Logging residues quantities, and some properties of solid and finger-jointed lumber of stem (off-cuts) and branch wood of some Ghanaian tropical hardwoods

Abstract

The purpose of this study was four-fold: First, to estimate merchantable logging residues left in the forest after logging; second, to investigate the natural durability of stem and branch wood of five species; third, to compare the bending strength of solid and finger-jointed lumber; and finally to investigate the influence of anatomical properties on natural durability and mechanical properties of wood. The five wood species were Entandrophragma cylindricum (sapele), Entandrophragma angolense (edinam), Khaya ivorensis (mahogany), Terminalia superba (ofram), and Pterygota macrocarpa (koto/kyere). Forest residues were quantified with Smalian‟s equation, natural durability test was measured on percentage weight loss in accordance with EN 252-1989, whereas bending strengths of solid and finger-jointed lumber (produced with PVA adhesive) were evaluated in accordance with BS 373-1957, and the anatomical properties assessed using IAWA Committee protocol and using ImageJ software. Results showed 25% of merchantable logging residues of felled trees were left in the forest unextracted. Unlike branchwood of mahogany, ofram and koto whose natural durability were comparable to their stemwood, branchwood of sapele and edinam dried to 9±3%MC were significantly (p<0.05) better than their stemwood counterparts. Bending test showed significant (p<0.05) MOE differences from 9.4% to 23.5% higher in solid branchwood of edinam, mahogany and ofram, whereas MOR differences were from 16.5% to 23.5% higher in branchwood of edinam and mahogany compared to their stemwood counterparts with MC and wood type having significant effect (p=0.000). Branchwood finger-jointed lumber combinations produced joint efficiencies in MOE ranging from 59% to 110%, and those in MOR ranged from 30% to 68%. Expectedly, finger-joint efficiencies in MOE and MOR correlated inversely with wood density. But unlike the MOEs, MORs of all finger jointed combinations were significantly lower (p<0.05) than those of stemwood of their respective species. As a characteristic of hardwoods, sizes and quantities of some wood cells were either significantly (p<0.05) more or less in stemwood than in branchwood. As expected, fibre and parenchyma proportions respectively correlated inversely and positively with percentage weight loss. Also, fibre and vessel proportions correlated positively and inversely respectively with MOE and MOR. In conclusion, wood residues are of substantial quantities, and solid wood or finger jointed lumber of branches are not inferior to those of stemwood of the same species and therefore branches could be extracted for use to supplement stemwood so as to help in addressing the challenge being posed by timber shortages to industry and also help in reducing the depletion rate of Ghana‟s forest cover.