Adaptation d’un cultivar de Niébé (Vigna unguiculata (L.) Walp.) aux conditions pédoclimatiques de Boundji (République du Congo)

L’étude réalisée sur un cultivar de niébé dans la zone de Boundji en République du Congo se justifie par la recherche des plantes fourragères à utiliser pour l’amélioration des pâturages. L’objectif de cette étude estd’avoir des données préliminaires sur la croissance et la production de ce cultivar de niébé en rapport avec les conditions pédoclimatiques de la zone. Le pouvoir germinatif des graines a été évalué, avant le semis etaprès la récolte. Le semis a été fait en ligne sur des buttes avec un espacement de 75 cm x 50 cm. Les résultats obtenus montrent que le niébé a un bon pouvoir germinatif (92 %), la croissance est normale, laproduction foliaire moyenne est bonne à deux mois après le semis (888 kg/ha) et celle de graines sèches récoltées à trois mois est faible (184 kg/ha). Ce cultivar s’adapte bien aux conditions écologiques de la zone.La production élevée de feuilles pourrait faire de ce cultivar une plante fourragère à prendre en compte dans des programmes d’aménagement des pâturages au Congo et ailleurs.Mots-clés : Niébé, croissance, production foliaire, production en graines, zone de Boundji

Allometric equation for Raphia laurentii De Wild, the commonest palm in the central Congo peatlands

The world's largest tropical peatland lies in the central Congo Basin. Raphia laurentii De Wild, the most abundant palm in these peatlands, forms dominant to mono-dominant stands across approximately 45% of the peatland area. R. laurentii is a trunkless palm with fronds up to 20 m long. Owing to its morphology, there is currently no allometric equation which can be applied to R. laurentii. Therefore it is currently excluded from aboveground biomass (AGB) estimates for the Congo Basin peatlands. Here we develop allometric equations for R. laurentii, by destructively sampling 90 individuals in a peat swamp forest, in the Republic of the Congo. Prior to destructive sampling, stem base diameter, petiole mean diameter, the sum of petiole diameters, total palm height, and number of palm fronds were measured. After destructive sampling, each individual was separated into stem, sheath, petiole, rachis, and leaflet categories, then dried and weighed. We found that palm fronds represented at least 77% of the total AGB in R. laurentii and that the sum of petiole diameters was the best single predictor variable of AGB. The best overall allometric equation, however, combined the sum of petiole diameters (SDp), total palm height (H), and tissue density (TD): AGB = Exp(-2.691 + 1.425 × ln(SDp) + 0.695 × ln(H) + 0.395 × ln(TD)). We applied one of our allometric equations to data from two nearby 1-hectare forest plots, one dominated by R. laurentii, where R. laurentii accounted for 41% of the total forest AGB (with hardwood tree AGB estimated using the Chave et al. 2014 allometric equation), and one dominated by hardwood species, where R. laurentii accounted for 8% of total AGB. Across the entire region we estimate that R. laurentii stores around 2 million tonnes of carbon aboveground. The inclusion of R. laurentii in AGB estimates, will drastically improve overall AGB, and therefore carbon stock estimates for the Congo Basin peatlands

Pantropical variability in tree crown allometry

Aim: Tree crowns determine light interception, carbon and water exchange. Thus, understanding the factors causing tree crown allometry to vary at the tree and stand level matters greatly for the development of future vegetation modelling and for the calibration of remote sensing products. Nevertheless, we know little about large‐scale variation and determinants in tropical tree crown allometry. In this study, we explored the continental variation in scaling exponents of site‐specific crown allometry and assessed their relationships with environmental and stand‐level variables in the tropics. / Location: Global tropics. / Time period: Early 21st century. / Major taxa studied: Woody plants. / Methods: Using a dataset of 87,737 trees distributed among 245 forest and savanna sites across the tropics, we fitted site‐specific allometric relationships between crown dimensions (crown depth, diameter and volume) and stem diameter using power‐law models. Stand‐level and environmental drivers of crown allometric relationships were assessed at pantropical and continental scales. / Results: The scaling exponents of allometric relationships between stem diameter and crown dimensions were higher in savannas than in forests. We identified that continental crown models were better than pantropical crown models and that continental differences in crown allometric relationships were driven by both stand‐level (wood density) and environmental (precipitation, cation exchange capacity and soil texture) variables for both tropical biomes. For a given diameter, forest trees from Asia and savanna trees from Australia had smaller crown dimensions than trees in Africa and America, with crown volumes for some Asian forest trees being smaller than those of trees in African forests. / Main conclusions: Our results provide new insight into geographical variability, with large continental differences in tropical tree crown allometry that were driven by stand‐level and environmental variables. They have implications for the assessment of ecosystem function and for the monitoring of woody biomass by remote sensing techniques in the global tropics

