Management of African economic trees for new research, the review of Entandrophragma genus (Meliaceae)

Entandrophragma genus includes exclusively African species (10 to 12), five of which are on the IUCN Red List. Characterized by a taxonomic evolution that has resulted in an important synonymy of species names (36-3 7) and insufficient ecological knowledge, it is the richest in valuable species exploited as timber in Africa. This important exploitation is likely to compromise their durability in the absence of sustainable management. Our study is mainly based on scientific data (e.g., publications), economic data (production and export statistics) and legal data (laws and regulations); on management plans and inventory reports. The heavy industrial exploitation as artisanal does not always proceed in the respect of a validated management plan, nor of the duration of the rotations which would make it possible to reach a rate of reconstitution likely to perpetuate the resource which these species represent. Their sustainable management requires the development and respect of management measures to make their exploitation sustainable in the long term. This exploitation must be based on an adequate management of natural stands and on reforestation as well as on conservation measures. The research to be developed must focus on their growth rate (eg, in the face of climate change), the analysis of stable rings and isotopes, the evaluation of their stocks (production, biomass, carbon), their spatial distribution and molecular phylogeny, the improvement of their natural regeneration, their reproduction, phenology and anatomy, as well as the reinforcement of other relevant lines of research to guarantee the durability of these forest species

Pith-to-bark profiles of xylem vessel traits reveal unique information on tree performance in a tropical moist semi-deciduous forest of the Congo Basin

Xylem vessel features are the most investigated anatomical traits of Angiosperm wood. They are being analyzed in ecophysiological projects aiming at understanding sap flow and vulnerability to drought stress. Since long, size, grouping and density of vessels are also used as one of the first steps in timber identification, as they can easily be observed even with a hand lens. Vessels are also known to be related to tree height. The volumetric sap flow rate is inversely related to the length of the path, so that vessels need to widen at lower parts of the tree and taper towards the higher parts to assure optimal transport and a stable hydraulic resistance with progressing growth in height. Vessels are expected to narrow from roots to stem and further to the branches and the petioles. Accordingly it is also predictable that vessel features on pith-to-bark profiles are a proxy for height growth for individual trees. Since the functional groups of species of a tropical rainforest are based on height grow rate (related to light needs), it is expected that pith-to-bark profiles of vessels reveal information on temperament of the species. A methodology has been developed to establish pith-to-bark profiles of vessel features, based on long microtomic sections, image analysis and machine learning. Entandrophragma was used as a model genus. The differences between the four most common species of this genus have been explored. Wilcoxon signed rank test indicate that the difference in mean vessel size is significant between every species combination except between Entandrophragma candollei and Entandrophragma cylindricum. Interesting to note is the large vessel size range possible for Entandrophragma utile. Currently, pith-to-bark vessel trends are constructed that could help explaining difference in growth strategy. The approach offers appealing perspectives to find a formal way for sub setting tree species into functional groups and develop indexes for growing conditions of forest sites

Enjeux et amélioration de la gestion des espèces du genre Entandrophragma, arbres africains devenus vulnérables

Because of the quality of their wood and their many traditional uses, species of the Entandrophragma genus are being intensively logged, and this is likely to compromise their survival unless sustainable management is introduced. This study reviews the current status of the five main commercial Entandrophragma species: Entandrophragma angolense, E. congolense (often confused with E. angolense), E. candollei, E. cylindricum and E. utile. We suggest directions for research to improve sustainable management strategies for this genus. The study draws mainly on published scientific data, economic data (production and export statistics) and on relevant laws and regulations, but also on existing management plans and inventory reports. Although these species are reported as vulnerable on the IUCN Red List, knowledge on their management is still patchy. Industrial and artisanal logging is intensive and does not always follow a validated management plan or abide by the minimum rotation period, both of which would help to ensure the renewal of these resources. Managing them to ensure that logging is sustainable in the long term requires management measures to be developed and complied with. Sustainable use has to be based on appropriate management of natural stands and on reforestation and conservation measures. Research studies to be developed should encompass the growth rates of the species in the light of the changing climate, assessments of stocks (timber, biomass and carbon), updates of their spatial distribution, improvements to natural regeneration, reproduction processes and the anatomical and technical properties of each species. All these research topics are necessary to ensure the permanence of these Entandrophragma species

