FOREST AND RANGE EXPERIMENT STATION
•
u.s.
DEPARTMENT OF AGRICULTURE. PORTLAND, OREGON
September 1966
PNW-43
LABOR REQUIREMENTS IN THINNING DOUGLAS-FIR
AND WESTERN HEMLOCK ON TWO EXPERIMENTAL FORESTS
IN WESTERN WASHINGTON
by Norman P.
Worthington
INTRODUCTION
Throughout the Douglas-fir subregion of western Oregon and west­
ern Washington, commercial thinnings of young-growth stands of Douglas­
fir and western hemlock are increasing. Both research findings and
operating experience have demonstrated increased stand productivity
and profit from the thinnings.
The Pacific Northwest Forest and Range Experiment Station has
been engaged in research over the past 20 years to discover some of
the silvicultural and economic factors which would influence thinning
practice. We have accumulated a series of time and production records
from several studies of thinning methods.
NATURE OF STUQIES
This paper analyzes and discusses data obtained during thinning
of young Douglas-fir and western hemlock in cen'tral western vashington
using three skidding methods. Information is presented on how total
labor requirements are affected by (1) volume thinned per acre and(2)
average d.b.h. of trees cut.
During the period 19 51 through 1965, records were obtained from
seven different operators in 25 thinning operations.l/ Eleven of
l/ Size of Douglas-fir areas ranged from 31 to 44 acres and
hemlock stands from 11 to 25 acres.
these were in 45- to 75-year-old site II Douglas-fir, with small
quantities of cedar and western hemlock and up to 20 percent of alder,
on the McCleary Experimental Forest near McCleary, Wash.l / Stand vol­
umes were 5,000 to 8,000 cubic feet per acre in trees averaging 20
inches d.b.h. The remaining 14 thinning operations were in pure 50­
to 60-year-old site II western hemlock on the Hemlock Experimental
Forest near Hoquiam, Wash. ,11 with stand volumes of 7,500 to 10, 000
cubic feet per acre in trees averaging 18 inches d.b.h.
DESCRIPTION OF THINNING METHODS
The most obvious difference in the methods was in the skidding
operation. Skidding was either by horse, crawler tractor, or a four­
wheel rubber-tired tractor known as a Tree Farmer. Other operations
were similar.
Trees were marked prior to cutting, and thinning was completed
primarily during June through October of each year. Crews varied from
one to five men, but generally were three: a tree feller, a horse
skinner or tractor operator and loader, and a truck driver. Truck
roads were already constructed before thinning began, at the rate of
1 mile for each 135 acres, and roadbuilding by contractors was not
required.
Contractors were local loggers experienced in thinning or partial
cutting. Generally they purchased the stumpage, based on individual
tree marking tallies. Logs and pulpwood were disposed in the best
market available to them. However, in about 20 percent of the cases,
the thinnings were by a contract piece rate, with delivery to a market
specified by the timber owner. All thinnings at McCleary were made
into saw or veneer logs, whereas at Hemlock, 8 0 percent went into
pulpwood. Trees were usually cut by powersaws into 12- to 20-foot
lengths but occasionally 8-foot or 32-foot lengths. Loading generally
was by a forklift hydraulic loader but occasionally with a portable
swing boom or self-loading truck. Hauling was by 2-1/ 2-ton truck alone,
or truck with either semi- or full trailer. In all instances, the
operations were similar to those currently in use in the area, except
that there was a tendency to use light equipment and small crews. The
only unusual feature was the use of horses for skidding in some opera­
tions (fig. 1).
11 Maintained by the U.S. Forest Service in cooperation with the
Simpson Timber Co.
11 Maintained by the U.S. Forest Service in cooperation with the
St. Regis Paper Co.
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Figure 1.-- The only unusual f e a t u r e was the use of horses for
skidding on some operations.
Description of the thinning jobs (table 1) reveals considerable
variation. Aside from the involvement of seven different contractors
over the 15-year period, there were important differences in crew size
and management skill. Also, there were differences in skidding methods
and machinery, as well as in trucking distance and types of hauling
equipment. These many differences may increase the value of the study,
since any valid inferences are thus more generally applicable.
RECORDS
Daily time records were secured from each contractor, not only for
the overall operation, but for the various functions of felling and
bucking, skidding, loading, hauling, and miscellaneous.
