Evaluation of a mechanized CTL harvesting system in different geometric thinning operations in terms of productivity, cost, biomass conversion, residual stand damage and spacing uniformity

Thesis (MScFor)--Stellenbosch University, 2021.ENGLISH ABSTRACT: This study was aimed at comparing conventional 7th row thinning with diagonal thinning in terms of productivity, cost, biomass conversion efficiency, residual stand damage and spacing uniformity. The study was based on two adjacent Pinus patula compartments on the Mpumalanga Highveld. A time study was conducted to test time consumption and productivity of both harvesting and forwarding between the two treatments. Residual tree damages were assessed by inspecting all individual trees within research plots for any woundings. Cost calculations were carried out on each machine per thinning treatment to determine which machine was more cost-effective. Voronoi polygons and simulations were used to determine spacing uniformity and biomass conversion efficiency was tested by enumerating woody residues that were above the commercial limit diameter remaining in the stand after timber extraction. iii Summary This study was aimed at comparing conventional 7th row thinning with diagonal thinning in terms of productivity, cost, biomass conversion efficiency, residual stand damage and spacing uniformity. The study was based on two adjacent Pinus patula compartments on the Mpumalanga Highveld. A time study was conducted to test time consumption and productivity of both harvesting and forwarding between the two treatments. Residual tree damages were assessed by inspecting all individual trees within research plots for any woundings. Cost calculations were carried out on each machine per thinning treatment to determine which machine was more cost-effective. Voronoi polygons and simulations were used to determine spacing uniformity and biomass conversion efficiency was tested by enumerating woody residues that were above the commercial limit diameter remaining in the stand after timber extraction. Harvesting results showed a significant difference between the two treatments at (p < 0.05). Conventional 7th row thinning had the highest mean productivity at 16.49 m3/PMH compared to 14.36 m3/PMH for diagonal thinning. Forwarding results also showed a significant difference between the two treatments at (p < 0.05). Diagonal thinning had a mean productivity of 4.61 m3/PMH compared to 5.36 m3/PMH for the conventional 7th row thinning. The conventional 7th row thinning method had the lowest cost of R273.93/ m3 compared to R324.28/ m3 for diagonal thinning. Residual tree damages showed a significant difference between the two treatments at (p < 0.05). Diagonal thinning had an average residual tree damage of 8.9% compared to 4.4%. The diagonal thinning method had the highest fibre losses at 12.65 m3/ha and 10.52 m3/ha for conventional 7th row thinning. There was a significant difference between the two treatments. The study showed that conventional 7th row thinning is a better method in terms of productivity, cost and residual tree damages. Diagonal thinning, however, proved to be better in terms of thinning quality with regards to improving spacing uniformity and improving size distributions.AFRIKAANSE OPSOMMING: Die hoof doel van die studie was om konvensionele ry dunning met diagonale dunning te vergelyk wat betref ontginnings produktiwiteit, koste, doeltreffendheid van biomassa omskakeling, boomskade en die uiteindelike eenvormigheid van oorblywende boom spasiëring in die vak. Die studie was gebaseer op twee aangrensende Pinus patula vakke op die hoëveld van Mpumalanga. ʼn Tydstudie is uitgevoer om tydsverbruik en produktiwiteit van die ontginnings proses tussen die twee dunnings metodes te vergelyk. Oorblywende boomskade is ook ondersoek vir die twee metodes deur fisiese meetings. Kosteberekeninge is op elke masjien wat in elke dunning metode gebruik is uitgevoer. ʼn Voronoi-veelhoeke metodiek en simulasie berekeninge is gebruik om die eenvormigheid van finale boom spasiëring te bepaal. Doeltreffendheid van biomassa herwinning is getoets deur die oorblywende hout vesel, na ontginning, te bepaal deur fisiese metings. Finale resultate toon 'n beduidende verskil tussen die twee behandelings (p < 0.05) vir vel en blok voorbereiding. Vir vel en blok voorbereiding het die sewende ry konvensionele dunning die hoogste gemiddelde produktiwiteit vertoon (16.49 m3/PMH) in vergelyking met 14.36 m3/PMH vir diagonale dunning. Met hout uitsleep was daar ook 'n beduidende verskil tussen die twee behandelings (p < 0.05). Diagonale dunning het 'n gemiddelde produktiwiteit van 4.61 m3/PMH getoon in vergelyking met 5.36 m3/PMH vir konvensionele ry dunning. Konvensionele 7de ry dunning metode was die goedkoopste teen R273.93/m3 in vergelyking met R311.53/ m3 vir diagonale dunning. Daar was ook ʼn beduidende verskil wat betref oorblywende boom skade tussen die twee behandelinge (p < 0.05). Vir diagonale dunning was die gemiddelde 8.9% in vergelyking met 4.4% vir die konvensionele metode. Die diagonale dunnings metode het ook die grootste vesel verliese vertoon met 12.65 m3/ha in verlyking met 10.52 m3/ha vir die konvensionele metode. Die studie het getoon dat konvensionele 7de ry dunning die verkieslikste hout ontginning metode bly in terme van produktiwiteit, koste en uiteindelike boom skade. Diagonale dunning was egter beter ten opsigte van dunning kwaliteit en die verbetering van eenvormigheid van uiteindelike boom spasiëring en grootte verspreiding na dunning.Master