Enjeux et amélioration de la gestion des espèces du genre Entandrophragma, arbres africains devenus vulnérables

Because of the quality of their wood and their many traditional uses, species of the Entandrophragma genus are being intensively logged, and this is likely to compromise their survival unless sustainable management is introduced. This study reviews the current status of the five main commercial Entandrophragma species: Entandrophragma angolense, E. congolense (often confused with E. angolense), E. candollei, E. cylindricum and E. utile. We suggest directions for research to improve sustainable management strategies for this genus. The study draws mainly on published scientific data, economic data (production and export statistics) and on relevant laws and regulations, but also on existing management plans and inventory reports. Although these species are reported as vulnerable on the IUCN Red List, knowledge on their management is still patchy. Industrial and artisanal logging is intensive and does not always follow a validated management plan or abide by the minimum rotation period, both of which would help to ensure the renewal of these resources. Managing them to ensure that logging is sustainable in the long term requires management measures to be developed and complied with. Sustainable use has to be based on appropriate management of natural stands and on reforestation and conservation measures. Research studies to be developed should encompass the growth rates of the species in the light of the changing climate, assessments of stocks (timber, biomass and carbon), updates of their spatial distribution, improvements to natural regeneration, reproduction processes and the anatomical and technical properties of each species. All these research topics are necessary to ensure the permanence of these Entandrophragma species

Le genre Entandrophragma (Meliaceae) : taxonomie et écologie d'arbres africains d'intérêt économique (synthèse bibliographique)

Introduction. Les espèces d'arbres du genre Entandrophragma font l'objet d'une attention toute particulière de la part des exploitants forestiers et des scientifiques depuis plusieurs décennies. Établir un bilan exhaustif actualisé des connaissances acquises sur leur taxonomie et leur écologie afin d'en dégager des pistes de nouvelles recherches est le but de cette synthèse bibliographique. Littérature. Le genre Entandrophragma compte des espèces (10 à 12) exclusivement africaines et qui sont exploitées pour la qualité de leur bois. Ces espèces sont répandues dans la région guinéo-congolaise (6 espèces) et dans les régions zambézienne et afromontagnarde (5 espèces). Le genre est caractérisé par une évolution taxonomique qui s'est traduite par une importante synonymie des noms d'espèces (36 à 37). Des études écologiques un peu larges ont été réalisées sur quelques principales espèces commerciales (Entandrophragma angolense, Entandrophragma congoense, Entandrophragma candollei, Entandrophragma cylindricum, Entandrophragma palustre et Entandrophragma utile) dans leurs zones phytogéographiques comprises principalement dans la région guinéo-congolaise. Conclusions. Les informations sur la taxonomie et l'écologie des espèces d'arbres d'Entandrophragma des forêts claires et des savanes sont insuffisantes comparativement à celles des forêts denses humides. Des travaux de recherches devraient être développés pour l'amélioration des connaissances taxonomiques, génétiques et la maitrise de leur écologie en vue de formuler des recommandations adéquates en matière de préservation et de gestion durable de ces espèces. (Résumé d'auteur

Consistent patterns of common species across tropical tree communities

Trees structure the Earth’s most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations1,2,3,4,5,6 in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth’s 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories7, we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world’s most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees.Publisher PDFPeer reviewe

Methodology for the treatment of increment cores to assess the vessel size distribution of a tree along a pith-to-bark transect

