In situ persistence of African wild olive and forest restoration in degraded semiarid savanna

Abstract

The ability to produce vegetative shoots is a form of persistence in arid and semiarid savannas allowing trees to survive herbivory, fire and cutting. In terms of growth rates and survival, this form of rejuvenation may be more successful than recruitment via seed rain or dormant seeds in the seed bank. For this reason, resprouting could play an important role in the tree canopy and forest microclimate recovery and forest succession. To assess whether coppice growth of African wild olive (Olea europaea ssp. cuspidata) should be considered for restoration of dry Afromontane forest, this study investigated olive coppice densities and characteristics in a 100-ha grazing exclosure in northern Ethiopia using random samples and systematic samples along transects. The response to pruning, expected to reactivate a leading shoot and thus contribute to faster tree habit and canopy recovery, was tested as a secondary objective. Olive coppice was more numerous than seedlings, especially along the natural drainage line of the landscape. While pruning yielded longer top shoots, it did not reactivate leading shoots. On the contrary, it triggered the formation of numerous long shoots on the pruning surface. Its high densities make olive coppice an interesting starting point for forest restoration, but due to its 'quantity-driven' coppicing strategy and tendency for lateral expansion, coppice management to reduce the number of shoots and to restore a tree habit in persistent Olea may be needed. To optimize the value of coppice in exclosures, further research on coppicing strategies and responses to various pruning techniques of both the pioneer and climax species is needed. © 2007 Elsevier Ltd. All rights reserved.