Density, some anatomical properties and natural durability of stem and branch wood of two tropical hardwood species for ground applications

摘要

As wood resources deplete, branchwood is being promoted to supplement stemwood in Ghana, but its natural durability, which indicates its service life and can influence its acceptance and use is scarcely studied. This study compares the natural durability and some anatomical properties of branchwood and stemwood of Entandrophragma cylindricum (sapele) and Khaya ivorensis (mahogany) using Ceiba pentandra stemwood as control. Natural durability test followed field test method according to European Standard EN 252 1989 in combination with percentage weight losses while the anatomical investigations followed IAWA Committee 1989 recommendations. For each species, two branch logs were cut from each of two sampled trees from two natural forests in Ghana. Stemwood was also obtained from the same forest reserves as the branches. All sample groups were tested at air-dried moisture content of 14 +/- A 2 as specified in the standard. Branchwood of both species were denser than their stemwood, but in addition to mahogany stemwood they were rated "non-durable", while sapele stemwood was rated moderately durable. Thus at 5 significance level, natural durability of mahogany branchwood appeared comparable to that of its stemwood whereas sapele branchwood was significantly less durable than its stemwood but more durable than Ceiba stemwood. Branchwood and stemwood vessels diameter and proportion also were significantly different (p < 0.1). Expectedly, density correlated positively with natural durability, but the correlation among anatomical properties, natural durability and density were stronger in stemwood than in branchwood. In conclusion, stem and branchwood of mahogany are both non-durable but sapele stemwood appears better than its branchwood for ground applications. Anatomical properties of stemwood influenced natural durability more than those of branchwood. For better acceptance of branchwood of the species for wood products manufacturing, further research would be necessary for additional data on their toxic extractive levels, mechanical properties and durability at different sites or/and using other drying methods.