U.S. Department of Agriculture 

Forest Service 

Research Paper SO-163 

Harvester Productivity for Row Thinning 

Loblolly Pine Plantations 

James E. Granskog 

and 

Walter C. Anderson 
SUMMARY 

Tivo tree harvesters currently being used to thin southern pine plantations were evaluated 

to determine the effects of stand characteristics on machine productivity. Production rates 

for row thinning loblolly plantations are presented by stand age, site index, and stand density. 

ACKNOWLEDGMENT 

Cooperation in the form of timber, manpower, and equipment was received 

from Hiawassee Land Company and Sherer Timber Company. 
Harvester Productivity for Row Thinning Loblolly Pine Plantations 

James E. Granskog and Walter C. Anderson 

INTRODUCTION 

Plantation thinning has been a focus for mechanization efforts in southern timber harvesting over the past 

decade. This attention bas stemmed from anticipated 

increases in thinning requirements - due to extensive 

planting under the Soil Bank Program and by forest 

industry -and unfavorable trends in labor supply and 

wage rates. Also, relative uniformity of tree size and of 

spacing in plantations favors mechanical row thinning. 

As harvesting systems become more capital-intensive, however, it becomes increasingly important to 

match machines and timber if harvesting costs are to 

be kept in line. Costs will soar if expensive equipment 

is used where its productivity is impaired. Rapidly 

escalating capital costs can make new machines uneconomical in many types of stands. Therefore, it is 

important to know the costs of operating alternative 

mechanized thinning systems and the ways stand 

characteristics and thinning specifications affect them. 

Production rates for key machines are necessary to 

derive these costs. Such rates allow users to apply 

current dollar values to estimate probable operating costs. 

In this study, productivity of two types of tree 

harvesters currently used for row thinning loblolly 

pine plantations was evaluated. The objective was 

to determine the effects of stand characteristics on 

machine productivity. The results, together with those 

from a previous study (Anderson and Granskog 1974), 

provide basic productivity information for the principal types of tree harvesters being used to thin pine 

plantations in the South. 

MACHINES 

Tree harvesters may be classified into three general 

types by the form of their output-shortwood, treelength, and full-tree. Machines studied for this report 

were representative of the tree-length and full-tree types. 

During data collection, shortwood harvesters were not 

being utilized to row thin loblolly pine plantations. 

- 

Granskog and Anderson are principal economists, Southern Fa 

Louisiana. 

The tree-length harvester was a Timberjack RW-30,' 

which had been modified to include some of the improvements designed into the newer model TJ-30 (fig. 

1). The machine can handle trees with stump diameters 

not exceeding 14 inches. In a processing cycle, an 

articulated felling arm severs the tree and lifts it 

back to a horizontal position on the delimbing assembly. 

The delimbing head/boom has a 33-foot delimbing 

str~ke,~ which can be extended 9 to 10 feet by advancing or lowering the felling arm. When delimbing is 

completed, the tree is topped and deposited in a carrier 

on the side of the machine. A cord of stems can be 

accumulated before being dumped on the ground. 

The full-tree harvester was a Melroe Bobcat 1075 

Feller Buncher (fig. 2). This machine was equipped 

with a 16-inch capacity shear and an accumulator arm. 

In operation, two arms hold the tree while it is severed 

at ground level, and the accumulator arm allows several small trees to be gathered before the stems are 

deposited on the gr~und.~ Severed trees are carried and 

piled until the desired bunch size is created. 

PROCEDURES 

Data Collection 

Production data were obtained through time studies 

of machines in ongoing thinning operations in central 

Alabama and Tennessee. Operating conditions were 

similar in each case; terrain was flat to slightly rolling. 

and undergrowth was light to moderate. All data for 

each machine were taken by the same experienced 

operator. 

lMention of trade names is solely to identify equipment used 

and does not imply endorsement by the U.S. Department of 

Agriculture. 

'The operator on the observed machine shortened the basic 

delimbing stroke by positioning the delimbing head near the 

base of the crown of the incoming tree, so needless processing 

of the clear stem was eliminated. 