The breakdown
of full daily time on the job included rest time, travel time, and all
delays. At the end of each job, time for each operation \vas compared
with cubic-foot volumei/ produced.
i/ At McCleary, where output was measured in board feet, conversion
to cubic feet was based upon average log diameter produced.
Board-foot/
cubic-foot ratios averaged 5.6 and ranged from 5.4 to 5.8.
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Table 1.--Time and related data for thinning studies, McCleary and Hemlock Experimental Forests
HORSE SKIDDING OPERATION
Experi Year
mental
Forest
Average
Average
d.b.h. of
skidding
thinning
distance
thinnings
- --------
Inches
Feet
Trucking
Total
distance
Total
man-hours
one way
involved
-'------
Cu. ft.
Average time
"Felling
and
bucking
I
Skidding
I
Loading
l
Hauling
J
Miscel laneous
J
Total
----------------- Man-hours per 100 cu. ft. --------------
Miles
Hemlock
9.0
175
12,231
70
684
1.27
1.71
0.96
1.35
0.30
Hemlock
9.0
200 19,536
40
1,158
.80
2.56
.96
1.19
1955
Hemlock
9.3
175
12,276
15
581
.96
2.08
.53
.70
.41
.45
4.72 1960
Hemlock
10.3
225
3,956
15 219
.78 3.06
.53
.81 .35
5.53
1956
Hemlock
11.0
280
20,859
15
949
1.11
1.61
.82
.60
.41 4.55
1957
Hemlock
11.5
300
21,490
15
951
1.05
1.78
.70
.70
.20
4.43 1960
Hemlock
11.9
300
22,671
15
898
.72
1.66
.52
.79
.27
3.96 1959
Hemlock
12.3
280 13,890
20
506
.77
1.14
.58 .79
.36
3.64
3.76
1958
1958
5.59 5.92
CRAWLER T RACTOR SKIDDING OPERATION
I
..,...
I
1960
McCleary
14.1
300 23,244
874
.78
1.29
.64
.79
.26
1955
McCleary
14.3
300
20,439
5
669 .89
1.20
.41 .44
.33
3.27
1957
McCleary
14.3
500
23,539
5
776
.98 .55
.51
.32
3.30
1959
McCleary
14.3
200 22,182
17 812 .73
1.25
.62 .79
.27
3.66
1962
Hemlock
15.4
280
14,298
15 412 .55
1.00
.43
.59
.31
2.88
3.52
17
.94
1951
McCleary
15.6
460
39,107
5
.87
1.28
.53
.33
McCleary
15.7
200
21,091
5
738 .95
.51
1954
.88
.68
.50 3.50
1953
McCleary
16.6
300
34,285
5
996 .67
.96
.35
.47
.49
.46
2.91
TREE FARMER
1,375
(4-WHEEL TRACTOR) SKIDDING OPERATION
.so
.71
.16
3.27
.75
.79
.18 2.86
1.05
1.29
.67
.68
.28
3.97 354
.49
.48
.48
1.00
.20
2.65 633
.64
1.03
.49
.21
2.54
721
.35
.46
.57
1.10
.21
2.69 22 679 .54
.99
.16
.46
.11 2.26
27,838
17
589 .47
.79 .17
.44
.25
2.12
40,672
22 936
.56
.92
.15
.52
.15
2.30
1964
Hemlock
11.1
200
15,932
95
521
.72
1964
Hemlock
12.8
175
17,448
95
499
.64 1963
Hemlock
13.1
300
19,306
15
770
1965
Hemlock
14.6
280
13,351
100
1964 McCleary
15.1
410
24,943
1965
Hemlock
15.1
300
26,785
1965
McCleary
15.1
400
28,955
1962 McCleary
16.5
500
1963 McCleary
17.4
375
22 100
1.21
.47
.17 RESULTS AND DISCUSSION
Total timel/ per unit of volume and amount cut per acre were not
significantly correlated at either location (fig. 2) .
The plotted data at both locations clearly indicate lower man-hour
requirements for Tree Farmer skidding over that for crawler tractors or
horse skidding.
In a recent comparable study in western Washington,.§./ it was also
observed that amount cut per acre had little effect on man-hour require­
ments. This seems consistent with the flexibility of thinning methods
which are characterized by small crews, light and inexpensive equipment,
and high mobility.