Tallo: A global tree allometry and crown architecture database.

This is the final version. Available from Wiley via the DOI in this record. Data capturing multiple axes of tree size and shape, such as a tree's stem diameter, height and crown size, underpin a wide range of ecological research-from developing and testing theory on forest structure and dynamics, to estimating forest carbon stocks and their uncertainties, and integrating remote sensing imagery into forest monitoring programmes. However, these data can be surprisingly hard to come by, particularly for certain regions of the world and for specific taxonomic groups, posing a real barrier to progress in these fields. To overcome this challenge, we developed the Tallo database, a collection of 498,838 georeferenced and taxonomically standardized records of individual trees for which stem diameter, height and/or crown radius have been measured. These data were collected at 61,856 globally distributed sites, spanning all major forested and non-forested biomes. The majority of trees in the database are identified to species (88%), and collectively Tallo includes data for 5163 species distributed across 1453 genera and 187 plant families. The database is publicly archived under a CC-BY 4.0 licence and can be access from: https://doi.org/10.5281/zenodo.6637599. To demonstrate its value, here we present three case studies that highlight how the Tallo database can be used to address a range of theoretical and applied questions in ecology-from testing the predictions of metabolic scaling theory, to exploring the limits of tree allometric plasticity along environmental gradients and modelling global variation in maximum attainable tree height. In doing so, we provide a key resource for field ecologists, remote sensing researchers and the modelling community working together to better understand the role that trees play in regulating the terrestrial carbon cycle.Natural Environment Research Council (NERC)Natural Environment Research Council (NERC); Ministry of Education, Youth and Sports of the Czech RepublicFAPEMIGUniversidad Nacional Autónoma de MéxicoUniversidad Nacional Autónoma de MéxicoConsejo Nacional de Ciencia y TecnologíaSwedish Energy AgencyUKRIFederal Ministry of Education and ResearchNational Natural Science Foundation of ChinaNational Natural Science Foundation of ChinaNational Science FoundationNational Science FoundationInternational Foundation for ScienceP3FACDynAfForNanjing Forestry UniversityJiangsu Science and Technology Special ProjectHebei UniversityAgence Nationale de la RechercheAgence Nationale de la RechercheAgua Salud ProjectU.S. Department of EnergyCAPE

Effets de l'élimination de la végétation concurrente sur l'humidité du sol et sur la croissance initiale d'une plantation monoclonale d'Eucalyptus 12ABLxsaligna

Effects of the Herbaceous Vegetation Removing on the Soil Moisture and on the Initial Growth of a Monoclonal Plantation of Eucalyptus 12 ABL x Saligna. A trial has been carried out in congolese coastal savanna in order to determine the distance to which herbaceous vegetation should be removed around young Eucalyptus 12 ABL x saligna. Eucalyptus were planted within weeded circles of variable radius : 0, 35, 70, 105, 140 and 175 cm. Eight months afterplanting, the herbaceous vegetation did not have a negative sensible effect on the revival of the Eucalyptus. Twenty seven months after planting the rate of survival was still high. It accounted for about 59 % and superior to 78 % in the proof and other treatments respectively. The observations made on the vigor and the growth has shown that plants within circles of 0 and 35 cm radius were competed with spontaneous vegetation. Weedings within circles of 70 and 105 cm of radius were sufficient to preserve enough soil moisture and therefore to ensure the survival and to increase in very important proportions the growth of young Eucalyptus. A radius higher 105 cm has shown any significant advantage. It has been found that plantation watering mainly during dry season was capital to help plant juvenile growth

Évaluation du profil minéral des èspeces fourragères et de la capacité de charge des savanes de la Cuvette congolaise (République Du Congo)

