Abstract

The polycyclic selective logging system is the most widely applied system in tropical forests. Harvesting of logs from forests managed under pulycyclic systems is a significant silvicultural intervention. Selective logging is practiced in many natural forests of southwestern Ethiopia, but to date no studies have been undertaken. Therefore, the objectives of the work described in this thesis were (a) to study the effects of commercial selective logging on the residual stand; (b) to estimate the wood residue generated by selectively logging and sawmilling operations; (c) to assess the regeneration status in selective logged-over stands; (d) to study the growth and survival of commercial species using the enrichment planting method; and (e) to test the growth and photosynthesis responses of seedlings of commercial tree species to different light intensity. The studies were carried out in transitional rain forest in southwestern Ethiopia. On average for every tree felled, 8 trees above 5 cm in dbh were damaged during felling. The log recovery rate and lumber recovery factor were 38.3 and 36 %, respectively for selective logging and sawmilling operations. Saplings regeneration after two years was I745 ha⁻¹ and the number of poles after eight years was 263 ha⁻¹. The only commercial species considered having adequate natural regeneration was Cordia africana Lam. In the enrichment planting, the survival rate and mean height growth after 12 months varied from 50 to 100 % and 4.0 to 104.4 cm, respectively, depending on the species and treatment. A shading experiment showed that, except for the leaf number, there were no significant differences among treatments in collar diameter and height increment for seedlings of Aningeria adolfi-friederici (Engl.) Robyns & Gilbert but for C. africana seedlings there were significant differences in all cases. The average net photosynthesis for A. adolfi-friederici seedlings was highest for the seedlings grown at the lowest light treatment and for C. africana seedlings it was highest at the highest light treatment. The rain forests in southwestern Ethiopia probably can be managed effectively using selective logging methods. They have a potential to regenerate after such operations. However, currently they are exploited without any working plan. Therefore, the fate of these forests in the future depends on the efforts devoted now in putting them under sustainable management.