprinted from the April, 1955 issue of THE LUMBERMAN
The Production Journal of the Forest Industries