Industrial forestry compartment characteristics: the effect on end of rotation processes and the forestry supply chain

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dc.contributor.advisorTalbot, Bruceen_ZA
dc.contributor.advisorAstrup, Rasmusen_ZA
dc.contributor.authorAckerman, Simon Alexanderen_ZA
dc.contributor.otherStellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.en_ZA
dc.date.accessioned2022-03-11T09:55:32Zen_ZA
dc.date.accessioned2022-04-29T12:56:07Zen_ZA
dc.date.available2023-03-18T03:00:08Zen_ZA
dc.date.issued2022-03en_ZA
dc.descriptionThesis (PhD)--Stellenbosch University, 2022.en_ZA
dc.description.abstractENGLISH ABSTRACT: Industrial plantation management aims to produce timber at the end of its rotation of a desired size to maximise the volume on the site, through the application of intensive silviculture. These silvicultural operations maximise this volume primarily through maintaining an acceptable level of tree size and tree size distribution uniformity. With tree size strongly related to timber harvesting productivity, uniformity of the trees on the stand should also benefit these end of rotation processes. For this reason, a series of experiments were undertaken to test the effect of tree size uniformity of mechanised cut to length (CTL) harvesting. These were firstly, to understand the fine scale effect of tree-by-tree mechanised CTL harvesting productivity and overall costs and cost sensitivity for two different sized harvesting machines (medium sized Ponsse Beaver and larger Ponsse Bear). Secondly, to explore the consequences of varying tree distributions on the productivity of mechanised CTL harvesters by comparing the marginal and weighted mean productivity at clear-felling age. Lastly, to investigate the systems effect of mechanised CTL harvesting of marginal first thinning trees by a combination harvester-forwarder machine in a fully selective thinning operation. In the first investigation, a long-term data set of harvesting machine data were collected and analysed using a non-linear mixed effects modelling approach to model the productivity for each of the different sized machines applied to the machine-based tree data. Results showed clear differences between the productivity of these two machine sizes and a clear decline of productivity when these machines reached their technical tree size limit. In terms of machine costs, the higher capital cost machine, the Bear, was only slightly greater to that of the Beaver. This was due to the high productivity of the Bear in the tree sizes harvested by this machine. Cost sensitivity further reinforced this; with the Bear’s capital cost being offset by the machine’s productivity, even at high interest rates. This investigation showed that both machines could effectively operate in any tree size, although one could infer that the smaller machine is not technically suited to large trees, and these could damage the machine in the long term. The second investigation used the models and data from the first investigation and compared these marginal productivity results to a weighted mean productivity when using the tree distribution rather than assuming a uniform distribution of trees in a stand. This investigation showed the disparity between using a mean tree size to predict harvesting productivity vs the tree size distribution. This disparity equates up to 8 m3 PMH-1 for the smaller Ponsse Beaver. This component highlights where remote sensing technology can be used to measure stand tree distributions more accurately than current enumeration techniques. The third part of the study investigated the application of a small-scale combination harvester forwarder in small and poor form first thinning trees. The investigation highlighted the challenges faced with these small and poorly formed trees that often the standing tree volume is not effectively translated to timber extracted to roadside. This necessitated a quantification of this timber ‘waste’ and an adjustment of the harvesting component’s productivity to take this into account. Further to this, since the machine forms a harvesting and forwarding system (the harvesting and forwarding functions cannot operate at the same time), the systems productivity was calculated, with the overall productivity limited by the least productive function. This final experiment aligned the previous two, where heterogeneous tree size effect of CTL harvesting is quantified. The overall objectives of the study were met, and it was found that tree size uniformity does affect CTL harvesting productivity. To this end, this needs to be matched against investments in more intensive silviculture. The study also highlighted the connection with the need for accurate stand characterisation to efficiently predict tree metrics for efficient timber harvesting.