The sampling of increment cores constitutes a non-destructive approach to study the wood anatomy of a tree along a radial transect. The distribution and variability of anatomical features along such a transect can serve as a proxy of a tree’s growth dynamics. It is therefore valuable to develop methods of accessing and analyzing these data, such as the distribution of vessel sizes along a pith-to-bark transect. The processing of the increment cores begins with the production of long cross sections, 10 to 20 µm thick, using a microtome. The cross sections are then stained to highlight the anatomical features. Next, the cross sections are digitized using the Stream Motion software (Olympus Optical Co. Japan) on a scanning stage (SCAN 100 x 100, Märzhäuser Wetzlar, Germany) to create high resolution images. A pre-treatment of the images, with an image manipulation program such as GIMP 2 (www.gimp.org), is then required to enable their use for data analyses. This includes associating fragments to reconstruct a linear and continuous cross section, since it is difficult to consistently prevent the formation of tearing when cutting the cores. The data contained in the cross section images is finally accessed using the ImageJ software (www.imagej.net). Data such as the position, size, and vessels density along a pith-to-bark transect are then acquired and can therefore be used to study the physiology and growth dynamics of the trees. ImageJ features such as the Trainable Weka Segmentation plugin offer the opportunity to automatize the analyses, therefore allowing for a larger sampling size and faster processing

Entandrophragma : taxonomy and ecology of a genus of African tree species with economic importance : a review

Introduction: Entandrophragma tree species have been the subject of special attention by foresters and scientists for several decades. The purpose of this bibliographic review is to examine the current knowledge acquired on the taxonomy and ecology of this genus in order to identify new research priorities. Literature: The genus Entandrophragma has exclusively African species (10 to 12) that are exploited for the quality of their wood. These species are widespread in the Guineo-Congolese region (6 species) and in the Zambezian and Afromontane regions (5 species). The genus is characterized by a taxonomic evolution that has resulted in an important synonymy of species names (36 to 37). Ecological studies have been carried out on some major commercial species (Entandrophragma angolense, Entandrophragma congoense, Entandrophragma candollei, Entandrophragma cylindricum, Entandrophragma palustre and Entandrophragma utile) in their phytogeographic zones, mainly in the Guineo-Congolese region. Conclusions: Taxonomy and ecology of Entandrophragma tree species typically occurring in woodlands and savannas have been insufficiently studied in comparison with Entandrophragma species occurring in rainforests. Research needs to be developed for the improvement of taxonomic, genetic and ecological knowledge, with a view to formulating appropriate recommendations for the conservation and sustainable management of these species.Le genre Entandrophragma (Meliaceae) : taxonomie et écologie d’arbres africains d’intérêt économique (synthèse bibliographique) Introduction: Les espèces d’arbres du genre Entandrophragma font l’objet d’une attention toute particulière de la part des exploitants forestiers et des scientifiques depuis plusieurs décennies. Établir un bilan exhaustif actualisé des connaissances acquises sur leur taxonomie et leur écologie afin d’en dégager des pistes de nouvelles recherches est le but de cette synthèse bibliographique. Littérature: Le genre Entandrophragma compte des espèces (10 à 12) exclusivement africaines et qui sont exploitées pour la qualité de leur bois. Ces espèces sont répandues dans la région guinéo-congolaise (6 espèces) et dans les régions zambézienne et afromontagnarde (5 espèces). Le genre est caractérisé par une évolution taxonomique qui s’est traduite par une importante synonymie des noms d’espèces (36 à 37). Des études écologiques un peu larges ont été réalisées sur quelques principales espèces commerciales (Entandrophragma angolense, Entandrophragma congoense, Entandrophragma candollei, Entandrophragma cylindricum, Entandrophragma palustre et Entandrophragma utile) dans leurs zones phytogéographiques comprises principalement dans la région guinéo-congolaise. Conclusions: Les informations sur la taxonomie et l’écologie des espèces d’arbres d’Entandrophragma des forêts claires et des savanes sont insuffisantes comparativement à celles des forêts denses humides. Des travaux de recherches devraient être développés pour l’amélioration des connaissances taxonomiques, génétiques et la maitrise de leur écologie en vue de formuler des recommandations adéquates en matière de préservation et de gestion durable de ces espèces