Performance of preservative treatments on 32 timber tree species against termites and fungal attack at Bako, Southwestern Ethiopia

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 preservative treatablility (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 of field 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 for 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. Key words/phrases: Copper chromium arsenate, effectiveness of preservatives, natural durability, timbers, treatability