This ease and speed of movement reduces time involved in traveling'
from tree to tree and in collecting an efficient turn for skidding to
the landing. Also, improvements in loading procedure, permitting quick
and efficient movements along roads, negate necessity for large-volume
road decks as in the past.
Range of observed data for both locations restricts inferences to
operations removing approximately 5 to 16 cords per acre which, under
current commercial thinning practices, encompass very light to moderately
heavy removal. By grouping the 25 projects by skidding method (table 1) ,
a significant statistical relationship between average d.b.h. removed
and labor requirements for horse skidding (1-percent level) and for Tree
Farmer (5-percent level) was revealed. Crawler tractor showed no sig­
nificance, perhaps due to limited range of data (fig. 3) . As could be
expected, man-hours decreased as d.b.h. increased,
Slope of the regres­
sion lines is quite similar for Tree Farmer and crawler tractor skidding
and much steeper for horse skidding, perhaps because of smaller and less
efficient diameters in this latter method.
As an example of actual man-hours involved in thinning, a 12-inch­
d.b.h. tree average required 3.30 man-hours per 100 cubic feet for the
Tree Farmer method, and horse skidding required 4.01 man-hours or 21
percent more. Since the crawler tractor method was not involved in
diameters be low 14 inches, no direct comparison is possible \vith horse
skidding. Hmv-ever, at this 14-inch diameter, it required 3.56 man­
hours, or 20 percent more, than did the Tree Farmer method at the
same size.
2/ Total time included all functions of the thinning operation
from felling to delivery to the processing mill.
!i/ Horthington, Norman P. Cost of thinning 50-year-old Douglas­
fir for pulpwood at Voight Creek Experimental Forest. Pacific North­
west Forest & Range Exp. Sta. Res. Note 215, 4 pp. 1961.
-5-
SKIDDING METHOD:
X CRAWLER TRACTOR
• TREE FARMER
0HORSE
59 YEAR OF THINNING
)(60
><s9
X 51
n
3
-!-'
<!) ....().
.g()
0
0
....c 064
4163
2
1!065
McCleary
Experimental Forest
41162
""
<!)
058
0.
0 58
0
60
(/)
""
:;j
0
..t:: I
!=:
ro
s
5
v
6
05
.....
£-1
055
0 7
5
4
<
Hemlock
Experimental Forest
0 59
£-1
0
£-1
664
3
><62
•65
600
41>65
064
tOOO
800
CUT PER -AORE ( cubic feet)
Figure 2.--Re/ation of total time per 100 cubic feet to cut per acre,
-6 ­
1,400
6_
Q)
u
0 HORSE SKIDDING
00
I\
....
.!!
0
5
0
.0
::s
u
·-
0
X
0
0
0
•
0
00
0
0
""
Q)
0.
0
4
0o
(I)
""
I
-..j
I
::s
0
..c::
II
I
t::
t1S
s
TRACTOR SKIDDING
TREE FARMER SKIDDING
3
'-.../
•
HORSE
0o
X
)<X.
---)(
)<. --
•
II
X
X
•
-
-
X
rzl
CRAWLER
TRACTOR
•
..J
<
TREE
!FARMER
2
0
1
-----------------------------------9
10
n
12
13
D.B.H.
OF
THINNING
----------------------14
1s
16
(inches)
Figure 3.--Relation of t o t a I time per 100 cubic feet to d.b.h. of thinning.
11
-----18
Labor requirements per diameter class (fig. 3) indicate the superi­
ority of the Tree Farmer in labor efficiency over use of horses or
crawler tractors.
The difference in labor requirements between horses
and tractors appears to be slight, but a good comparison is not possible
Low efficiency
due to lack of overlap on common tree diameters handled.
for crawler tractors in this particular case may be because of larger,
less efficient crews, ill suited to small timber and light cuts (fig. 4).
The higher labor ratio for horse skidding was often partially offset by
the low overhead, smaller crews, and greater adaptability to thinning
by the horse-using operators.
Figure 4.-- The crawler tractor is not well suited to thinning in small
timber and light cuts.
The Tree Farmer skidding method, first used in 1962 (table 1) ,
represents an improvement over the other two methods (fig. 5) . Not
only is less labor required per unit volume harvested but at the same
time it allows a greater efficient-skidding radius, thus reducing
- 8­
amount of roadbuilding required.
This method, or a similar one, may
be expected to predominate in the thinning field, at least in the
immediate future.
