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Structure spatiale et régénération naturelle de Pterocarpus erinaceus Poir en zone soudanienne au Bénin

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... Ce type d'inventaire consiste à délimiter des unités primaires ou placettes à l'intérieur desquelles les mesures sont effectuées. Dans chaque massif, la collecte des données a été faite à l'intérieur de 10 placettes de 50 m x 50 m avec une équidistante de 50 m suivant la méthode décrite par plusieurs auteurs(Kelly, 2006 ;Glèlè Kakaï et al., 2009). Les mesures ont été portées sur des individus de diamètre supérieur à 3 cm de toutes espèces confondues et particulièrement celles utilisées dans l'alimentation humaine. ...
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Résumé Le présent travail a été initié dans le but d'évaluer la composition floristique, la diversité spécifique et la structure des espèces forestières locales alimentaires en vue de lutter contre la malnutrition. Il a été réalisé dans des villages de quatre massifs forestiers naturels appartenant à deux zones agro-écologiques au Sud du Mali, soit deux villages par zone. Au niveau de chaque massif forestier, les données ont été collectées dans 10 placettes de 50 m x 50 m suivant un échantillonnage systématique à un degré. Dans chaque placette, tous les individus ligneux ont été mesurés. Les données dendrométriques ont été collectées sur chaque arbre (diamètre à hauteur de poitrine appelée en anglais « diameter at breast height » en abrégé « d.b.h. » et la hauteur totale des tiges). Au niveau de chaque placette, le comptage de l'effectif total des jeunes plants (diamètre à hauteur de poitrine < 3 cm) a été effectué dans cinq placeaux de 25 m² suivant un échantillonnage systématique à deux degrés. Les relevés effectués ont permis de recenser 89 espèces ligneuses appartenant à 73 genres et 30 familles botaniques. Les espèces alimentaires représentent 34,83 % des espèces inventoriées. Des différences significatives de densité, de hauteur totale et de surface terrière moyenne ont été observées entre les massifs forestiers. La densité la plus élevée est observée au niveau du massif forestier de Badogo (71 arbres/ha) et la plus faible au niveau de Sorobasso (24 arbres/ha) qui présente le plus fort taux de régénération (2,88 %). L'analyse des structures en classe de diamètre des populations d'espèces alimentaires les plus abondantes (157 et de multiplication végétative des espèces s'avèrent nécessaires pour assurer la disponibilité de la ressource en vue de lutter contre la malnutrition. Abstract The present work was launched to assess the floristic composition and structure of the native forest food species in order to tackle malnutrition. It was carried out in four natural forest from villages in two agro-ecological zones (two villages per agro-ecological zone) in southern Mali. In each natural forest, data were collected in 10 plots of 50 x 50 m using sampling systematic to one degree. In each plot, all tree were measured. Dendrometric data were collected on each tree (diameter at breast height or d.b.h and total stem height). In each plot, the total number of seedlings (diameter at breast height < 3 cm) was carried out within five 25 m² plots using sampling systematic to two degrees. The inventories were recorded 89 native forest species belonging to 73 genera and 30 botanical families. Native edible species were represented 34.83% of the overall inventoried species. Significant differences were observed between natural forest for average density per hectare, average height and average basal area. The high density was observed in Badogo (71 trees.ha-1), while the less in Sorobasso (24 trees.ha-1) which present the high regeneration rate (2.88%). The analysis of population diameter structures for Saba senegalensis, Vitellaria paradoxa, Lannea acida, Lannea microcarpa, Lophira lanceolata, Parkia biglobosa and Borassus aethiopum showed variable trends. Domestication and vegetative propagation strategies of the species are needed to ensure the availability of the resource to combat malnutrition.
... Other researchers identified also K. senegalensis, A. africana and P. erinaceus as threatened species (Adomou, 2005;Brisso et al., 2007;Teka et al, 2007;Houéhanou et al., 2008). Glèlè Kakaï et al. (2009) reported that P. erinaceus is used by local people for animal feeding, traditional medicine and timber). All this justify why particular attention must be payed for the rational uses of these species. ...
