Recovery of forest biodiversity by natural ecological processes through native or alien tree stands.
Background and aims - Each natural forest area has species that function optimally in different development stages of that forest system. In forest rehabilitation we often plant mature forest species and ignore those species with adaptations to recover effectively after severe disturbance and degradation, and produce useful products at a fast rate. We clear stands of invasive alien species before we plant native tree species, all at great costs, to rehabilitate natural forest. By contrast, cost-effective commercial plantation forestry systems generally use fast-growing pioneer tree species introduced from other natural forest regions, which often facilitate the recovery of shade-tolerant native forest species. This paper provides a brief overview of how pioneer tree stands in different natural forest systems in Africa and Madagascar develop from monocultures to diverse mature forest communities. Methods - Three examples of natural forest pioneer tree stands are used to provide a brief overview of their development towards diverse mature forest: Virgilia divaricata after fire in South Africa, Musanga cecropioides after slash-and-burn agriculture in the Congo Basin, and Ravenala madagascariensis on the forest margin in southeastern Madagascar. Key results - Mono-specific pioneer stands on sites of degraded or cleared forest develop through different recovery stages, each with its own suite of species, towards mature, mixed-species forest. Several recovering species are important commercial timber species which do not regenerate in mature forest. Discussion - The results are compared with the parallel process of forest recovery through planted and naturalized species of invader trees (pines, eucalypts, acacias) and shrubs (Chromolaena odorata) as a basis for guidelines on rehabilitation of natural forest in an area. Conclusion - The process of forest recovery through planted and naturalized invader and native pioneer stands can be managed to rehabilitate natural forest biodiversity, processes and productive capacity without alien plant clearing or planting of native tree species while providing a source of income and manipulating the invader plant species out of the system.