Table 1. Forest compartment-level inventory data for merchantable trees on the two harvest sites provided by the landowner.
QMD a (cm) Trees ha–1 Basal area (m2 ha–1) Tonnes ha–1
Compartment estimate 18.2 1435 37.1 208
a QMD = quadratic mean diameter.
Table 2. Cycle definitions and variables recorded during the elemental time studies of the harvester and forwarder.
Machine Functions Cycle definition Variables
Harvester Felling and processing Began when the last piece (i.e., log) of a processed tree was placed on the ground and ended when the last piece of the next tree was placed on the ground Cycle time
Delay time
Pieces tree–1
Volume tree–1 (m3)
Species
Forwarder Primary transportation Began when the empty forwarder exited the landing and ended when the forwarder completed unloading the next load and exited the landing Cycle time
Outhaul time
Inhaul time
Moving time
Loading time
Unloading time
Delay time
Forwarding distance
Time spent at each stop
Number of grapple loads at each stop
Number of logs picked up at each stop
Loading Began when the forwarder contacted the first log to be placed on the trailer and ended when the last log was placed on the trailer Cycle time
Delay time
Time spent loading front trailer bay
Time spent loading rear trailer bay
Hot loading or cold loadinga
Number of logs loaded
a Hot loading refers to loading a trailer directly from the forwarder while cold loading refers to loading logs previously stacked on the landing.
Table 3. Machine rate assumptions (Black et al. 2025).
Variable Machine
Harvester Forwarder Tracked loader
Purchase price, USD 800 000 749 000 382 000
Salvage value, % of purchase price 29 29 41
Economic life, yr 6 7 6
Fuel consumption, l pmh–1 17.1 18.5 10.4
Lubrication, USD yr–1 7300 6800 6000
Maintenance and repair, USD yr–1 5500 4800 16 800
Utilization, % 69 77 71
Availability a, % 85 70 a 80
Scheduled machine hours (smh) yr–1 2000 2000 2000
l pmh–1 = liters per productive machine hour (excluding delays).
a Forwarder availability was increased to 85% when a tracked loader was added to the system to reflect that the forwarder operator no longer had to communicate with truck drivers and complete load tickets and other administrative responsibilities.
Table 4. Key performance indicators for the Ponsse Ergo harvester.
Variable Softwoods n = 436 Hardwoods n = 71 p-value
Mean SD Median Mean SD Median
Tree volume m3 0.627 0.496 0.500 0.229 0.303 0.160 <0.0001
Pieces per tree n° 3.0 1.0 3.0 1.7 0.8 2.0 <0.0001
Cycle time per tree s 62 51 49 52 53 33 0.0018
Productivity trees pmh–1 96 74 73 133 111 109 0.0018
Productivity m3 pmh–1 41.0 29.6 36.0 21.9 18.4 17.1 <0.0001
SD = Standard deviation; pmh = productive machine hours (excluding delays); m3 = cubic meters over bark; p-value returned by the non-parametric Mann-Whitney U-test.
Table 5. Regression equation for the Ponsse Ergo harvester cycle time.
Felling and processing time per tree (s)
s = a + b × tree volume (m3) + c × hardwood
R2 adjusted = 0.279, n = 507, RMS = 42.6
Coeff SE T P
a 26.8 3.2 8.294 <0.0001
b 55.6 4.0 13.905 <0.0001
c 11.1 5.7 1.954 0.0513
1

Fig. 1. Ponsse Ergo harvester cycle time (s tree–1) as a function of tree volume (m3) for both hardwood and softwood species.

Table 6. Key performance indicators for the Ponsse Elephant forwarder.
Variable Unit Mean SD Median
Outhaul s 552 151 532
Load s 793 289 727
Move s 206 179 119
Inhaul s 486 151 511
Unload onto deck s 337 130 298
Unload onto truck s 523 134 485
Distance m 631 223 622
Logs n° 54 9 52
Stops n° 4.6 1.9 4.0
Load m3 17.1 2.9 16.6
Productivity m3 pmh–1 25.7 6.1 26.8
Outhaul s m–1 0.88 0.22 0.90
Inhaul s m–1 0.76 0.28 0.79
SD = Standard deviation; pmh = productive machine hours (excluding delays); m3 = cubic meters over bark.
Table 7. Key performance indicators for loading with the Ponsse Elephant forwarder.
Variable Hot deck n = 14 Cold deck n = 3
Mean SD Median Mean SD Median p-value
Load log n° 88 13 90 85 9 88 0.5700
Load m3 27.8 1.8 27.5 28.9 2.9 29.7 0.6143
Loading time s 949 208 928 1330 42 1332 0.0233
Grapple loads n° 24 3 23 24 3 24 0.7984
Productivity m3 pmh–1 109.8 22.8 111.4 78.1 5.6 80.4 0.0233
Front n = 17 Rear n = 17
Mean SD Median Mean SD Median p-value
Load log n° 43 7 44 44 7 46 0.9241
Load m3 13.9 1.5 13.9 14.1 1.3 14.3 0.7946
Loading time s 470 131 477 546 135 523 0.0148
Grapple loads n° 11 2 11 12 2 12 0.1664
Productivity m3 pmh–1 114.2 33.6 104.0 98.3 26.0 99.2 0.0759
SD = Standard deviation; pmh = productive machine hours (excluding delays); m3 = cubic meters over bark; p-value returned by the non-parametric Mann-Whitney U-test.
Table 8. Individual machine and harvesting system productivity and cost of the observed system and two alternative scenarios.
Machine Harvester Forwarder System
Loading by forwarder
Delay-free function productivity (m3 pmh–1) 38.4 20.7  
System productivity (m3 smh–1)     14.5
System onboard truck cost ($ m–3) --   $15.91
System cut-and-haul cost ($ m–3) --   $23.93
  Loading by tracked loader
Delay-free function productivity (m3 pmh–1) 38.4 25.9  
System productivity (m3 smh–1)     22.2
System onboard truck cost ($ m–3)   $14.20
System cut-and-haul cost ($ m–3)   $22.21
  Loading setout trailers with forwarder
Delay-free function productivity (m3 pmh–1) 38.4 24.0  
System productivity (m3 smh–1)     19.2
System onboard truck cost ($ m–3)   $12.99
System cut-and-haul cost ($ m–3)   $21.00
pmh = productive machine hours (excluding delays); smh = scheduled machine hours (including delays); m3 = cubic meters over bark.