Woody flora and dynamic of Aucoumea klaineana forest in the Congolese littoral

The floristic dynamics of the woody facies of the Aucoumea klaineana forest of the Congolese littoral has been done according to a gradient evolving of the pioneer front towards the interior of the ecosystem. This settlement integrates a dynamics going from the youthful stages towards the most stable of this formation. The objective of this study was focused on the dynamics of the woody formation, the monodominant installation of the Aucoumea klaineana facies with d1.30 . 10 cm and highlights the evolution and the correlation between the density, the basal area and the floristic diversity. The phytoecological parameters count 1186 trees of d1.30 . 10 cm (an average 395 arbres.ha-1) for 71 species. The trees number by subplot oscillated between 70 and 159 trees (6 to 13% of listed trees). The species number by subplot varies from 8 to 28 (11 to 39% of inventoried species). Basal area by plot oscillates of 22 and 35 m2.ha-1 (27 m2.ha-1 an average). It varies from 4 to 10 m2 per subplot (7 m2 by . ha an average). The trees number by subplot and diameter classes vary from 3 to 636 trees (1 to 212 trees.ha-1 an average). The trees of 10 < d1.30 . 20 cm are dominating with 54% and this prevalence is regular in all the subplots. As for the indices of diversity, the Green index (GI) decrease from 0.9 to 0.1 as the ecosystem increases in age. This observation is also true for the skewness coefficient which regresses from pioneer front towards the interior of the forest. The values are respectively 2.10-2 in the first plot, 7.10-4 in the second and 4.10-3 for the third. In this inventory where Aucoumea klaineana is dominating, its density by subplot varies from 42 to 384 trees.ha-1 (183 trees.ha-1 an average). Just like the density, basal area is decreasing to pioneer front towards the interior of the forest. The values oscillate from 87 to 32% of basal area of the subplot (19 m2.ha-1 an average). The report basal area by the density of Aucoumea klaineana is lower than 1 for an average of 0.1. The ecological parameters analysis which allowed seizing the floral dynamics of this forest is stressed by a numerical multivariate analysis (grouping and ordination). It highlights the weak resemblance degree between the twelve plots of the inventory and clearly marks the existence of variation characterizing the Congolese coastal forest, notably during the first stages of installation.Keywords: Congo, Aucoumea klaineana, biological diversity indices, Coastal forest, floristic diversity, phytoecological parameters

Productivité herbacée des savanes de la Cuvette congolaise (Congo-Brazzaville)

La savane à Hyparrhenia diplandra Stapfet celle à Loudetia simplex C.E. Hubbard ont été étudiées dans la Cuvette congolaise (Nord du Congo-Brazzaville), sur le plan de la production herbacée. Les sites retenus pour l’étude sont Ollombo, Owando et Makoua. L’étude a démarré à partir des feux de la saison « sèche ». L’objectif de cette étude était d’évaluer la phytomasse aérienne herbacée et sa productivité, en vue d’aider à la prise de décision sur le choix des espaces à occuper pour des activités agricoles et pastorales. Laphytomasse aérienne herbacée a été mesurée par la méthode de la récolte et sa productivité primaire nette réelle par la méthode de la différence entre le moment où la phytomasse est maximale et le moment où elle est minimale dans un cycle annuel. Les échantillons de sols ont été prélevés sous ces deux types de savanes. Leurs analyses granulométrique et chimiques révèlent que ces sols sont dans l’ensemble très sableux, acides et pauvres en matière organique. Le taux en argiles est légèrement supérieur dans le sol sous savane à H. diplandra (jusqu’à 14%) que dans celui sous savane à L. simplex (1% au maximum). La phytomasse aérienne totale maximale est enregistré à dix mois après les feux, en mai : 9,48 – 10,44 t MS ha-1 pour la savane à H. diplandra et 3,43 – 4,52 t MS ha-1 pour la savane à L. simplex. La productivité de la phytomasse varie de 9,29 – 10,04 t MS ha-1an-1 pour la savane à H. diplandra et de 3,09 – 4,64 t MS ha-1an-1 pour la savane à L. simplex. La savane à H. diplandra serait donc à recommander pour des activitésagricoles et pastorales que celle à L. simplex.Mots-clés : savanes, sols, phytomasse, strate aérienne herbacée, productivité, cuvette congolaise.Productivity of Congolese Basin savannas (Congo-Brazzaville)The Hyparrhenia diplandra Stapf and the Loudetia simplex C.E. Hubbard savannas have been studied in the Cuvette congolaise (the North of Congo-Brazzaville) on the herbaceous production level. The selected sites for this research are: Ollombo, Owando and Makoua. The study started with the fires of the dry season. The objective of this survey was to evaluate the aerial herbaceous phytomass and its productivity, in order to help the decision taking concerning the choice of the areas for agricultural and pastoral activities. Theherbaceous aerial phytomass has been examined within the harvesting framework and the net primary productivity of the phytomass is determined by the method of difference between the time when the phytomass is maximal and when it is minimal in an annual cycle. The soil samples have been taken from these two types of savannas. The granulometric and chemical analyses of soils reveal that the soils of the studied savannas are generally very sandy (79, 94-98, 38 %), acidic and poor in organic materials. The clay rate is slightly superior in the soil of the H. diplandra savanna (up to 14%) than in that of L. simplex (1% maxi). The maximal total aerial phytomass is recorded ten months after the fires, in may: 9, 48-10, 44 t MS ha-1 for H. diplandra savanna and 3, 43-4, 52 t MS ha-1 for L. simplex savanna (Figures 1 and 2). The phytomass productivity varies from 9, 29-10, 04 t MS ha-1an-1 for H. diplandra and from 3, 09-4, 64 t MS ha-1 an-1 for L. simplex. The H. diplandra savanna is more productive than the L. simplex savanna. The former should be recommended for agricultural and pastoral activities than the latter.Keywords : savannas, soils, phytomass, herbaceous aerial stratum, productivity, congolese cuvette

