Research No&“~*~~

1981

Dense Undergrowth Reduces Feller-Buncher Productivity

In Shortleaf Plne Plantations

James E. Granskog and Walter C. Anderson

SUMMARY

Production rates of a feller-buncher are shown for

row thinning pine plantations with light and dense

undergrowth conditions. Dense undergrowth reduced

macliine output by about 20 percent.

Additional keywords: Row thinning, timber

harvesting, tree harvester.

Feller Buncher (fig. 1). This machine was equipped

with a 164nch capacity shear and an accumulator

arm. In operation, two arms hold the tree while it

is severed at ground level. The accumulator arm

allows several small trees to be gathered before the

stems are deposited on the ground.2 Severed trees

are carried and piled until the desired bunch size

is created.

INTRODUCTION

Plantations of loblolly and shortleaf pine frequently

have understories of hardwood brush. On some sites,

in the absence of control measures, small hardwoods

and other vegetation can become quite dense. As

part of a study of mechanized row thinning of pine

plantations, we investigated whether understory hardwoods might have an impact on harvesting operations.

This note reports the effect of hardwood undergrowth on the productivity of a feller-buncher for row

thinning shortleaf pine plantations. Feller-bunchers

are the most common type of mechanical harvester

used in row thinning. In row thinning, undergrowth

will most likely affect productivity in the felling

phase of the operation, since the harvesting of entire rows provides convenient roads for skidding

machines. Other factors being equal, shortleaf plantations may have a large number of hardwoods in

the understory because of the slow early growth

of the pine.

The machine studied was a Melroe Bobcat 1075

Data were gathered in time studies to develop

regression equations for predicting processing times

under different undergrowth conditions.

Data collection took place in two pine plantations

in central Tennessee. A shortleaf plantation located

adjacent to a minor stream bottom had a dense

hardwood understory, while an adjoining loblolly

plantation contained only light undergrowth. Other

environmental conditions were the same; terrain

was generally flat and soil conditions were dry.

A thinning operation was removing every third row

in the plantations. Time and output measurements

were obtained on line-segment plots installed in

‘Mention of the trade names is solely to identify equipment

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

of Agriculture.

2The accumulator on the observed machine was used sparingly;

hence, study data essentially represent the operation of a singletree feller-buncher.

Southern Forest Experiment Station/T-10210 U.S. Postal Services Bldg., 701 Loyola Avenue, New Orleans, La. 70113

Forest Service, U.S. Department of Agriculture.

Serving Alabama, Arkansas, Louisiana, Mississippi, Eastern Oklahoma, Tennessee, Eastern Texas.
Figure 1 .-Me/roe bobcat 1075 feller-bunchetz

rows prior to felling. All data collected were with

the same machine and operator.

Thirty sample plots were harvested in each plantation. Before cutting, length of segment, dbh of

each tree, and total tree height were measured.

Total time required for the machine to fell and pile

the trees on a plot was recorded. In addition, log

lengths and top diameters were measured after chain

saw operators had limbed and topped the trees.

Numerous vines and thick hardwood brush reduced

visibility for the machine operator while he harvested

rows of shortleaf pine (fig. 2). Saplings also restricted

maneuverability, and a few stems 3-4 inches dbh

required shearing and removal. Hardwood brush

Table 1 .-Equations for estimating feller-buncher performance

encountered in the loblolly plantation, however, was

small and scattered.

Two undergrowth conditions-dense and lightwere recognized. Data collected in the shortleaf

plantation reflected machine performance with dense

undergrowth, while data from the loblolly plantation

represented performance with light undergrowth.

Estimating equations were developed from the

measurements taken in each undergrowth category.

The dependent variable was time, expressed in minutes per hundred feet of plantation row. Other data

were also converted to a hundred-foot basis. Independent variables tested for significance were:

1. Number of trees.

2. Average dbh.

3. Average of the dbh squared.

4. Sum of the log lengths.

5. Sum of the log lengths/average of the dbh

squared.

