Challenges, drivers and strategies for improving natural regeneration of African oak (<i> Afzelia</i><i> africana</i> Sm)

초록

African Oak ( Afzelia africana Sm. ex Pers.) is a keystone species with high socio-economic importance for local populations in tropical Africa. Yet, the long-term survival of the species in its natural habitats is uncertain given a lack of natural regeneration. Although substantial research has been conducted on this species, little consensus exists regarding best strategies to improve its growth and survival with respect to the regeneration challenges the species faces. This review provides a synthesis of the factors and processes underlying challenges to natural regeneration of A. africana and strategies to improve its regeneration. A total of 79 papers were amassed using RepOrting standards for Systematic Evidence Syntheses (ROSES). The findings indicated an increased interest in the topic over the last three decades, with most studies (84 %) being conducted in West Africa where conservation of the species is critical. The main regeneration challenges included low seedbank and seed germination rate, and lack of recruitment. Anthropogenic disturbances, drought, land-use change and conspecific adult density were the main causes of regeneration failure. The overexploitation of organs (leaves and stems) considerably reduces the species' fruit production, while drought is a major cause of seedling mortality. Studies used Janzen-Connell theory to explain the weak performance of seedlings in proximity to adults but this review suggests that the presence of a common mycelial network (CMN) may explain much of the observed negative dependence in conspecific density between adults and seedlings. Inoculation with mycorrhizal fungi in the genus Scleroderma and seed (mineral and organic) fertilization were effective in improving seedling growth. According to our findings, our understanding of the role that pathogenic fungi and intraspecific diversity play in the regeneration of the species is limited, calling for further research on these topics. Overall, our review highlights the need for environmental education of local communities on the importance of protecting the species natural regeneration together with the application of silvicultural measures at early growth stages to ensure long-term survival of African oak.

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