Calibrating rotation age for eucalyptus pellita and eucalyptus grandis x urophylla to optimize market returns for transmission poles and plywood in Ghana

Thesis (MScFor)--Stellenbosch University, 2023.

ENGLISH ABSTRACT: There has been over-reliance on Tectona grandis and Ceiba pentandra for the manufacture of utility poles and plywood in Ghana. Miro Forestry has for the past eight years been growing various tree species including Eucalyptus pellita (Pellita) and E. grandis x urophylla (GU) on large- scale plantations for the first time in Ghana. However, optimum silvicultural regimes and growth and yield models are yet to be defined since the company is in its first full rotation. In this study, the determination of optimal rotation age for Pellita and GU for poles and plywood production was investigated. A combination of the market conditions, processing technology, silviculture regimes and Miro’s existing growth and yield functions were used to determine a suitable rotation age along with appropriate silvicultural treatments. Market analysis for pole size distribution and a plymill experimental study for peeler log processing were the benchmarks used to establish the optimum pole and peeler log specification to satisfy market demand and mill configuration. A taper function was used to calculate the tree size from which these logs can be produced. Once the optimal tree was ascertained, an investigation into the best regime to follow for poles and plywood ensued. This gave guidance on optimum silviculture regimes to grow the ideal tree for poles and plywood. Miro’s existing growth and yield functions within the Microforest software package were used to simulate different thinning scenarios to investigate growth response to thinning. Stocking, thinning intensity and frequency of thinning were altered to test their effect on the growth dynamics of the trees. Rotation age was defined by diameter growth and the time it took to reach the sizes of the optimum pole or peeler log. The results from this study showed that the optimum pole tree had a DBH of 23 cm and a height of 23.3 m. The optimum plywood tree had a DBH of 31 cm and a height of 30.8 m. The simulation results in Microforest showed that a two-thinning regime of 600 stems per hectare gave more favourable results and that GU would achieve diameters of 23 cm for poles at 8.5 years. Pellita would not be able to achieve those diameters even over a much longer rotation. Both species would not achieve the dimensions for an optimum plywood tree within the range of conditions tested. However, the plymill recovery for the smaller diameter class of 15-20 cm was not significantly different from the 20-30 cm class. A tree whose DBH is 21 cm and a height of 21.5 was also ideal for plywood and it produced logs whose average diameter fell within the 15-20 cm diameter class. A two-thinning regime would achieve these dimensions at six years for GU and 11 years for Pellita. GU had a biological and economic rotation of six and seven years respectively. The slower- growing Pellita had a biological rotation of 7.3 years, and the economic rotation was seven years. This study illustrates that when markets demand very specific product dimensions, the use of biological and economic rotation ages would be subservient to technical rotation age.

AFRIKAANSE OPSOMMING: In Ghana was te veel steun geplaas op Tectona grandis en Ceiba pentandra vir die vervaardiging van kragpale en laaghout. Miro Forestry het gedurende die laaste agt jaar verskeie spesies, insluitende Eucalyptus pellita (Pellita) and E. grandis x urophylla (GU) gekweek in grootskaalse plantasies in Ghana. Hulle optimale boskultuur regime en groeimodelle moet egter nog ontwikkel word omdat die maatskappy nou eers in ‘n eerste vol rotasie is. In hierdie studie is die optimale rotasie ouderdom vir Pellita en GU pale- en laaghout produksie ondersoek. ‘n Kombinasie van marktoestande, vervaardigingstegnologie, boskultuur regimes en Miro se bestaan groeifunksies is gebruik om ‘n geskikte rotasie ouderdom en toepaslike boskultuur behandelings te bepaal. ‘n Markontleding vir paal grooteverdeling en ‘n laaghout eksperimentele studie vir veneervervaardiging was gebruik as die maatstawwe vir die daarstelling van optimale paal en veneer blok spesifikasies, wat mark aanvraag en meule konfigurasies bevredig. ‘n Spitsingsfunksie is gebruik om die boomgroote te bepaal vanwaar optimale blok spesifikasies verkry kan word. Nadat die optimale boomgroote bepaal is, is die beste regime vir die kweek van so ‘n boom ondersoek. Dit het leiding gegee vir die bepaling van optimale boskultuur regimes vir die groei van die ideale boom vir pale en laaghout. Miro se bestaande groeifunksies in die Microforest sagtewarepakket is gebruik om verskillende dunningssenarios te simuleer om sodoende die groeieffek van dunnings te ondersoek. Stamtal, dunningsintensiteit en frekwensie van dunnings is verander om die effek op die groei van bome te toets. Rotasie ouderdom is gedefinieer deur deursneegroei en die tyd wat dit neem om die optimale paal en veneerblok grootes te bereik. Die resultate van die studie toon dat die optimale boom vir pale ‘n DBH van 23 cm en ‘n hoogste van 23.3 m moet he. Die optimale boom vir laaghout het ‘n DBH van 31 cm en ‘n hoogste van 30.8 m gehad. Die simulasie resultate van Microforest toon dat ‘n twee-dunning regime met 600 stamme per hektaar beter resultate lewer en dat GU die deursnee van 23 cm vir pale op die ouderdom van 8.5 jaar sal bereik. Pellita sal nie hierdie deursnee kan bereik nie, selfs oor ‘n veel langer rotasie. Beide spesies sal nie die afmetings vir die optimum laaghout boom kan bereik binne die reeks van toestande wat getoets is nie. Laaghout herwinning vir die kleiner blokklas van 15-20 cm was nie beduidend verskillend van die 20-30 cm blokklas. ‘n Boom met ‘n DBH van 21 cm en ‘n hoogste van 21.5 m was ook geskik vir laaghout en dit het blokke geproduseer binnedie gemiddelde deursneeklas van 15-20 cm. ‘n Twee-dunning regime sal hierdie boomdimensies kan bereik op ouderdom ses vir GU en ouderdom 11 vir Pellita.GU het ‘n biologiese en ekonomies rotasie van onderskeidelik ses en sewe jaar gehad. Die stadiger groeiende Pellita het ‘n biologiese rotasie van 7.3 jaar en ‘n ekonomiese rotasie van sewe jaar. Die studie illustreer dat as market baie spesifieke produkdimensies vereis, die gebruik van biologiese en ekonomiese rotasies ondergeskik is aan tegniese rotasie ouderdom.

Masters