Forest structure and composition of previously selectively logged and non-logged montane forests at Mt. Kilimanjaro

Abstract

The montane forests of Mount Kilimanjaro in Tanzania have been subjected to a long history of selective logging. However, since 1984 logging of indigenous trees is prohibited. Today, these forests allow us to evaluate the long-term effects of selective logging. We mapped the height and diameter at breast height (DBH) of all trees >10cm DBH on 10 sites of 0.25ha. Five sites represent non-logged forests, another five selectively logged forests. We tested whether forests were still visibly affected 30–40years after selective logging in terms of their forest structure and tree diversity. Additionally we compared tree densities of different species guilds, including disturbance-indicator species, late-successional species and main timber species. Furthermore, we specifically compared the community size distributions of selectively logged and non-logged forests, first across all species and then for the most important timber species, Ocotea usambarensis, alone. 30–40years after selective logging forests still showed a higher overall stem density, mainly due to higher relative abundances of small trees (<50cm DBH) in general, and higher densities of small size class stems of late-successional species specifically. For O. usambarensis, the selectively logged sites harboured higher relative abundances of small trees and lower relative abundances of harvestable trees. The higher relative abundance of small O. usambarensis-stems in selectively logged forests appears promising for future forest recovery. Thus, outside protected areas, selective logging may be a sustainable management option if logging cycles are considerably longer than 40years, enough large source trees remain, and the recruiting O. usambarensis individuals find open space for their establishment.