Les potentialités fourragères ont été évaluées dans la Cuvette congolaise, à partir des teneurs en éléments minéraux des fourrages et de la capacité de charge des savanes au Nord du Congo (Ollombo, Boundji, Owando, Makoua). Les échantillons de fourrages ont été récoltés dans des parcelles retenues dans chaque type de savanes puis analysés pour leur  composition minérale. La capacité de charge de chaque savane a été évaluée à partir de la phytomasse maximale. Les résultats obtenus  montrent que les espèces fourragères de la Cuvette congolaise sont dansl’ensemble riches en Mg (1,42-4,28 g/kg, pour Hyparrhenia diplandra et 1,51-2,37 g/kg, pour Loudetia simplex), K (5,67-11,6 g/kg, pour H. diplandra et 6,00-9,85 g/kg, pour L. simplex), Mn (83,3-121 mg/kg, pour H. diplandra et 61,2-131 mg/kg, pour L. simplex) et Fe (160-657 mg/kg, pour H. diplandra et 103 mg/kg pour L. simplex), car les valeurs trouvées sont au dessus des normes. Ces teneurs peuvent satisfaire les besoins de croissance et de reproduction des bovins et non ceux de production de lait. Une complémentation minérale est donc nécessaire dans la gestion de l’élevage dans cette zone. La charge de 1,21 ± 0,52 ha/UBT/an est la charge théorique moyenne que peuvent supporter les savanes étudiées.Mots clés : Savanes, fourrages, éléments minéraux, capacités de charge, Cuvette congolaise.EVALUATION OF MINERAL PROFILE OF FORAGE AND CARRYING CAPACITY OF SAVANNAHS CONGOLESE BASIN (REPUBLIC OF CONGO)The forage potentialities have been evaluated in Congolese Basin using mineral profile of forages and carrying capacity of savannahs in Ollombo, Boundji, Owando and Makoua from the northern of Congo. The forage samples were collected from selected plots in each type savannah and analyzed for their mineral composition. The carrying capacity of each savannah has been evaluated from the maximal phytomass. Result showing that the forages of the Congolese Basin are rich in magnesium(1.42 to 4.28 g / kg, for Hyparrhenia diplandra and 1.51 to 2.37 g / kg, for Loudetia simplex), potassium (5.67 to 11.6 g / kg, for H. Diplandra and 6.00 to 9.85 g / kg, for L. simplex), manganese (83.3 to 121 mg / kg for H . diplandra and 61.2 to 131 mg / kg for L. simplex) and iron (160-657 mg /kg for H. diplandra and 103 mg / kg for L. simplex), because the values are found above the norms. These levels can meet the needs of growth and reproduction of cattle and not those of milk production. A mineral supplement is therefore relevant for the management of breeding in this area. The carrying capacity of 1.21 ± 0.52 ha / TLU / year is the theoretical average than savannas can withstand studied.Keywords : Savannahs, forages, mineral contents, carrying capacity, Congolese Basin

Analyse De La Diversite Floristique Du Sous-Bois De La Palmeraie De Mbobo Dans La Cuvette Congolaise (Republique Du Congo)