Évaluation de la diversité floristique en herbacées des savanes de la cuvette congolaise (République du Congo)

Les savanes de la République du Congo sont exploitées pour des fins agricoles et pastorales. Dans la Cuvette congolaise (nord du Congo), les savanes sont encore peu étudiées. La gestion durable de ces savanes nécessite leur connaissance sur le plan floristique. C’est ainsi qu’une étude floristique a été menée dans les savanes de la zone. Elle avait pour objectif d’évaluer l’intérêt pastoral des savanes de cette cuvette. A cet effet, des relevés floristiques ont été réalisés par la méthode des points quadrats alignés, afin d’inventorier la diversité floristique et les principales espèces fourragères. Ainsi, 37 espèces réparties en 33 genres et 10 familles ont été recensées dans la savane à Hyparrhenia diplandra (Hack.) Stapf , et 27 espèces réparties en 22 genres et 8 familles dans la savane à Loudetia simplex (Nees) C.E. Hubbard. Dans l’ensemble, les familles les plus riches en espèces étaient les Poaceae, les Fabaceae et les Cyperaceae. L’indice de diversité de Shannon et l’équitabilité de Piélou avaient des valeurs moyennes de 2,23 bits et 0,57 pour la savane à H. diplandra, et entre 2,1bits et 0,61 pour la savane à L. simplex. Il y a donc une diversité floristique non négligeable, dans ces savanes. Elle varie en fonction des stations d’étude et des phytocénoses. Une gestion planifiée de ces formations permettrait d’assurer une meilleure planification pour des fins pastorales.Mots-clés : savanes, phytodiversité, herbacée, pastoralisme, cuvette congolaise.Evaluation of herbaceous floristic diversity of Congolese basin savannahs (Republic of Congo)The savannas of the Republic of Congo are exploited for agricultural and pastoral. In the Congolese Basin (northern Congo), savannas are still poorly studied. Sustainable management of these savannas requires knowledge in terms of flora. Thus, a floristic study was conducted in the savannah area. It aimed to assess the value of pastoral savannas of the basin. To this end, the floristic surveys were conducted by the method of quadrat points aligned to inventory plant diversity and major forage species. Thus, 37 species, 33 kinds and 10 families were identified in the savannah of Hyparrhenia diplandra (Hack.) Stapf and 27 species, 22 kinds and 8 families in the savannah of Loudetia simplex (Nees) CE Hubbard. Overall, the richest families in species were Poaceae, Fabaceae and the Cyperaceae. The Shannon diversity index and equitability of Pielou had average values of 2.23 bits and 0.57 for the savannah of H. diplandra, and between 2.1 bits and 0.61 for the savannah of L. simplex. So there is substantial plant diversity in these savannas. It varies from study sites and phytocenoses. Planned management of such training would ensure better planning for pastoral purposes.Keywords : savannas, plant diversity, herbaceous, pastoralism, congolese basin