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Lineêre lae-digtheid poliëtileen (LLDPE) word gereeld in die solveerproses vervaardig via die kopolimerisering van etileen en α-olefiene in ’n onaktiewe koolwaterstof verdunner. Die etileen, α-olefiene en verdunner vorm gesamentlik die oplosmiddel waarin die vervaardigde LLDPE opgelos is. Doeltreffende bedryf van die solveerproses vereis egter gedetailleerde kennis van die (oplosmiddel + LLDPE) fasegedrag. Eksperimentele meting is die mees betroubare wyse waarop hierdie fasegedrag bepaal kan word, maar metings van polimeersisteme is ingewikkeld en tydrowend. Hierdie ondersoek het dit daarom daar gestel om die voorspellings van (oplosmiddel + LLDPE) sisteme se fasegrense vanaf ’n eksperimentele, teoretiese en fenomenologiese perspektief te verbeter. Vir die eksperimentele gedeelte van hierdie studie is damp–vloeistof (VL), vloeistof–vloeistof (LL) en damp–vloeistof–vloeistof (VLL) fasegrense van (etileen + komonomeer + n-heksaan + LLDPE) sisteme gemeet met ’n sinteties-visuele hoëdruksel. Die komonomere 1-buteen, 4-metiel-1-penteen, 1-hekseen, 1-okteen en 1-dekeen is ondersoek. Alle metings is uitgevoer met ’n metalloseen etileen/1-hekseen kopolimeer (𝑀̅w=199 kg·mol−1, 2.6 mol% 1-hekseen, 𝑀̅w𝑀̅n⁄=2.6) van industriële oorsprong. Die eksperimentele werk is in twee dele uitgevoer. Eerstens is die uitwerking van α-olefien-lengte en -konsentrasie in (α-olefien + n-heksaan + LLDPE) sisteme bepaal vir die C2 tot C10 lineêre α-olefiene. Dit het gewys dat die fase-oorgangsdrukke: (i) lineêr varieer met die polimeervrye olefienfraksie; (ii) toeneem vir die C2 tot C6 α-olefiene; en (iii) afneem vir die C8 tot C10 α-olefiene. Hierdie waarnemings kan verduidelik word in die konteks van die semi-additiewe aard van die polimeer–α-olefien dispersiekragte. Etileen veroorsaak ook ’n beduidende antisolvensie effek op die oorgangsdrukke wat waarskynlik gebeur as gevolg van π-elektronafstoting. ’n Tweede eksperimentele ondersoek het die gemiddelde oplosmiddel-eienskappe met (oplosmiddel + LLDPE) fasegrense in verband gebring aangesien dit nie uitvoerbaar is om (etileen + komonomeer + n-heksaan + LLDPE) fasegrense te meet vir alle moontlike oplosmiddel-samestellings nie. Dit is vir alle sisteme bevind dat etileen–komonomeer interaksies weglaatbaar is, en dat die laer kritiese eindpunt (LCEP) temperature sterk gekorreleer is met die gemiddelde oplosmiddel-molmassa. Dit is ook gewys dat die bestaande dighteidskorrelasies nie daartoe in staat is om fasegedragvoorspellings te maak vir sisteme wat C6 of swaarder α-olefiene bevat nie, omdat die oplosmiddeldigtheid nie verband hou met die oplosmiddel se vrye volume nie. Vir die teoretiese gedeelte van die werk is ’n sistematiese ondersoek geloods om die voorspellingsvermoëns van die geperturbeerde-ketting statistiese assosiërende vloeierteorie (PC-SAFT) te bepaal. Elkeen van die faktore wat (oplosmiddel + LLDPE) fasegrense beïnvloed, is oorweeg en twee verskillende vertakkingskonsepte is vergelyk [Gross et al. Ind. Eng. Chem. Res. 42, 1266; Dominik & Chapman Polymer 38, 10836]. Die uitwerking van binêre interaksieparameters (BIPs) wat deur groepsbydrametodes (GCMs) [Peters et al. Fluid Phase Equilib. 358, 137] afgeskat is, is ook ondersoek. Dominik en Chapman se vertakkingskonsep het effens beter resultate tot gevolg gehad, en verdere verbeterings kan verkry word deur die GCM-afgeskatte BIPs te gebruik. ’n Vereenvoudigde BIP-afskattingsmetode is daarna ontwikkel vir Dominik en Chapman se vertakkingskonsep, wat gelei het tot ’n effense verbetering in die voorspellingsvermoëns van solveerprosesstelsels en eenvoudiger korrelasie van multi-komponentsisteme. Die werk het uiteindelik gelei tot ’n nuwe drie-parameter ooreenstemmende toestands-teorie (CST) spesifiek vir (oplosmiddel + LLDPE) sisteme. Hierdie teorie is op drie postulate gebaseer: (i) die VL, VLL, en LL fasegrense van (oplosmiddel + poliölefien) sisteme, gereduseer rondom die LCEP, val saam op ’n universele stel fasegrense wat vanaf die Clapeyron vergelyking afgelei kan word; (ii) die LCEP-temperature van (oplosmiddel + poliölefien) sisteme vertoon dieselfde sensitiwiteit tot oplosmiddel-molmassa; en (iii) die LCEP-drukke kan benader word as die borrelpuntdrukke van die polimeervrye oplosmiddel. Die CST vorm dan die basis van ’n fenomenologiese metode waarmee die fasegrense van (oplosmiddel + LLDPE) sisteme voorspel kan word. Die metode benodig as intreeveranderlikes slegs algemene eienskappe van die oplosmiddel en ’n enkele troebelpuntdruk van ’n (oplosmiddel + LLDPE) sisteem met ’n soortgelyke polimeer, maar enige oplosmiddel. Die volledige VL, VLL en LL grense kan dan vir enige sisteem oor die benodigde temperatuurreeks afgeskat word. Hierdie studie maak dus wetenskaplike bydraes in die vorms van (i) nuwe eksperimentele metings wat die rol van opgeloste α-olefiene in (oplosmiddel + LLDPE) sisteme vasstel, (ii) vereenvoudigde en verbeterde voorspellings van (oplosmiddel + LLDPE) fasegrense in die PC-SAFT-raamwerk en (iii) ’n vinnige en eenvoudige metode waarmee (oplosmiddel + LLDPE) fasegrense aanlyn voorspel kan word. Gevolglik verbeter hierdie ondersoek die voorspellings van (oplosmiddel + LLDPE) fasegrense wat tot die solveerproses relevant is.af_ZA
dc.description.versionDoctoralen_ZA
dc.embargo.terms2023-02-28en_ZA
dc.format.extentxi, 71 pages : illustrationsen_ZA
dc.identifier.urihttp://hdl.handle.net/10019.1/125149en_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subject.lcshForests and forestry -- Supply and demanden_ZA
dc.subject.lcshForest productivityen_ZA
dc.subject.lcshHarvesting machineryen_ZA
dc.subject.lcshUCTDen_ZA
dc.titleIndustrial forestry compartment characteristics: the effect on end of rotation processes and the forestry supply chainen_ZA
dc.typeThesisen_ZA
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