U.S. Department of Agriculture

Forest Service

Research Paper SO- 14 1

Harvesting Costs

For Mechanized Thinning Systems

In Slash Pine Plantations

JAMES E. GRANSKOG
Summary

Harvesting costs of four tree harvester systems were

estimated for row thinning l&year-old slash pine

plantations. Two full-tree harvester systems had lower

harvesting costs per cord than shortwood harvester and

tree-length harvester systems. The shortwood and treelength harvester systems had lower manpower requirements, but their high capital cost in relation to output

resulted in higher harvesting costs when compared to

the full-tree harvester systems.

1978
Harvesting Costs for Mechanized Thinning

Systems in Slash Pine Plantations

JAMES E. GRANSKOG

The vast southern pine plantation acreage now in need of its first commercial

thinning has spurred the development of specialized tree harvesting machines.

Currently, tree harvesters are mainly used on company operations of pulp and

paper firms owning large acreages of plantations. However, independent contractors, who do most of the timber harvesting in the South, must also adopt

such machines if thinning requirements are to be met. Furthermore, many

contractors are located in areas where plantations are concentrated and will

likely be the most commonly available stumpage.

Production and cost information are needed for selecting the most suitable

machines for specialized thinning operations. This report estimates harvesting

costs for four tree harvester systems designed to row thin slash pine plantations. These estimates can be used to compare systems or to determine economical thinning opportunities for a given system.

Systems and Procedures

Tree harvesters may be classified into three general types according to the

form of their output-shortwood, tree-length, and full-tree. That is, the output

from the machines will be a bunch of bolts (shortwood), bunched tree-length

logs (tree-length), or bunched trees (full-tree). Because the functions performed

by each type of harvester are different, measures of output and cost are not

directly comparable among the machines. However, the harvesters can be

compared by considering them as a part of systems that carry wood to a common delivery point. Evaluation of the systems takes into account the supporting equipment and labor needed with each type of harvester. Evaluating

the harvesters on a systems basis also makes possible comparisons of proposed harvesting systems with existing ones.

The following thinning systems were selected to permit estimates of investment, harvesting cost, and productivity:

A) shortwood havester/forwarding/shortwood hauling

B) tree-length harvester/grapple skidding/tree-length hauling

C) full-tree harvester/chain saw limbing and topping/grapple skidding/treelength hauling

II) full-tree harvester/chain saw limbing and bucking/forwarding/shortwood hauling.

These options are typical combinations with each of the harvesters. Two

options for processing and handling wood with the full-tree harvester were

selected, since further processing of bunched trees is required with this machine.

,

James E. Granskog is Economist at the Southern Forest Experiment Station, Forest

Swuice- USDA, New Orleans, Louisiana.
The procedures used for determining system requirements and estimating

harvesting costs were the same for all systems. Output rates of the harvesters

were obtained for row thinning slash pine plantations and were adjusted to

reflect the same performance criteria. Harvester output determined the supporting equipment and men added to complete each system. Assumptions

made for skidding and hauling distances and for computing labor and equipment costs were the same for all systems.

System Requirements

Any harvesting system should be designed around the most expensive or

key piece of equipment. In a mechanized thinning system, the production

of the harvester controls the output rate of the total operation. Therefore,

productivity rates of the harvesters can be used to determine the additional

equipment and men needed to make-up a system.

Productivity estimates for machines representative of the three types of

harvesters being evaluated have been reported for row thinning slash pine

plantations (Anderson and Granskog 1974). Table 1 shows hourly production

rates, by harvester type, for selected stand conditions in 15year-old plantations, a common age for thinning. These production figures, however, represent potential output without allowance for downtime or idle time. For this

analysis, a 75-percent utilization standard is assumed for each harvester.