Thesis
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Native plant species in general and fodder trees in particular contribute significantly to the daily needs of both human and animal especially in developing countries. During the dry season, fodder trees are an important source for the survival of ruminants because of herbaceous forage lack. They are multipurpose species exploited by various actors who are sometimes protagonists. In view of the pressure faced by these trees, and their consequent rarity noted in rangelands, a study was conducted in the Guineo-Congolese/Sudanian transition zone of Benin at the level of the local population surrounding the protected forests of Monts Kouffé, Wari-Maro and Ouémé Supérieur. This thesis contributes to the rational management of fodder trees’ resources. Specifically, it aims at (i) evaluate the diversity, the pastoral and conservation priority of fodder trees; (ii) assess the influence of age, sex and ethnicity on the perception of fodder species use values; (iii) describe the relationship between the availability and the use status of fodder species; (iv) develop models for estimating leaf biomass of three priority browse species; (v) contribute to the understanding of the socio-cultural dynamics of the study area in relation to the fodder trees’ exploitation and the associated conflicts. A total of 220 informants belonging to three sociolinguistic groups (Bariba, Nago and Peul) were interviewed through a semi-structured survey on the fodder trees that they use for different purposes. The citation rates of the fodder trees by the surveyed populations were used to establish pastoral priority, while their conservation priority was established using a combination of four methods and nine criteria. The use categories were defined in the study area and at an international level for the use rates calculation. The ethnoecological approaches were used to analyze the availability of fodder tree species in the study region. A total of 25 trees per species were sampled for biomass estimating. Carrying capacity was determined for the dry season in the study area. A total of 48 fodder trees belonging to 17 families dominated by Leguminosae (27.1%) and Moraceae (16.6%) were reported. These species were distributed among 37 genera, with the genus Ficus being the most represented (16.6%). Palatability, species availability and the impact of tree fodder on animal productivity were the criteria used by the surveyed sociolinguistic groups in their selection of fodder trees. The prioritization methods yielded ten top ranked species: Afzelia africana, Pterocarpus erinaceus, Khaya senegalensis, Vitellaria paradoxa, Mangifera indica, Ficus platyphylla, Balanites aegyptiaca, Annona senegalensis, Ficus umbellata and Daniellia oliveri. As a multipurpose species, the fodder trees are classified in six use categories: food, medicine, construction, fuel, veterinary and fodder. A. africana, K. senegalensis and P. erinaceus are the most widely used species by Peul and Bariba sociolingustic groups to feed animals, while the Nagos use M. indica comes first followed by F. umbellata, F. platyphylla and P. Erinaceus. Combining the different use categories, overharvested or underutilized species depend significantly on the sociolinguistic group. The forest inventory revealed 63 tree species of dbh ≥ 10 cm distributed in 24 families and 52 genera. The most represented families in genus and species are Leguminosae (28.57 %), Combretaceae (14.28 %). The Leguminosae family had the highest importance values (FIVI=83.42) followed at a distance by Combretaceae (21.68). The most important and ecologically dominant species are V paradoxa (SIVI = 42.76); I. doka (41,88); B. ferruginea (22.98); and D. oliveri (16,18). It is also noted that aerial fodder production significantly varied among species. The best models that estimated leaf biomass production of A. africana and P. erinaceus were obtained with diameter at breast height; a plant trait not directly affected by pruning as predictors. For D. oliveri the best model uses the crown height as estimator parameter. Globally, the carrying capacity of each species is about 0.05 to 0.09 TLU ha-1an-1 for A. africana; 0.03 to 0.08 TLU ha-1an-1 for P. erinaceus and 0.04 to 0.79 TLU ha-1an-1 for D. oliveri. The number of animal that can sustainably be fed in the study area was 38 497 TLU. Conflicts arise between sawyers and foresters, between foresters and Peul (herders), farmers and herders, farmers and sawyers, foresters and farmers. These conflicts are caused by the illegal exploitation of trees for their timber and fodder, and the breeders camp near the agricultural areas or sometimes in the forest reserves. Direct negotiations between those involved in conflicts or the arbitration of a local authority were the main strategies and ways of these conflicts managing. With the aim of establishing a sustainable management of pasture lands, we suggest that priority be given to the pastoral and conservation priority species witch are also overexploited species in the restoration, afforestation/reforestation and plantation activities. The introduction of these fodder tree species in afforestation/reforestation activities can improve the availability of leaf biomass to feed animals. Keywords: Availability, Benin, Biodiversity, Conservation priority, Ethnoecology, Fodder trees, Leaf biomass, Pastoralism.
