Patterns of common wood defects in some Ghanaian timber species
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Date
2003-11-23
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Abstract
Studies were conducted to assess defect status of some Ghanaian timber species in different forest zones and tree locations to establish wood defect patterns in the high forest zone of Ghana. Data were collected from the field records located in the archives of Timber Industry Development Division (T.I.D.D.) of the Forestry Commission of Ghana. Eighteen defects classified into shape, structural and deterioration were assessed for 40 species from off-reserve areas and 30 forest reserves for 5524 logs captured on the Log Measurement Conveyance Certificate (LAMCC) for the period of 1998 through 2001. Data were pooled for intraspecific comparison using various statistical procedures. Association among defects and log sizes were determined using Pearson’s correlation coefficient while differences among proportions of incidence of defects in different forest zones and tree locations, and association between defects and species were determined using chi-square test of proportion and independence. The study showed that every species exhibited at least a defect. Both low and high density, as well as durable and non-durable species of wood exhibited blemishes, which were dominated by natural defects; accordingly, there were no clean logs. The most prevalent defect was shakes, which constituted about 26% of total defects in the logs and were significant. The other common defects were identified to be irregular bole, buttresses, stain, heart-off- centre, bumps, splits, knots, decay heart and worm holes. Other defects which were relative/y rare ranged between 0.02 to 1.7%. A significant association was established between some species and defects, also incidences of defects in some species were influenced by the forest zone and tree location. The study established correlation between log size and incidence of defects in some species thus giving a partial credence to the size-associated defects assertion of the timber industry. In addition, natural defect category was associated with forest zones but not tree locations. Logs from the wet forest zone of Ghana were noted to be more susceptible to heart defects, buttresses, fluting, knots and stains among others. It was observed that timber species which are high/y priced were harvested irrespective of their forms and the high severity of shape defects reflected the state of the resources in the forest. The high incidence of preventable post harvest defects and fissures, pointed to a poor level of quality control measures in logging practices, which affect utility determination. There is therefore the need to manage factors influencing wood quality to conserve resources and to ensure quality products and efficiency to sustain employment levels and benefits accruing to the nation from timber.
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A thesis submitted to the Department of Materials Engineering in partial fulfilment of the requirements for the degree of Master of Science, 2003