3The accumulator on the observed machine was used only with 

5-inch dbh or smaller trees because of the difficulty of maneuvering with multiple stems of larger size. 

arest Experiment Station, Forest Service-CSDA. Sem Orleans, 
Time and output measurements were obtained on 

plots installed in rows to be cut. Plots were line segments selected to cover a range of tree diameters and 

spacing intervals. Segment length was limited by the 

extent of urrifcrl-mitt of the tree diameters and intervals 

between trees. 

%enty-seven sample plots were harveszed by the 

tree-length machine and 30 by the full-tree harvester. 

For each plot, the foliorving information was recorded 

before cutting. 

I. Length of segment from the first tree to be cw~ 

to the first tree beyond the segment, measured 

to the nearest tenth of a foot. 

2, Dbh of each tree, measured to the nearest tenth 

of an inch. 

3. Total kelght of each tree, measured to the 

nearest foot. 

During harvesting of the trees on a plot. total time 

required was measured from the moment the first tree 

was sheared uncil the first tree be>und the segment 

was sheared. Times were recorded to the nearest 

hundredthf a minute. In addition, log lengths and 

top diameters were measured after the tree-lengt8- 

harvester had completed processing trees on 2 plot 

Analysis 

Estimating equati~ns were iievc.icpc;d from the measurements talcen with each harvester. The object was 

to relate the time required to har-enst a specifies 

length of plantation row to the chbracteristics or^ the 

trees cut. 

A stepwise regression procedure was used to select 

the best prediction equation. The dependent variable 

was time, expressed in minutes per hundred feet of 

Figure 1. - Timberjack R W-30 trce-length haruesteiplantation row. Other data were also converted to a 

hundred-fort basis. Independent variables tested for 

&gni -* = .ee were: 

i S~mber c;ftrees. 

2. ili erage dbh, 

3, Average of the dbh squared. 

4. Total length of stems cut. 

5. Total Length of stems cutiaverage of the dbh 

squared. 

6. A; erage of the dbh squared~average dbh. 

Total tree heights and sum of log Ic~gths were used 

as two alternative measures of tohai length of sterns 

eut. depending on the form of output from the harvester. 

Resulting equations for the harvesters are shown in 

table I, together with measures of goodness of fit. 

For t?ae tree-length machine, variable 4-total length 

of merchantable sterns-was the single significant 

variable, indicating the delimbing function explained 

most of the variation, Other differences, such as tree 

-ti eight, did not significantly affect this machine'within 

the range of diarneters harkested. Kumber of trees 

mas a single significant variable for the full-tree 

machine. kl~i this %as rejected in favor of variables 

that included measured tree characteristics. In the 

absewe of variable I, variable. 5 and 6 were found 

to be ssgnificant Po?- the full-tree harvester. Variable 

3 was ii,:ghlliy c~rreiated ~lth the number sf trees. 

and ~ariable 6 is a measure of dispersion of tree 

s:ze around the nea;?. AI; sariabies uere significant 

at the one percent level. 

Table 1. -Estimating equations 

Harvester Equation Rz SE 

Tree length Y= 1.:37:3+ .011351111) .89 .6% 

In' ZD!? Full-tree Y= -3.622t ."8iZFi-- - )+ .614(- j .81 .8,; N ZD 

Y = Time per 100 feet in minutes 

D = Dbh In inches. 

Hz nee height in feet 

L = Log length in feet. 

i?J= Number of trees. 

The equations apply to productive time only. Therefore. allclmance must be made for downtime, idle 

tirne, and turn-around time. depending on the method 

of operation. 

PRODUCTIVITY 

To detrrm:ne hau productivltj mill ~arj in different 

plantaticins the equations itere used ~ith stand s-cructure and yleid data to ea:cuiate i~auriy production rakes 

for each machine. 

Detalled stand structures tor unthinlled lobloll pine 

plantations were ohtalced from Lenhart and Clutter 

(197l), vthich pro~ides diarneten; height, and yield in- 
Potential output in cords per hour for the tree harvesters in plantations with 6- and 8-foot spacing between rows is shown in figures 5 through 6. For both 

machines, productivity increases as both stand age and 

site index rise. These increases reflect volume gains due 

to larger average stand diameters and a larger number 

of merchantable trees. Output is also greater in both 

instznces with 8 feet between rot%§ rather than 6 feet. 