... Also, illegal settlements and agricultural encroachment on the protected forests [13] and expansion of illegal timber trade are considered as additional threats to the loss of forest resources. Yet, the most serious cause of the extinction of many woody species in the wild in Benin is undoubtedly the selective logging to which they may be subjected [2,7,14]. Atakora mountain chain is a region of great ecological and species diversity in the country [15]. ...
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Background Atakora mountains in Benin are a unique but fragile ecosystem, harboring many endemic plant species. The ecosystem is undergoing degradation, and the woody vegetation is dramatically declining due to high anthropogenic actions and recurrent drought. This study aimed to (i) assess the diversity of threatened woody species and (ii) identify their potential substitutes in the three regions of the Atakora mountains namely East Atakora, Central Atakora, and West Atakora. Methods The data were collected during expeditions on surveyed localities through semi-structured individual interviews. Free-listing was used to record threatened woody species and which were important and why. Alpha-diversity indices were used to assess diversity of threatened and important threatened woody species. A correspondence analysis was used to determine the reason supporting their importance. Differences in species composition were assessed using analysis of similarities. A number of potential substitutes were compared among species using generalized linear models. Results A total of 117 woody species (37 families and 92 genera) were identified. The most prominent families were Fabaceae (19.66%), Combretaceae (12.82%), and Moraceae (10.26%), and the richest genera were Ficus (10 species), Combretum (6), and Terminalia (5). Most threatened species differed across regions (East Atakora, Central Atakora, and West Atakora) and included Afzelia africana, Anogeissus leiocarpa, Borassus aethiopum, Diospyros mespiliformis, Khaya senegalensis, Milicia excelsa, and Pterocarpus erinaceus. Most socioeconomically important species (K. senegalensis, Parkia biglobosa, Vitellaria paradoxa, and V. doniana) were used mainly for food, timber, and fuelwood purposes. Old and adult people, and Dendi and Fulfulde sociolinguistic groups had greater knowledge of threatened woody plant species. High intercultural differentiations in species composition were detected between Bariba-Berba and Bariba-Natimba. Knowledge of substitutes also differed across regions with P. erinaceus, Isoberlinia spp., and A. africana being the most cited substitutes. Conclusion Basic data was provided here to inform decision and guide efficient management of woody resources. There was evidence that immediate conservation measures are required for some high economic value woody taxa which were critically threatened. Ex-situ conservation of these species while promoting their integration into agroforestry-based systems were recommended. Besides, community-based management programs and community led initiatives involving knowledgeable people from different horizons will lead to a long-lasting conservation of these threatened resources. Keywords: Beta-diversity, Atakora mountain chain, Socio-cultural factors, Forest resources, ANOSIM
... La connaissance de ces facteurs biotiques permet d'orienter la sylviculture dans le cadre de la gestion des peuplements de cette espèce. Plusieurs auteurs (Assogbadjo, 2006 ;Glèlè et al., 2009 ;Gouwakinnou et al., 2011) ont eu recours aux indices de Blackman et Green pour caractériser la structure des espèces étudiées. Ces indices renseignent certes la structure spatiale globale (grégaire ou aléatoire) d'un peuplement. ...