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

Analysis of the Effect of Scarification Process on Papaya (<em>Carica papaya</em> Lin.) Seeds Germination

The presence of the aril (sarcotesta) in the papaya causes a slow and low germination, being necessary to break the state of dormancy. Calcium hydroxide that was applied in order to evaluate its scarifying effect was the objective. The sample consisted of 60 randomly selected fruits of hermaphrodite plants in a commercial production batch of approximately 1 ha (2222 plants) showing commercial maturity, of homogeneous size (±2 kg). The treatments were calcium hydroxide Ca(OH)2 at three doses, dipping the seed for a period of 24 h; the standardized sodium hydroxide (NaOH) at 25% with a 15 min immersion time. The highest germination and vigor seeds were obtained applied Ca(OH)2 with highly significant differences respect to the rest treatment, especially for the dose of 60 g l−1 of water for reasons of diminishing expenses. Significant correlations were found, with direct relations (aril and mechanical damage) and inverse relations (abnormal seeds) between the variables evaluated related to the vigor and germination of the seeds. It can be an ecological and not expensive methodology to improve the germination and vigor of papaya seeds in relation to other chemical compounds to scarify

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

Leveraging Signatures of Plant Functional Strategies in Wood Density Profiles of African Trees to Correct Mass Estimations From Terrestrial Laser Data

peer reviewedWood density (WD) relates to important tree functions such as stem mechanics and resistance against pathogens. This functional trait can exhibit high intraindividual variability both radially and vertically. With the rise of LiDAR-based methodologies allowing nondestructive tree volume estimations, failing to account for WD variations related to tree function and biomass investment strategies may lead to large systematic bias in AGB estimations. Here, we use a unique destructive dataset from 822 trees belonging to 51 phylogenetically dispersed tree species harvested across forest types in Central Africa to determine vertical gradients in WD from the stump to the branch tips, how these gradients relate to regeneration guilds and their implications for AGB estimations. We find that decreasing WD from the tree base to the branch tips is characteristic of shade-tolerant species, while light-demanding and pioneer species exhibit stationary or increasing vertical trends. Across all species, the WD range is narrower in tree crowns than at the tree base, reflecting more similar physiological and mechanical constraints in the canopy. Vertical gradients in WD induce significant bias (10%) in AGB estimates when using database-derived species-average WD data. However, the correlation between the vertical gradients and basal WD allows the derivation of general correction models. With the ongoing development of remote sensing products providing 3D information for entire trees and forest stands, our findings indicate promising ways to improve greenhouse gas accounting in tropical countries and advance our understanding of adaptive strategies allowing trees to grow and survive in dense rainforests. © 2020, The Author(s)

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

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

Changes in eucalypt litter quality during the first three months of field decomposition in a Congolese plantation

In fast-growing tree plantations, decomposition of leaf litter is considered as a key process of soil fertility. A three-month field experiment, spanning both rainy and dry seasons, was conducted to determine how changes in litter decomposition affect the main parameters of litter quality-namely, the concentrations of phenolic and non-phenolic carbon (C) compounds, nitrogen (N), and fibres, and the litter C mineralization rate. This Study was conducted to test (1) if these changes vary according to the Compound and to the season, and if they are greater for soluble compounds, and (2) if after a three-month period of field decomposition, the chemical composition of the remaining litter drives C mineralization, as measured in laboratory conditions, through a greater influence on the concentration of N and lignin. We found that the concentrations of water- and methanol-soluble phenolic compounds and the concentrations of non-phenolic compounds decreased during decomposition in all plots and in each season, while the fibre and N concentrations increased. The relationships among litter decomposition, C mineralization, and litter quality depended on the season, which strongly suggests that different processes are involved in dry and rainy seasons. The C mineralization rates were driven by soluble organic Compounds in the initial litter and by soluble phenolic compounds in the decomposed litter