For a given density this reflects closer within-ron 

spacing, or less travel time, as well as more room to 

maneuver. For each site index and stand age, tree size 

declines as stand density increases; therefore, machine 

productivity also drops, although less so for the treelength harvester than the full-tree machine. 

Different production levels for tho harvesters result 

from the amount of processing done by each machine. 

Although expressed in cords. output from each harvester is in a different form. 

The production rates shown represent hourly crt~cpur: 

at 100 percent nrachine utilizition. As such, the! stre... 

variation as stand conditions change. To obtain rtniistic production levels for a specified time period, the 

productivity figures should be adjusted for the proLable utiIizrrtion rate. The appropriart percentage deduction from the hourly rates charted depends upon 

machine availability records and operating procedure. 

Figure 2 -Pifelroc, BOOCLZ~ 1075 feli~r-iir,ncher where the machine will be employed. 

formation by stand age, site index, and density, '&bles 

were chosen for plantation ages 15 and 20 ye- WS, a 

range which covers the preferred age for a firsi cornmercial thinning. Site indexes of 60 and 70 at 25 years 

were selected since they represent the preponderance of 

lobloily pine sites. Densities ranged from 500 to 1,000 

trees per acre for each age and site index. 

For each density class, intervals between merchantable trees within rows were calculated for plantations 

spaced 6 and 8 feet between rows. hlerchantable trees 

were limited to those in the 4-inch diameter class 

and larger, and tree lengths and volumes were cornputed to a 3-inch top diameter. Stand characteristics 

for each situation were then used with the estimating 

equations to obtain the processing times per hundred 

feet of row. 

Processing times for the various stand situations 

were used to calculate potential hourly output. It was 

assumed chat the harvesters xniould be working in a 

40-acre cract with rows 1,320 feet long, csing grapple 

skddders as supporting equipment. ah limit skidding 

distance, the harvesters would cut half of the row with 

butts facing one way and half facing the other. They 

svould do this b>- entering a row from one end. cutting 

660 feet, returning to the end of the row. and then 

enatering the next row to be removed. Thus, an allowance 

for return time, an integral part of the operation, was 

made in computing hourly output. 

COSTS 

In the absence of stable prices. harvesting cost figures quickly become outdated. Ho~vever, the production 

rates presented in physical terms ailow users to apply 

current dollar values to estimate costs for each machine. 

Harvester costs per cord can be estimated by caiculating an hourly machine cost for current prices and 

dividing by the hourly output of the inachine for a 

selected plantation situation. For example, suppose 

the cost of row thinning a 20-year-old plantation with 

site index 60 and containing 800 trees in rows 8 feet 

apart is desired for the tree-length harvester. Figure 4 

shows the potential hourly output for this stand to be 

6.6 cords. Appljing a 75 percent utilization factor indicates an houri) production rate of 4.9 cords. iZssurre 

an hourly machine cost of $30 has bcex derived using 

current prices and nages. 1)i.cidiilg the $30 hiai~rip 

machine cost bj the 4.9 hourij output re\-cz!~ dn 

estimated $6.12 bar\ ester cost per cord 

Sirnce the output from each harvester is in ; dilferiint 

stage of production, costs per cord ;ire not directly 

comparable. Hou:ever the harvesters can be compared 

by considering them tis a part of s> stems thac carr> 

wood to a common deliver? point rGranckog "9;s). 

Evaluating the hart esters on a systems basis take5 

Into account the supporting equipment and labor 

needed with each type of harvester. Since harvester 
-----------____ SITE 70 - AGE 20 YEARS 

SITE 60 - AGE 20 YEARS ---__--- 

SITE 70- AGE 15 YEARS I 

SITE 60 - AGE 15 YEARS 1 

I I 4l I I I I 

500 600 700 800 900 1,000 

TREES PER ACRE 

Figure 3.-Potential hourly output of the tree-length harvester 

with rows 6 feet apart. 

5l I I I I I] 

500 600 700 800 900 1,000 

TREES PER ACRE 

SITE 60 - AGE 20 YEARS ------ ------_-, 

SITE 70 -AGE 15 YEARS 

___---.------ 

SITE 60 - AGE 15 YEARS 

4l I I I I I 

600 700 800 900 1,000 500 

TREES PER ACRE 

Figure 4.-Potential hourly output of the tree-length harvester 

with rows 8 feet apart. 