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The main purpose of this study was to analyse the population structure and spatial distribution of Sclerocarya birrea stands in the protected forests of Dan Kada Dodo and Dan Gado and their peripheral areas. These parameters have to be known to ensure that the stands are managed sustainably. Sample inventory plots measuring 50 x 20 m were identified by random stratified sampling in the three land use units identified (tree steppe, agroforestry sector, adjacent agricultural zones). Tree diameter at 1.30 m above the ground, total height and the two diameters perpendicular to the crown of S. birrea were measured. To define spatial distribution, S. birrea individuals were mapped in two 1.96 ha plots (140 x 140 m) in the "tree steppe" and "agroforestry sector" units. The results show that S. birrea individuals are distributed in random aggregates of varying sizes (about 7 m and 25 m), which is consistent with their zoochorous and barochorous fruit dispersal pattern and the capacity of the species for vegetative propagation. The highest densities (25.2 individuals/ha), basal areas (1.6 m2/ha) and average heights (6.9 m) were in the protected forest sectors. The bell-shaped distribution curve for stand height and diameter classes reflects the better representation of intermediate classes than extremes. However, the erratic structure observed in the "adjacent agricultural zones" indicates a highly irregular distribution of diameter classes. We conclude that S. birrea populations require more effective conservation, with more appropriate restoration strategies to be developed.
... La connaissance de ces facteurs biotiques permet d'orienter la sylviculture dans le cadre de la gestion des peuplements de cette espèce. Plusieurs auteurs (Assogbadjo, 2006 ;Glèlè et al., 2009 ;Gouwakinnou et al., 2011) ont eu recours aux indices de Blackman et Green pour caractériser la structure des espèces étudiées. Ces indices renseignent certes la structure spatiale globale (grégaire ou aléatoire) d'un peuplement. ...
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RÉSUMÉ STRUCTURE DÉMOGRAPHIQUE ET RÉPARTITION SPATIALE DES POPULATIONS DE SCLEROCARYA BIRREA (A. RICH.) HOCHST. DU SECTEUR SAHÉLIEN DU NIGER Cette étude a pour objectif principal d’analyser la structure démographique et la distribution spatiale des populations de Sclerocarya birrea dans les forêts classées de Dan Kada Dodo et de Dan Gado, et dans leurs zones périphériques. La connaissance de ces paramètres constitue une étape indispensable à leur gestion durable. Un échantillonnage stratifié aléatoire sur la base des trois unités d’occupation du sol identifiées (steppe arborée, parc agroforestier, zones agricoles riveraines) a permis la mise en place de placettes d’inventaire de 50 x 20 m. Le diamètre à 1,30 m du sol, la hauteur totale et les deux diamètres perpendiculaires du houppier des individus de S. birrea ont été mesurés. Pour préciser la répartition spatiale des individus de S. birrea, les données ont été collectées par cartographie des individus sur deux parcelles de 1,96 ha chacune (140 x 140 m) dans les unités « steppe arborée » et « parc agroforestier ». Les résultats montrent que les individus de S. birrea présentent une répartition spatiale aléatoire à agrégée, avec des agrégats de taille variable (environ 7 m et 25 m), en cohérence avec le mode de dispersion zoochore et barochore des fruits, et la capacité de multiplication végétative de l’espèce. Les plus fortes valeurs de densité (25,2 individus/ha), de surface terrière (1,6 m2 /ha) et de hauteur moyenne (6,9 m) ont été obtenues dans les unités des forêts classées. La forme en cloche de la distribution des classes de hauteur et des diamètres des populations traduit une meilleure représentation des classes intermédiaires, par rapport aux classes extrêmes. Par contre, la structure erratique observée dans les « zones agricoles riveraines » traduit une répartition très irré- gulière dans les classes de diamètre. Les populations de S. birrea requièrent donc une conservation plus efficace qui passera par le développement de stratégies appropriées en vue de leur restauration. Mots-clés : Sclerocarya birrea, structure spatiale, forêts classées, occupation du sol, Niger. ABSTRACT POPULATION STRUCTURE AND SPATIAL DISTRIBUTION OF SCLEROCARYA BIRREA (A. RICH.) HOCHST. STANDS IN NIGER’S SAHEL REGION The main purpose of this study was to analyse the population structure and spatial distribution of Sclerocarya birrea stands in the protected forests of Dan Kada Dodo and Dan Gado and their peripheral areas. These parameters have to be known to ensure that the stands are managed sustainably. Sample inventory plots measuring 50 x 20 m were identified by random stratified sampling in the three land use units identified (tree steppe, agroforestry sector, adjacent agricultural zones). Tree diameter at 1.30 m above the ground, total height and the two diameters perpendicular to the crown of S. birrea were measured. To define spatial