To complete each system, supporting equipment and men were selected

by determining for each function the number of units required to handle

the daily output produced by the harvesters. To insure that harvester output

was the limiting factor, the stand condition where production was greatest -

site index 70 with 500 trees per acre-was the output level for determining

supporting requirements. With the utilization factor applied, these production levels on a daily basis are shortwood, 24.2 cords; tree-length, 35.4 cords;

Table l.-Tree harvester productivity for selected stand conditions in 15-yearold slash pine plantations’

Site Total trees

index per acre

60 500

600

700

800

70 500

600

700

8nn

Harvester type

Shortwood Tree-lengths Full-treed

______________-_ Cordsperhour_______________

3.49 4.73 8.87

3.40 4.19 7.96

3.35 4.04 7.87

3.21 3.67 7.79

4.04 5.87 9.99

4.01 5.13 8.84

3.90 4.72 8.20

3.75 4.27 8.06

1 Anderson and Granskog 1974.

2 7-foot bolts in approximately l/3-cord piles.

3 Bunched tree-length logs, 4-5 trees per bunch.

4 Bunched trees, 4 trees per bunch.

2
and full-tree, 59.9 cords. Production rates for skidding, loading, and hauling

equipment were then compared with these levels to determine the number of

units required.

Total system requirements are summarized in figure 1. Skidding of 660

feet and hauling distances of 30 miles were assumed in all cases. Separate

loaders are required in two systems to place tree-length material on hauling

units; shortwood is unloaded by the prehaulers directly onto set-out trailers.

More trucks are needed to transport tree-length material than shortwood

because the short length of plantation stems does not fully utilize trailer

capacity. Wicking requirements were based upon 7-cord loads for tree-lengths

and lo-cord loads for shortwood.

In the shortwood and tree-length harvester systems, felling and processing

are completed by the harvesting machines. The two systems incorporating

the full-tree harvester require chain saw operators for processing the bunched

trees. It is estimated that two men would be needed to limb and top treelength logs, and four men would be required for limbing and bucking 7-foot

shortwood.

Production manpower requirements for each system, following the letter

designations in fig. 1, are: A-3 men, B-4 men, C-8 men, and D-9 men.

Tree-length wood is loaded by the truck drivers.

System Costs

Harvesting cost estimates for each system may be computed by calculating

hourly system costs and using production rates from table 1 with adjustment

for the 75-percent utilization standard assumed.

A synopsis of system costs is contained in table 2. Investment figures are

based on prices of new machines in 1977, except it was assumed that treelength loaders would be mounted on used trucks. Major assumptions for

computing machine costs were 5-year depreciation for all equipment (except

l-year depreciation for chain saws), 20 percent salvage value, and 14 percent

of the average annual investment for interest, insurance, and taxes. Repair

and maintenance charges were 100 percent of the purchase price. Fuel, oil,

and lubrication costs were also included. Labor costs were determined by

multiplying the number of men required in each system by a $5.50 per hour

cost, which included wages and charges for social security, workers’ compensation, and unemployment insurance.

Table 2. -System costs

System Initial

investment Machine

Hourly costs

Labor Total

A $148,700 $37.92 $16.50 $ 54.42

B 198,500 52.39 22.00 74.39

C 203,200 58.64 44.00 102.64

D 173,200 50.13 49.50 99.63

3
4
Table 3.-Estimated harvesting costs per cord of four tree-harvester systems for selected

stand conditions in 15-year-old slash pine plantations

Site Total trees

index per acre

60 500

600

700

800

70 500

600

700

800

Harvesting systems

A B C D

_________.____ __Cos~percor~____.______.____

$20.77 $20.95 $15.43 $14.98

21.34 23.69 17.19 16.69

21.68 24.55 17.40 16.87

22.58 27.05 17.58 17.06

17.96 16.91 13.70 13.30

18.08 19.32 15.48 15.03

18.57 21.01 16.69 16.20

19.37 23.25 16.97 16.47

Cost-per-cord estimates (table 3) were obtained by dividing hourly system

costs (machine plus labor) by hourly system outputs (harvester production

rates adjusted for 75-percent utilization) for the selected stand conditions.

Stumpage and administrative expenses are not included in the cost-per-cord

estimates. Manpower productivity figures are shown in table 4.

For all systems, productivity decreases and harvesting costs increase as

site index drops from 70 to 60 and stand density increases. This is because

tree size declines as site index decreases and stand density increases.