Dans la Cuvette congolaise, les palmeraies sont implantées dans des zones forestières pour des besoins d’huile de palme. Cependant, leur sous-bois connait une exploitation limitée comme pâturage et sa diversité floristique n’est pas assez connue. C’est ainsi que la présente étude a été réalisée avec pour objectif général d’évaluer l’intérêt pastoral du sous-bois de la palmeraie de Mbobo. Spécifiquement il s'agit de : (1) inventorier la diversité floristique ; (2) identifier les espèces fourragères. L’inventaire floristique a été réalisé par la méthode de transects et la diversité floristique évaluée à partir des indices de diversité de Shannon-Weaver et d’équitabilité de Pielou. Les résultats obtenus montrent que le sous-bois de la palmeraie de Mbobo présente 93 espèces réparties en 76 genres et 39 familles, sur une superficie de 900m2 représentant l'ensemble des trois parcelles prospectées. Les espèces fourragères représentent 25 % de l'ensembles des espèces recensées. Elles sont dominées par les Poaceae et les Cyperaceae. Les indices de diversité (4,8-5) et de régularité (0,6-0,9) sont très élevés. Le sous-bois de la palmeraie présente donc une richesse floristique élevée et une qualité fourragère importante qui permettrait de l’exploiter comme pâturage.Mots clés : Cuvette congolaise, palmeraie, sous-bois, diversité floristique, pâturageIn the Congolese Basin, the palm groves are located in forest areas for oil palm production. However, their undergrowth knows as limited for grazing and their floristic diversity is not well known. Thus, the present study whose main objective was to assess the pastoral value of undergrowth of palm grove of Mbobo was conducted. The specific objectives were to: (1) inventory the floristic diversity, (2) identify the forage species. The floristic inventory was performed by the transect method and plant diversity was estimated by the Shannon-Weaver index and Pielou evenness index. The forage species were identified by the food tracking sheep in the palm grove. The undergrowth vegetation of the palm grove of Mbobo is composed of 93 species in 76 genus and 39 families. The most representative families in number of species are Poaceae (10 %), Fabaceae (7 %), Rubiaceae (7 %), Verbenacea (7 %), Cyperaceae (5 %) and Malvaceae (5 %). Forage species represent 25 % and are dominated by Poaceae and Cyperacea. Diversity (0.6 - 0.9) and evenness (4.8 - 5) indices are very high. The undergrowth of this palm grove exhibits a high floristic diversity and important forage quality, and it could therefore be exploited as pasture. Forages spcies could be introduced under the palm grove to encourage the development of agropastoralism.Key words : Congolese Basin, palm grove, undergrowth, plant diversity, grazingArticle in Frenc

Biomasse et stocks de carbone des forêts tropicales africaines (synthèse bibliographique)

Biomass and carbon stocks of tropical African forests. A review. Introduction. Quantifying the biomass and carbon stocks contained in tropical forests has become an international priority for the implementation of the REDD+ mechanism. Forest biomass is estimated at three successive levels: the tree, the stand and the region level. This paper reviews the state of the art regarding the estimation of biomass and carbon stocks in tropical African forests. Literature. This review highlights the fact that very few allometric equations, equations used for estimating the biomass of the tree using non-destructive measurements (diameter, height), have been established for tropical African forests. At the stand level, the review highlights the spatial and temporal variations in biomass between forest types in Central and Eastern Africa. While biomass recovery after a disturbance (logging, for instance) is rather quick, a great deal of uncertainty still remains regarding the spatial variation in biomass, and there is no consensus on a regional biomass map. The quality of biomass mapping in tropical Africa strongly depends on the type of remotely-sensed data being used (optical, RADAR or LIDAR), and the allometric equation used to convert forest inventory data into biomass. Conclusions. Based on the lack of precision of the available allometric equations and forest inventory data and the large spatial scale involved, many uncertainties persist in relation to the estimation of the biomass and carbon stocks contained in African tropical forests

Plantation forests and biodiversity: oxymoron or opportunity?

Losses of natural and semi-natural forests, mostly to agriculture, are a significant concern for biodiversity. Against this trend, the area of intensively managed plantation forests increases, and there is much debate about the implications for biodiversity. We provide a comprehensive review of the function of plantation forests as habitat compared with other land cover, examine the effects on biodiversity at the landscape scale, and synthesise context-specific effects of plantation forestry on biodiversity. Natural forests are usually more suitable as habitat for a wider range of native forest species than plantation forests but there is abundant evidence that plantation forests can provide valuable habitat, even for some threatened and endangered species, and may contribute to the conservation of biodiversity by various mechanisms. In landscapes where forest is the natural land cover, plantation forests may represent a low-contrast matrix, and afforestation of agricultural land can assist conservation by providing complementary forest habitat, buffering edge effects, and increasing connectivity. In contrast, conversion of natural forests and afforestation of natural non-forest land is detrimental. However, regional deforestation pressure for agricultural development may render plantation forestry a 'lesser evil' if forest managers protect indigenous vegetation remnants. We provide numerous context-specific examples and case studies to assist impact assessments of plantation forestry, and we offer a range of management recommendations. This paper also serves as an introduction and background paper to this special issue on the effects of plantation forests on biodiversity