distribution, S. birrea individuals were mapped in two 1.96 ha plots (140 x 140 m) in the “tree steppe” and “agroforestry sector” units. The results show that S. birrea individuals are distributed in random aggregates of varying sizes (about 7 m and 25 m), which is consistent with their zoochorous and barochorous fruit dispersal pattern and the capacity of the species for vegetative propagation. The highest densities (25.2 individuals/ha), basal areas (1.6 m2 /ha) and average heights (6.9 m) were in the protected forest sectors. The bell-shaped distribution curve for stand height and diameter classes reflects the better representation of intermediate classes than extremes. However, the erratic structure observed in the “adjacent agricultural zones” indicates a highly irregular distribution of diameter classes. We conclude that S. birrea populations require more effective conservation, with more appropriate restoration strategies to be developed. Keywords: Sclerocarya birrea, spatial structure, protected forests, land use, Niger
... Within the framework of PAMF, plantations of both exotic species and native species were established. Several investigations have been carried out on plant communities and population structures of the natural patches of WMFR (Glèlè Kakaï et al. 2009;Assogbadjo et al. 2010;Mensah et al. 2014). However, studies on the achievements of the PM approach, in terms of the contribution to forest conservation, plantation growth and management, and the improvement in standard of living of local populations, have been poorly documented. ...
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This study assessed ecological and socio-economic impacts of a participatory forest management project in the Republic of Benin. The study focused on the Wari-Maro Forest Reserve and the ‘Projet d’Aménagement des Massifs Forestiers’ five years after its completion. A forest inventory was carried out using 37 square plots of 729 m2 each to characterise the population structure of two types of plantations established: plantations with exotic species and plantations with native species. In addition, individual surveys were conducted with local households, organs of joint forest management and forestry officers to evaluate their perceptions about the participatory management of the plantations. Finally, the sustainability of the participatory management was assessed with an established rating system. Results showed that plantations with exotic species were more successful than plantations with native species. Local communities argued that they have not been involved in the plantations design but only in the implementation step and that their standards of living have decreased after the project completion. The rating system used showed that the participatory management of plantations had a short-term sustainability. The findings suggest that future projects should be designed and implemented with better participation of local communities as full partners.
... P. erinaceus participe ainsi quotidiennement à la satisfaction des besoins des populations. Mais l'absence d'une bonne connaissance de cette plante est au même titre que l'intensification de la commercialisation de leurs dérivées, l'inefficacité des plans de gestion des écosystèmes forestiers, une cause majeure de la forte régression de son peuplement (Guedje, 2003). ...
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Pterocarpus erinaceus Poir. est actuellement l’espèce spontanée des zones guinéo-soudaniennes et soudano-sahéliennes la plus exploitée au Togo. Cette étude examine le niveau de connaissance de l’espèce, les différents usages des organes de l'espèce afin d'apprécier les impacts des actions anthropiques sur le développement de ladite ressource. Pour atteindre ces objectifs, la démarche méthodologique a consisté à collecter des données quantitatives et qualitatives sur un échantillon de 2 339 répondants. Trois différents types de questionnaires, un guide d'entretien et une grille d'observation ont servi d’outils de collecte des données de base de terrain. L’espèce est très bien connue par 100% des répondants des différents groupes socioprofessionnels et sociolinguistiques. Environ 46 usages répartis dans 8 catégories d’usages ont été identifiés par les différents groupes socioculturels et socioprofessionnels. Près de 33 maux sont guéris par les organes du P. erinaceus. En matière de commercialisation, le bois de P. erinaceus est exporté sous forme de parquets finis, de madriers de palettes, et bastings. Entre 2011-2012, le Togo a exporté respectivement 18 8064 unités soit 70 m3, 10 5038 unités soit 9 440 m3, 59 86970 unité soit 70 m3 et 239 unités soit 10 m3 de ces produits. Les formes d’exploitation sévères notées, ont contribué à amplifier les effets de l’action humaine sur la dégradation de la ressource. Les différents usages des organes de l'espèce témoignent donc de l'urgence et de la nécessité de la mise en œuvre des plans d’aménagement des peuplements de P. erinaceus en vue de la sauvegarde de l'espèce.
