Silvicultural Systems for Restoration of Mahogany in Degraded Landscapes in Africa: Influence of Mixed Rainforest Plantation on Growth and Pest Damage

Abstract

African mahogany, one of the world’s most valuable timber species is threatened by over-exploita- tion in natural forests and failure of plantations due to attacks by the shoot borer Hypsipyla ro- busta. Mixed-species plantations has been reported to be an effective component of integrated pest management of major pest in other crops; but there is very limited empirical data on its use for managing Hypsipyla in mahogany mixed stands in West Africa. The aim of this study was to as- sess the effect of mixed-species stands as management intervention, on the growth of Khaya gran- difoliola and Khaya ivorensis in relation to Hypsipyla robusta attack in a 10 ha experimental plan- tation in the wet evergreen forest type in Ghana. Khaya grandifoliola recorded faster growth than Khaya ivorensis in this forest type though the later naturally grow in this forest type while the former is introduced from the dry forest. Two years after planting, diameter and height growth were greater in the mixed-species stand than the pure stands for K. grandifoliola and K. ivorensis. Hypsipyla damage was less in the mixed stands of both K. grandifoliola and K. ivorensis compared to the pure stands, with the 20% and 10% Khaya mixed stand recording the lowest attack in both species. It can be recommended that mixed stands of the two Khaya species at 20% or lower Khaya density might be ideal for reducing the levels of Hypsipyla attack in this type of forest.