Bergstrom, D.

Di Fulvio, F.

Nuutinen, Y.

Bergström, D.

Jukuri

Effects of harvested tree size and density of undergrowth on the operational efficiency of a bundle-harvester system in early fuel wood thinningsDan Bergström (SLU), Fulvio Di Fulvio (IIASA), Yrjö Nuutinen (Luke) Department of Forest Biomaterials and Technology, SLUdan.bergstrom@slu.seDemand for biomasses for biorefining will rise….-Use of bundle-harvesting systems for young dense thinningscould significantly reduce supply costs for small diameter trees (Bergström & Di Fulvio 2014, SJFR)….-A 3rd version of the Fixteri bundle-harvester has shown increases in efficiency of 90-160%. Bundles increases forwarders’ and trucks’ payloads by ca 50% (Björheden & Nuutinen 2014, Skogforsk report…). -System’s productivity has not been extensively studied in stands < 30 dm3, in which there may be significant proportions of disturbing under-growth trees (cf. Kärhä 2006 For. Stud.).Objectives• The objective of the study presented here was to evaluate effects of:a) harvested tree size b) and density of undergrowth on the operational efficiency of the third prototype of the bundle-harvester in early fuel wood thinnings. Study design• Scots pine dominated stands (by volume)• 26 harvesting units where inventoried• Time studies• Measures of:– bundle mass– MC– Thinning quality etc…• Analysis of time consumption, productivity….Stand characteristicsDBH basalStem volumeDensity Height Tot volumeDensity trees <2.5 cmStats (cm) (dm3) (trees/ha) (m) (m3/ha) (n/ha)Mean 8.0 26.5 5406 8.2 189.2 4523Min 6.3 15.0 2765 7.0 124.0 134Max 9.9 43.0 9302 9.7 302.0 11951Median 8.0 24.5 5200 8.1 173.5 3648SD 1.0 8.1 1583 0.7 48.7 3509- 8-wheeled Logman 811FC harwarder (Logman, Oy) - Logfit FT100 crane (Logfit AB), rotating cabin with endless turning. - Nisula 280E+ (Nisula Forest Oy) accumulating felling,  cutting diam. 28 cm.- Fixteri FX15a bundleing unit (mass ca. 6,500 kg, width 240 cm, length 410 cm, height  280 cm; www.fixteri.fi).The bundle-harvester systemMachine work sequenceA bundle2.6m length60-70 cm diam.0.45-0.5 m3Results: Work-efficiency >> no differences between treatments!StatsWork elementMean (sec/tree)SD (%) P-valueMove 0.8 0.2 7.4 0.661Fell 5.8 0.5 51.6 0.229Crut 1.5 0.4 13.2 0.902Crin 2.1 0.6 18.6 0.792Artr 0.1 0.1 1.1 0.901Arbu <0.1 0.1 0.2 0.240Bundle 0.5 0.3 4.5 0.848Drop 0.3 0.1 2.9 0.660Other 0.1 0.1 0.4 0.658Total 11.2 2.0 100 0.864Correlation between cutting and bundling work5250484644424038365,55,04,54,03,53,0Time consumption per crane cycle (sec)Time consumption per bundle (min)Productivity, mass30252015104,54,03,53,02,52,0Stem volume (dm3)Productivity (ODt/PMH)NO PCTPCTTreatmentProductivity, bundles302520151022201816141210Stem volume (dm3)Productivity (bundles/PMH)NO PCTPCTTreatmentDuring 98.5 PM15H: - 15.87 MWh of diesel fuel were consumed- 1392.36 MWh of biofuel were produced>>> average energy efficiency of 172 MJ/OD t (187 MJ/OD t in PM15time) and an EROEI of 80.6 (87.7 in PM15 time). (fuel consumption averaged 15.1 l/PM0H (16.4 l/PM15H))Average a bundle mass: 454 kg, fresh = 0.96 MWhAdditional test: Tree sections lost 37 kg (SD 29) mass during the bundling process=  7.1% of mass!  By visual inspection this mass consisted mainly of fine branches and needles. Conclusions- Unexpectedly, the density of undergrowth trees did not significantly affect the efficiency of the cutting work, as found in previous studies (e.g. Kärhä 2006, Jonsson 2015 MSc at SLU). - Accordingly, Jonsson (2015) found that defoliated undergrowth reduces visibility much less than fully leafed trees. - The undergrowth did not affect the quality of the thinning work either, which is consistent with the hypothesis that the undergrowth did not significantly impair visibility for the operator…. - Few of the harvested units in our study had dense spruce undergrowth, - which may be significant as spruce has greater branchiness than pine and birch (Kärhä (2006), and thus may have stronger effects….ConclusionsThe study provides information about the system’s performance that complements earlier findings, especially when handling relatively small trees! …additional explanation: - the cutting work in the present study was performed with an accumulating felling head equipped with shearing knives that is less sensitive to disturbing undergrowth during cutting than the accumulating harvester heads used in the cited studies. (Belbo, H. 2011. Efficiency of accumulating felling heads and harvesting heads in Mechanized thinning of small diameter trees. Doctoral Thesis. Linnaeus Universitetet.)-Simple, robust och unsensitive for undergrowth, stones…!(but rel. slow!) The bundling unit’s maximum efficiency was not reached during the trial, but estimates indicate that it could be significantly (perhaps up to 100%) higher. - However, to reach such efficiency the system would have to be equipped with a felling and bunching head that can cut and accumulate trees during continuous boom movements. + +Boom-corridor thinning methodsNew cutting technologyIntegrated bundlingNext step(s)….Prototypes!- MAMA-head+ =- ”Flowcut”![Forest Engineers Raul Fernandez Lacruz and Mikael Öhman are acknowledged for helping out with the field work.]• Thanks, Dan, Fulvio and Yrjö!• dan.bergstrom@slu.se

Effects of harvested tree size and density of undergrowth on the operational efficiency of a bundle-harvester system in early fuel wood thinnings

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