6. Average of the dbh squared/average of dbh.

Variables 5 and 6 were significant at the 1 percent

level. Variable 5 has characteristics that account

for tree volume and weight. Variable 6 is a measure

of dispersion of tree size around the mean. Resulting

equations for the two undergrowth conditions are

shown in Table 1, along with measures of goodness

of fit.

A covariance analysis of the regressions showed

no difference in slopes, but a significant difference

in intercept values at the 0.01 level. That is, the

effect of the undergrowth is reflected largely by

the difference in the constant terms.

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

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

of operation.

Undergrowth

class Estimating equation

Dense y=- 7377+.58qzL+ ~)+1.140(~)

Light Y=-3*097+.415(PL+ y)+.503(#)

Y =Time per 100 feet of row, in minutes.

D=Dbh, in inches.

L =Log length, in feet.

N=Number of trees.

RZ S E

.72 1.28

.84 .78

James E. Granskog and Walter C. Anderson are Research Foresters. Southern Forest Experiment Station, Forest Service-USDA,

New Orleans, Louisiana.

2
Figure 2.-Dense undergrowth obscured the row being removed. A felled tree lies adjacent to the leave

row on the right,

To illustrate the effect of undergrowth on machine

productivity, the equations were used with stand

and yield data for shortleaf pine to calculate hourly

production rates for plantations with each undergrowth condition.

Detailed stand structures for unthinned shortleaf

pine are available from Smalley and Bailey (1974).

The tables used were for plantations age 20 with

a site index of 50 (25-year basis) and densities ranging from 750 to 1,250 trees per acre. Merchantable

trees were limited to those in the 4-inch diameter

class and larger, and tree lengths and volumes were

computed to a 3-inch top diameter. Stand characteristics for each density were entered into the

estimating equations to derive processing times per

hundred feet of row.

Processing times were used to calculate potential

hourly output for each stand situation. It was assumed

that the feller-buncher would be working in a 40-

acre tract with rows 1,320 feet long, and with a

grapple skidder as supporting equipment. To limit

skidding distance, the feller-buncher would cut half

of the row with butts facing one way and half facing

the other. It would do this by entering a row from

one end, cutting 360 feet, returning to the end of

the row, and then entering the next row to be removed. An allowance for return time was made, but

not for downtime or idle time. Thus, hourly production figures represent potential output; that is, at

100 percent machine utilization. To obtain realistic

4 I 1 I 1 1

780 1.000 1,250

TREES PER ACRE

Figure &--Effect of undergrowth conditions on hour/y output of

feller-buncher row thinning shortleaf pine plantations

(age 20, site index 50, rows d-feet apart).

3
production levels for longer time periods or an

average hourly rate, such figures must be adjusted

for the probable utilization rate.

Machine productivity, in cords per hour, is shown

in Figure 3 by stand density for dense and light

undergrowth conditions. Output is in the form of

bunched trees. Results indicate production rates for

the feller-buncher are about 20 percent less when

row thinning pine plantations with dense hardwood

undergrowth as opposed to light undergrowth.

This study revealed dense hardwood undergrowth

conditions significantly reduced the production rate

of a feller-buncher used in row thinning southern

pine plantations. The effect of undergrowth may be

different for other machines or thinning methods.

Monitoring harvesting operations is necessary to

identify the relative importance of undergrowth and

other environmental factors on system productivity

and cost.

DlSCUSSlOiU

LITERATURE CITED

Overall, mechanization has probably reduced the

sensitivity of timber harvesting operations to most

environmental conditions. Some machines, nevertheless, are adversely affected by particular factors.

The identification of such factors and their influence

on productivity is important in machine selection

and for estimating harvesting costs.

Smalley, G. W., and R. L. Bailey.

1974. Yield tables and stand structure for shortleaf

pine plantations in Tennessee, Alabama, and

Georgia highlands. U.S. Dep. Agric., Forest Service, Res. Pap. SO-97, 57 p. South For. Exp.

Stn., New Orleans, La.