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Chapter
Over the world, one of perspective challenges in biodiversity conservation is how to meet effective conservation of threatened species. In this frame, endangered African tree species is becoming a priority that should attract development of conservation strategies. Since biotechnology is developing rapidly as conservation strategies of biodiversity targets these last decades, it has been questioned to know (i) the current situation concerning biotechnology and endangered African tree species, (ii) the problems that prevent using of biotechnology in conservation of endangered African tree species and (iii) perspectives to help biotechnology to conserve endangered African tree species. Thus an overview on these questions showed that endangered African tree species have not taken advantages of biotechnologies strategies yet. Few biotechnologies researches based on endangered African tree species have been undertaken until now. This state of knowledge is explained by some difficulties that have been highlighted. Those difficulties concerned mostly characteristics of seeds of endangered African tree species, cost of biotechnologies strategies and bad integration of biotechnology discipline with other ones. They are preventing wide use of biotechnology strategies to conserve endangered African tree species. Considering them, some recommendations have been addressed as perspectives of conservation of endangered African tree species by biotechnology.
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Anthropogenic disturbances and climatic variations are presumed to alter species population structures. In this study,we assessed the population structure of the endangered species, Afzelia africana across gradients of climate and human disturbances. Dendrometric variables such as regeneration and tree density, mean diameter, basal area and height and stem diameter distribution were recorded at national scale in forest reserves located in three different climatic zones in Bénin. A canonical discriminant analysiswas applied to describe the species' population structure across climatic zones and disturbance levels. Relationships between the principal components (structural parameters of A. africana stands) and climatic variables and disturbance levels were assessed using Pearson correlation. Significant differences were found in the structural parameters between the disturbance levels, mostly in the Guinean zone. Structural parameters also differed significantly across the three climatic zones, with the Guinean zone recording the highest values. The effects of disturbance levels on structural parameters depend on the climatic zone, and vice versa. The results imply an interaction between climatic zones and disturbance levels. In the Guinean zone, the tallest and biggest trees were found at the low disturbance level. However, along the climatic gradient (towards drier regions), trees were shorter and smaller irrespective of disturbance level. Further, the tallest and biggest trees were found at lower altitudes.
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Indigenous woody species are important natural resources in West African savannas. Information about their population structures and response to human impact, particularly land use, however, is scarce. In this study, we explored (1) the effect of land use on the population structure of woody savanna species; and (2) searched for species with similar population structures related to comparable ecological preferences. Using generalized linear models, we separately analyzed the size-class distribution (SCD) of 30 species to reveal the influence of three land cover types (non-arable land, fallows, and protected areas) on population structures. Generalized linear models were applied to identify comparable population structures of species with similar ecological preferences. We were able to identify five groups for shrub species and four groups for tree species with different population structures and comparable ecological preferences. In terms of human impact, we detected four groups of species responding similarly to land use. Especially for trees, we found a strong influence of local land use on SCD and hence, population structures. The SCD of shrub species tends to be more related to species' ecological preferences. Some of the shrub species may be characterized as ubiquitous species as their SCD is neither related to land use nor ecological preferences, indicating a high tolerance to disturbance. The observed results have implications on local woody species composition in relation to land use. According to this, we propose focusing on trees when developing appropriate local land use management strategies.