Figure 5.-- The Tree Farmer represents an improved method of skidding,
requiring less labor and allowing a greater efficient-skidding
radius.
Diameters used in the above analyses are averages for each thin­
ning method and are valid only for diameter ranges as shown in figure
3. All thinning projects reported were repeats, except for the 1951
and 1953 sales at McCleary and the 1957 sale at Hemlock.
Thus, skid­
roads, landings, and any benefits from greater felling efficiency in­
herent in a previously thinned stand were available for all jobs except
the three cited examples.
Apparently, labor requirements for Tree Farmer thinning are fairly
close to those of harvest of typical old-growth timber (table 2) .
-9 ­
Table 2. --Logging output per man-hour in extraction of typical
old-growth timber and young-growth thinnings in
Oregon and Washington
Old growth])
Job function
West
side
East
side
Young growth·V
(Tree Farmer
method)
Board feet, Scribner Rule
Falling, bucking, yarding,
and loading
Hauling
All job functions
483
586
403
1, 342
1, 095
956
224
277
259
ll Adapted from table 5 of: Smith, Richard c., and Gedney,
Donald R.
Manpower use in the wood-products industries of Ore­
gon and Washington 1950-1963.
Pacific Northwest Forest & Range
Exp. Sta. u.s. Forest Serv. Res, Paper PNW-28, 48 pp. , illus.
1965.
11 Seventeen-inch-d. b. h. average tree.
This comparison is not precise since average old-growth tree diameters
are larger for east- and west-sidell examples as compared with thinning
diameters. Undoubtedly, thinning operations may be in some cases as
efficient as mature timber harvest despite smaller tree diameter be­
cause of no road allowance in the thinning case as opposed to sizable
allowances in mature timber harvest,
Furthermore, smaller crews, al­
most universal use of contract system, and less general overhead
expense inherent in thinning make possible substantial reduction in
overall labor requirements.
The readily accessible areas of young
timqer, which are substantial, thus may be thinned at a labor cost
somewhat comparable to that for harvesting more remote mature timber.
II East and west of the Cascade Range in Oregon and Washington,
-lU-
The relative importance of individual job functions clearly shows
skidding (31-39 percent) and felling and bucking (21 -24 percent) as
the major users of manpower in thinning operations (table 3). Hauling,
loading, and miscellaneous follow in that order. The high figure of
24 percent for hauling under the Tree Farmer method is due to excep­
tionally long hauls experienced on these jobs.
Table 3.--Percent of total time for various job functions in
thinning by three skidding methodsl/
Job function
Horse
Crawler tractor
Tree Farmer
--------------- Percent --------------Felling and bucking
Skidding
Loading
Hauling
Miscellaneous
Total
21
39
14
16
10
24
34
16
18
8
100
100 23
31
16
24
6
100
1/
- Twelve- and 14-inch-d.b.h. average tree for horse and
Tree Farmer methods and crawler tractor method, respectively.
MEANING AND APPLICATION OF RESULTS
1. Since labor requirements are but little influenced by cut per
acre, this item does not require major consideration in laying
out a thinning operation, at least within the range of volumes
studied --400 to 1,300 cubic feet per acre or, roughly, 2,250
to 7,250 board feet. Ability to make light cuttings could
conceivably reduce the interval between thinnings.
2. Labor requirement in thinning decreases with increase in aver­
age d.b.h, of tree taken. Hence, a thinning which yields a
larger tree will make more efficient use of labor than a
smaller tree thinning. Findings of this study may be a useful
guide in marking of trees, timing of thinning, and choice of
thinning method. As an example, in an early thinning when
-11 ­
diameters are close to a marginal economic size, it may be
feasible to thin from above, using a crown or selection thin­
ning, rather than from below, thus starting the thinning
regime earlier.
3. There is a slight trend toward increased labor efficiency in
extraction over the period (19 51 -64) for the entire job. Most
improvement has been in the felling and bucking and loading
operations.
4. More studies are needed in manpower requirements for thinning
young Douglas-fir and western hemlock. Studies which relate
these factors to individual tree diameter would be of greater
value than comparisons with average diameters of entire stand
thinning as presented here. Until such findings are available,
however, rough approximations as presented should prove useful,
It is impossible to intelligently thin or partially cut without
some guides on how size of cut trees may influence labor re­
quirements. Many a thinning operation will fail without serious
consideration of this simple relationship.
* 1< *
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