Figure 5.-Potential hourly output of the full-tree harvester 

with rows 6 feet apart. 

Figure 6.-Potential hourly output of the full-tree harvester 

with rows 8 feet apart. 
production will control the output rate for the total 

system, comparing productivity rates for supporting 

equipment and labor to harvester output rates will 

determine the number of units needed. Hourly costs 

computed for all units can then be combined to obtain 

hourly system costs. These system costs are divided 

by hourly system outputs (utilization adjusted harvester production rates) to derive comparable harvesting costs. 

DISCUSSION 

This study determined production rates for two types 

of tree harvesters being used to row thin loblolly pine 

plantations. As noted earlier, a previous study (Anderson and Granskog 1974) provided the same information for three types of harvesters operating in slash 

pine plantations. Machines representative of two harvester types - tree-length and full-tree - were covered 

in both reports. 

Even between machines of the same type, comparisons of production rates should be made carefully 

because of different operators and differences in stand 

characteristics between species for a given site, age, 

and density. In spite of these limitations, some distinction in production patterns within each type was evident because of variation in machine design. 

The design of the tree-length harvester previously 

observed row thinning slash pine plantations required 

processing the full length of the tree stem. In contrast, 

the design of the tree-length machine studied in this 

report enabled the operator to eliminate needless processing of the clear stem. As a result, there was less 

decline in production for the latter machine as tree 

size declined. (In some instances, the operator merely 

topped trees of small size, omitting delimbing time 

altogether. ) Furthermore, this machine permitted accumulation of a larger bunch size, which can increase 

production of supporting skidding equipment. 

The full-tree machines differed in the accumulating 

function. Although the machine observed in the present 

study was equipped with an accumulator arm, it was 

used on only one plot. Hence, the production rates for 

the machine essentially represent that of a single-tree 

feller-buncher. On the other hand, the full-tree machine 

from the previous study accumulated trees continuously on the side of the machine (from 2 to 7 trees, 

depending on size) between dumps. A comparison of 

production rates shows the single-tree machine had 

lower productivity with trees less than 6 inches dbh, 

but higher productivity with trees over 7 inches. Thus, 

while the accumulator was important for maintaining 

production among smaller trees, its use with larger 

trees was counterproductive. 

The results of this study show the influence of tree 

and stand characteristics on machine productivity, but 

other factors will also affect output and cost. Machine 

operators and machine designs have been mentioned, 

along with species. Terrain, underbrush, and machine 

maintenance are also considerations. Such factors may 

cause machine productivity to vary from the output 

levels shown herein for a given site, resulting. of course, 

in cost variation. In addition, other items must be 

evaluated for their effect upon total cost. For instance, 

tract size and moving costs are important considerations. The latter costs are especially needed for determining the economic feasibility of the minimum job 

for a particular machine or system. Ultimately, the 

planning and administration of the complete harvesting system will determine profit or loss. 

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. 80-103, 12 p. South. For. Exp. Stn., New 

Orleans, La. 

Granskog, J. E. 

1978. Harvesting costs for mechanized thinning systems in slash pine plantations. U.S. Dep. Agric. 

For. Serv. Res. Pap. SO-141,6 p. South. For. Exp. 

Stn., New Orleans, La. 

Lenhart, J. D. and J. L. Clutter. 

1971. Cubic-foot yield tables for old-field loblolly 

pine plantations in the Georgia Piedmont. Ga. 

For. Res. Counc. Rep. No. 22 -Series 3, 12 p. 
GRANSKOG, JAMES E., and WALTER C. ANDERSON. 

1980. Harvester productivity for row thinning loblolly pine 

plantations. U.S. Dep. Agric. For. Serv. Res. Pap. SO-163 

5 p. South. For. Exp. Stn., New Orleans, La. 

Two tree harvesters currently being used to thin southern pine 

plantations were evaluated to determine effects of stand characteristics on machine productivity. 

Additional key words: Mechanization, timber harvesting, logging 

costs. 

* U S GOVERNMENT PRINTING OFFICE 1980-771 -081