Both full-tree harvester systems cost less per cord than the shortwood

harvester and tree-length harvester systems, even though the latter two are

more advantageous in man-day productivity. Although the shortwood and

tree-length machines reduce manpower requirements, the high capital cost in

relation to their output compares unfavorably with the full-tree harvester

systems. The capability of the full-tree machine to put considerably more

wood on the ground and allow processing of bunched stems by chain saw

operators results in lower harvesting costs.

Table 4.-O&p& per man-day of four tree harvester systems for selected stand conditions

in 15 year-old-slash pine plantations

.~___

Site Total trees Harvesting system

index per acre A __~_ B C D

___-____--__ Cords per man-day - - - - - - - - -

60 500 7.0 7.1 6.6 5.9

600 6.8 6.3 6.0 5.3

700 6.7 6.1 5.9 5.2

800 6.4 5.5 5.8 5.2

70 500 8.1 8.8 7.5 6.7

600 8.0 7.7 6.6 5.9

700 7.8 7.1 6.2 5.5

800 7.5 6.4 6.0 5.4

5
Discussion

From the standpoint of harvester selection, the cost per cord estimates

presented here indicate a full-tree harvester has an advantage over other

types of harvesters for the stand conditions considered, whether it is combined with shortwood or tree-length supporting equipment. When upgrading

an existing system, a full-tree machine would be favored to go with either

type of supporting equipment that is being used.

Assembling a new system would permit a choice in the type of supporting

machines used with the harvester. Although the shortwood option has slightly

lower costs among the two alternatives examined, the cost-per-cord estimates

for the conditions considered were based on fixed skidding and hauling distances. The effect on total costs as these factors change should be considered

in the selection of auxiliary equipment, as well as other factors that may

vary between systems.

For example, a prehauler is more cost-effective when long skidding distances

are involved because it has a larger capacity than a grapple skidder (typically two cords vs. one cord or less). This offers greater versatility in harvesting small or isolated tracts. Landing costs are minimized with a prehauler

system because set-out trailers may be parked along truck roads without

construction of a large landing area. A prehauler also can maneuver in a

stand with less damage to standing trees than a grapple skidder with a load

of tree-length wood.

Alternatively, a grapple skidder with a full-tree harvester may offer more

development flexibility. For instance, an iron gate delimber is a simple, costeffective means of eliminating manual delimbing with a grapple skidder

(Bryan 1977). Also, a full-tree harvester/grapple skidder combination can be

upgraded into a whole tree chipping operation.

The potential of any harvesting system can be lost by poor planning and

administration. A good maintenance program is essential to obtain the machine availability necessary for a successful mechanized operation. Downtime

can be minimized by careful planning. For instance, the harvester is the limiting

machine in the systems considered. Operating the harvester a few days ahead

of the rest of the equipment would help avoid total shutdowns and improve

system reliability. The lead time insures a supply of felled wood for other

functions when the harvester is idled for repairs.

Adopting a mechanized thinning system, of course, requires a large capital

investment. Many independent operators today may not be willing or able

to undertake the investment required to perform all of the functions of the

harvesting operation. One approach to this problem may be to encourage

machine operators who become proficient in a function to purchase their own

machines. Truck drivers and harvester and prehauler operators who have

the inclination to operate their own businesses could specialize in that capacity for a number of other wood producers.
Literature Cited

Anderson, W. C., and J. E. Granskog

1974. Mechanized row-thinning systems in slash pine plantations. U.S. Dep.

Agric. For. Serv. Res. Pap. SO-103, 12 p. South. For. Exp. Stn., New

Orleans, La.

Bryan, R. W.

1977. Delimbing gate. For. Ind. 104(7): 93.

Granskog, James E.

1978. Harvesting costs for mechanized thinning systems in

slash pine plantations. U.S. Dep. Agric. For. Serv. Res.

Pap. SO-141, 7 p.

Harvesting costs of four tree harvester systems are estimated

for row thinning slash pine plantations. Systems incorporating

a full-tree type harvester had lower harvesting costs per cord

than shortwood and tree-length harvester systems in 15-yearold plantations.

Additional keywords: Bee harvesters, mechanization, productivity, and logging costs.

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