L’or vert du Gabon : une synthèse bibliographique de trente années de recherche sur l’okoumé (Aucoumea klaineana Pierre)

peer reviewedIntroduction. Aucoumea klaineana Pierre is the most harvested timber species in Central Africa and plays a key role in the economy of Gabon. This tree is considered “Vulnerable” for more than three decades by the IUCN because its population is assumed to have been reduced by at least 50% as a result of logging. The objective of this review is to synthesize recent and relevant knowledge in order to update this status. It focuses more specifically on ecology, population dynamics, silviculture and impacts of logging. Literature. Its natural range mainly covers Gabon. It is a light-demanding and gregarious species that forms root anastomoses. It principally establishes itself in abandoned fields and savannahs. In mature forest its regeneration is rare and limited to large gaps. Selective logging only allows significant regeneration along roads. However, at the scale of Gabon, the species is abundant and its renewal is ensured. Legal logging does not threaten the species. However, after decades of logging focusing on best shaped trees, a production of lower quality is feared. The implementation of a thoughtful silviculture could be a solution. Conclusions. Aucoumea klaineana is not vulnerable under IUCN A1 criterion. However, the maintenance of a high-quality production over the long term calls for the implementation of silviculture based on a thorough knowledge of the factors affecting stand dynamics, especially the role of the rhizosphere. Although long described, the functioning of root anastomoses has never been studied in depth.Introduction. Aucoumea klaineana Pierre est l’essence de production la plus exploitée d’Afrique centrale et elle joue un rôle fondamental dans l’économie du Gabon. Elle est considérée comme « Vulnérable » depuis plus de trois décennies par l’UICN car sa population est supposée avoir été réduite d’au moins 50 % à cause de l’exploitation forestière. L’objectif de cette revue est de synthétiser les connaissances récentes et pertinentes afin d’actualiser ce statut. Elle se concentre plus particulièrement sur l’écologie, la dynamique des populations, la sylviculture et les impacts de l’exploitation forestière. Littérature. Il s’agit d’une espèce quasi endémique au Gabon. Elle est héliophile, grégaire et forme des anastomoses racinaires. Elle se régénère principalement dans les champs abandonnés et les savanes. Sa régénération en forêt mature est rare et limitée aux trouées de grande dimension. L’exploitation forestière sélective ne permet une régénération significative que le long des routes. Toutefois, à l’échelle du Gabon, l’espèce est abondante et sa régénération assurée. L’exploitation forestière, si elle respecte les normes légales, ne menace pas l’espèce. Cependant, s’étant focalisée pendant des décennies sur les plus beaux pieds, une production de moindre qualité est redoutée. La mise en œuvre de plantations et d’autres méthodes de régénération pourraient y remédier. Conclusions. Aucoumea klaineana n’est pas une espèce vulnérable selon le critère A1 de l’UICN. Néanmoins, le maintien d’une production de qualité sur le long terme nécessite la mise en place d’une sylviculture basée sur une connaissance approfondie des facteurs affectant la dynamique des peuplements, notamment le rôle de la rhizosphère. Bien que des anastomoses racinaires aient été décrites depuis longtemps, leur fonctionnement n’a jamais été étudié

Gabon's green gold: a bibliographical review of thirty years of research on okoume (Aucoumea klaineana Pierre)

Introduction. Aucoumea klaineana Pierre is the most harvested timber species in Central Africa and plays a key role in the economy of Gabon. This tree is considered “Vulnerable” for more than three decades by the IUCN because its population is assumed to have been reduced by at least 50% as a result of logging. The objective of this review is to synthesize recent and relevant knowledge in order to update this status. It focuses more specifically on ecology, population dynamics, silviculture and impacts of logging. Literature. Its natural range mainly covers Gabon. It is a light-demanding and gregarious species that forms root anastomoses. It principally establishes itself in abandoned fields and savannahs. In mature forest its regeneration is rare and limited to large gaps. Selective logging only allows significant regeneration along roads. However, at the scale of Gabon, the species is abundant and its renewal is ensured. Legal logging does not threaten the species. However, after decades of logging focusing on best shaped trees, a production of lower quality is feared. The implementation of a thoughtful silviculture could be a solution. Conclusions. Aucoumea klaineana is not vulnerable under IUCN A1 criterion. However, the maintenance of a high-quality production over the long term calls for the implementation of silviculture based on a thorough knowledge of the factors affecting stand dynamics, especially the role of the rhizosphere. Although long described, the functioning of root anastomoses has never been studied in depth

Disentangling the ecology of Aucoumea klaineana Pierre to improve its sustainable management

12. Responsible consumption and productio

Unraveling Belowground Interactions in Okoumé (Aucoumea klaineana Pierre) stands: the roles of Root Anastomoses and Mycorrhizal Associations

Okoumé (Aucoumea klaineana Pierre) is the most harvested timber species in Central Africa. This pioneering light-demanding species favors open environments to form monospecific stands. During forest management activities, thinning operations in these stands were carried out. Through subsequent operations, the stumps of felled trees were discovered to be alive. Their survival was found to be assisted by the graft (anastomose) of their root steles with close conspecifics reaching the canopy. This enabled hydromineral and carbon exchanges between individuals and extension of the root system of canopy trees. Despite the widespread occurrence of root anastomose among woody species, physiological mechanisms involved and their importance are poorly understood. For the first time in the tropics, we investigated it in young interconnected natural stands. We clearcut and excavated three stands using fire hose to expose roots. Cross-sections of stems, roots, and root grafts were collected to observe growth rings patterns. The impact of root grafts on suppressed trees survival and tree growth through dendrochronology was then analyzed. Preliminary findings show the presence of shared growth rings within root grafts, proving exchanges between individuals. Knowing that mycorrhizal associations are key components of tropical forests, the belowground interactions among A. klaineana trees are unlikely to be exclusively the result of root anastomoses. For that reason, we also investigated the mycorrhizal status of the species to gain understanding of these interactions influence their growth, health, and ecological roles. By collecting fine roots, we aimed to elucidate the links between fungal communities (through specific richness and functional diversity) and growth dynamics across populations of varying ages and structures through metabarcoding methods. Among 4.818 OTU, preliminary results show a low pathotroph (4%) but high saprotroph load (36%) compared to symbiotrophic fungi (26%, of which 80% of arbuscular mycorrhizal fungi, AMF), 34% uncertain. Considering two belowground flows, we shed light on the relative importance of AMF in fungal assemblages in A. klaineana populations and could reveal the impact of root anastomoses on variations in tree growth. This contributes to fill knowledge gaps regarding A. klaineana ecology and interactions at the stand scale to improve management strategies by finding a balance between productivity and sustainable resource us

Disentangling the ecology of Aucoumea klaineana Pierre to improve its sustainable management

12. Responsible consumption and productio