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Research was carried out on four threatened tree species across north and south Sudanian phytogeographical zones in Burkina Faso. A quantitative inventory of regeneration populations was completed and sapling dynamics were monitored through surveys of survival and growth in permanent plots. Laboratory and nursery experiments were carried out to test germination and the performance of transplanted seedlings. Results revealed difficulties that saplings faced during their development. In natural stands of Sterculia setigera and Afzelia africana, saplings were rare or irregularly distributed. A greater number of individuals of Bombax costatum were observed, which was the only species with significant density variation between phytogeographical zones (p = 0.021). Size class showed irregular population structures. A high mortality between the first and second year, followed by a stabilization trend, was observed. The initial height of saplings was highly correlated to their survival rate. The rate of new sapling spontaneous recruitment was better in Bombax costatum and Boswellia dalzielii stands, but heir growth was unpredictable in all species. Most saplings grew from lignotubers and root suckers; however, the potential for sexual reproduction was good. Sterculia setigera and Bombax costatum seedlings showed potential for use in silviculture, as evidenced by the fact that both showed high post-transplantation rates of survival and growth.
Article
A study was carried out in the Lama forest reserve of Benin to characterize the habitat of Afzelia africana Sm., an endangered multipurpose tree species (found in African humid, dry forests and woodlands), in order to define a sustainable management strategy for its conservation. An estimation of species density was done on 100 square plots of 1 ha each, while tree height and dbh of all the species were measured on subplots of 50 m � 30 m within the 1 ha plots. The regenerations of A. africana (dbh < 10 cm) were counted in the diagonal quadrats of the principal plots. Presence–absence data of the species was subjected to multidimensional scaling and results showed four vegetation communities including: young fallow, old fallow, typical dense forest and degraded dense forest. Significant differences were noted between the four communities with respect to dendrometric parameters of the species. High values of these parameters were noted for the species in typical dense forest (5.2 stems/ha, 66.7 cm, 17.9 m, 7.9 m2/ha and 38.8% for the tree-density, the mean diameter, the mean height, basal area and basal area contribution of the species, respectively) whereas the lowest values were obtained for the old preforest fallow as far as the mean diameter (59.7 cm), the mean height (15.7 m) and the basal area contribution (27.7%) of the species were concerned. In general, the basal area of A. africana in the over vegetation types was less than 3 m2/ha. No A. africana tree was found in the young preforest fallow while more than 80% of A. africana trees were found in the typical dense forest community. Stem diameter and height structures of the species in all the four communities showed a left dissymmetric Gaussian shape and were well adjusted to Weibull distribution.
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In southern African savannas, bush encroachment is a major problem for range managers. However, little is understood of the actual regeneration processes leading to it, and in particular the role of soil seed banks. The horizontal (between microsites) and vertical (with depth in litter and soil) distribution of soil seed banks of the microphyllous woody species, Acacia tortilis, A. nilotica and Dichrostachys cinerea (all legumes of the Mimosoideae), were quantified in an area with low intensity grazing (reserve), and a bordering cattle farm with high intensity grazing (farm). Species differed in seed bank densities between microsites and sites. Seed densities for all species were highest below parent tree canopies and decreased with distance beyond the canopy, and with soil depth. D. cinerea had the smallest seed bank associated with parent trees, particularly on the farm (8 vs. 1643 seeds/tree on the reserve), A. tortilis had the largest (6357, 31910), with A. nilotica intermediate (1789, 1906). The proportion of current (recently fallen) versus old (1year old) seeds differed between species and sites. These species form at least short-term persistent seed banks with the old seeds largely representing the persistent seed bank. Seed densities in the open (inter-canopy) and those dispersed under either of the other two (non-parental) study species were much lower than those associated with parent trees. The latter were mostly found under the acacias (single-stemmed) rather than D. cinerea (multistemmed). Total seed store per parent plant increased with plant size (best fits were mostly power curves of canopy area). A large proportion of intact seeds were viable, namely 81–84% for A. tortilis, 68–77% for A. nilotica and 63–78% for D. cinerea, with no differences between sites. Viability tended to increase with depth of burial, except for A. nilotica seeds at the 3–5cm depths on the farm. At the landscape scale there were 1.5 million and 140000 A. tortilis seeds/ha on the reserve and farm respectively, with corresponding values of 2000 and 31000 for D. cinerea, and 23000 and 86000 for A. nilotica.
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