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Fig. 1. The excavator-based harvester used for the research.

Table 1. Specifications of excavator-base and harvester head used in the study.
Component Specification
Base machine
Make and model Sumitomo SH210
Weight 20 000 kg
Power rating 117.3 kW
Width 2800 mm
Length (without boom) 4810 mm
Height 2960 mm
Ground clearance 440 mm
Boom outreach 8700 mm
Head
Make Waratah 616 C
Weight 1680 kg
Max cutting capacity 55 cm
Saw bar length 75 cm
Number of feed-rollers 3
Feed-roller type steel with angled bars
Number of knives 2 fixed, 3 moving
Hydraulic fluid requirement 320 – 360 l/min
Max hydraulic pressure requirement 35 MPa
Source: Manufacturer specifications
Table 2. Site description.
Plantation Sappi Venus
Compartment A44
Species E. grandis (Coppiced)
Area (ha) 42.0
Age (yrs) 11.0
Average DBH (cm) 21.0
Average Height (m) 33.7
Spacing (m) 2.4 × 2.4
Trees per hectare (after mortality) 1383
Average tree volume (m3) 0.466
Removal per hectare (m3) 645
Original sample size (trees) 769
Ground roughness Smooth
Slope Level to Gentle (less than 20%)
Table 3. Description of time elements of the cutting process.
Time element Description
Moving Any time the tracks were rolling.
Felling Positioning the harvester head around the standing tree, which began when the boom reached out; felling proper, which began when the chainsaw started advancing and ended when the tree started to fall and the head was horizontal, ready to process the tree.
Processing Began when the head was horizontal and included delimbing, debarking and crosscutting. Ended when the last assortment had been processed.
Other work Any other productive time (e.g., removing of obstacles, stacking logs etc.).
Delays Non-productive time, including mechanical, operational and personal delays.
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Fig. 2. Breakdown of worksite time by activity type for single stems (above) and double stems (below).

Table 4. Multiple regression models for time consumption.
Moving
T =      5.147
Felling R2 adjusted = 0.428
Ln T = a + b DBH^2 + c OPB
  Coeff SE T P
a 2.149 0.031 68.635 < 0.001
b 9.389 * 10–4 0.511 * 10–4 18.381 < 0.001
c 0.217 0.048 4.526 < 0.001
Processing (= delimb, debark, cross cut) R2 adjusted = 0.715
T = a + b DBH^2 + c OPB + d OPB * DS
a 19.672 1.038 18.942 < 0.001
b 0.057 0.002 33.871 < 0.001
c 4.942 2.431 2.032 0.043
d 6.653 2.991 2.224 0.027
Cutting (= felling + processing) R2 adjusted = 0.750
T = a + b DBH^2 + c OPB + d OPB * DS
a 26.516 1.227 21.612 < 0.001
b 0.074 0.002 36.944 < 0.001
c 9.038 2.863 3.157 0.002
d 7.295 3.521 2.072 0.039
Other work
T =      1.168
Delays
(Moving + Cutting + Other work) * 0.208
Notations: T = time in s per stem; DBH = Stem diameter at breast height (1.37 m); OPB = Indicator variable for operator B (less experienced): 0 = operator A; 1 = operator B; DS = Indicator variable for double stems: 0 = single stem; 1 = double stem (i.e. stem growing from a stool that supports two stems)
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Fig. 3. Harvester productivity as a function of tree size and treatment (single vs. double stem). DBH = Stem diameter at breast height (1.37 m).