PERFORMANCE OF PRESERVATIVE TREATMENTS ON 32 TIMBER TREE SPECIES AGAINST TERMITES AND FUNGAL ATTACK AT BAKO, SOUTHWESTERN ETHIOPIA

Abstract

In Ethiopia, wood damage in construction and furniture sectors caused by biodegrading
agents is economically important. Experiments were carried out on 32 timber species to study
preservativetreatabWity (laboratory test) and natural durability of construction timbers, and
effectiveness of preservatives against subterranean termites and fungal deterioration at Bako. Antaris
toxicaria (681.14 and 20.43 kg m·3) and Eucalyptus camaldulensis (37.33 and 1.12 kg m·3) indicate the
highest and the lowest chemical absorption and retention properties, respectively. A. toxicaria (25 mm)
and Fagaropsis angolensis (1.5 mm) had the highest and lowest chemical penetration, respectively.
Significant differences (p < 0.01) were found in the absorption, retention and permeability of Copper
Chromium Arsenate (CCA) among the timbers. In the damages caused by termites and fungi, significant
differences (p < 0.01) were also found between stakes treated with CCA and the controls among the
study species and field exposure times, and in the interactions between preservatives and study species
as well as preservatives and field exposure times. The extent of attack varied with species,
preservatives, application methods and length offield exposure periods. The majority of stakes (> 62%)
treated with CCA by pressure method resisted degradation by termite and fungi for more than 11 years,
those treated with used motor oil fOl;more than five years and the untreated stakes for one to four
years. Therefore, timbers from matured trees should be selected and rationally utilized for furniture
and construction purposes with appropriate protection measures taking into account
place! environment of use, the costs of preservation, the service life of each timber species and the
service life intended.