Distribution des épiphytes de Côte d’Ivoire : effets des zones phytogéographiques et des variations pluviométriques

La gestion de la diversité biologique se présente comme un défi majeur du fait des problèmes liés à la connaissance et à la préservation des ressources biologiques. Cette étude est une contribution à une meilleure connaissance de la diversité végétale de la Côte d’Ivoire à travers celles des épiphytes. Les espèces épiphytiques présentes dans les Herbiers du CNF (UCJ) et du CSRS ont été recensées. Ces informations ont été complétées par une revue bibliographique sur les épiphytes de Côte d’Ivoire. Les données recueillies ont été triées et corrigées. Les noms et les coordonnées géographiques ont été vérifiés. La compilation des listes corrigées a permis d’avoir un nombre d’occurrences des espèces recensées en Côte d’Ivoire avec la position géographique pour chaque récolte. Ces travaux présentent 380 espèces épiphytiques qui se repartissent entre 110 genres, 32 familles et 21 ordres. Les espèces les plus récoltées sont : Culcasia scandens (209 occurrences), Culcasia angolensis (180 occurrences), Piper guineense (91 occurrences), Cercestis afzelii (86 occurrences) et Bulbophyllum falcatum (75 occurrences). On rencontre des espèces épiphytiques sur tout le territoire ivoirien. Néanmoins, on note de fortes concentrations des récoltes dans le Sud et l’Ouest montagneux. Les modélisations et les cartographies effectuées permettent d’observer que l’espèce Culcasia angolensis qui se retrouve uniquement dans les espaces de forêt est certainement plus sensible au stress hydrique. On peut donc dire que Culcasia angolensis ne supporte pas une longue dessiccation comparativement à Culcasia scandens.Mots-clés : épiphytes, maxent, composition floristique. Distribution of the epiphytes listed in Côte d'Ivoire according to the phyto-geographical zones and rainfall variations'The management of biological diversity is presented as a major challenge because of the problems involved in the knowledge and the safeguarding of the biological resources. This study is a contribution with a better knowledge of plant diversity of the Côte d'Ivoire through those of the epiphytes. The epiphytic species present in the Herbarium of the CNF (UCJ) and the CSRS were listed. This information was supplemented by a bibliographical review on the epiphytes of Côte d'Ivoire. The data collected were sorted and corrected. The names and geographical co-ordinates were checked. The compilation of the corrected lists conducted to census the occurred epiphytes listed in Côte d'Ivoire. A total number of 380 epiphytic species were recorded. They belonged to 110 genera, 32 families and 21 orders. The most collected species were: Culcasia scandens (209 occurrences), Culcasia angolensis (180 occurrences), Piper guineense (91 occurrences), Cercestis afzelii (86 occurrences) and Bulbophyllum falcatum (75 occurrences). Epiphytic species are met in the entire territory of Côte d’Ivoire with a strong concentration in the South and mountainous west region. Modellings and mapping carried out allow us to observe that the species Culcasia angolensis which is found only forests is certainly more sensitive to the hydrous stress. One can thus say that Culcasia angolensis does not support a long desiccation compared to Culcasia scandensKeywords: epiphytes, Maxent, plant species composition

Aboveground forest biomass varies across continents, ecological zones and successional stages: refined IPCC default values for tropical and subtropical forests

For monitoring and reporting forest carbon stocks and fluxes, many countries in the tropics and subtropics rely on default values of forest aboveground biomass (AGB) from the Intergovernmental Panel on Climate Change (IPCC) guidelines for National Greenhouse Gas (GHG) Inventories. Default IPCC forest AGB values originated from 2006, and are relatively crude estimates of average values per continent and ecological zone. The 2006 default values were based on limited plot data available at the time, methods for their derivation were not fully clear, and no distinction between successional stages was made. As part of the 2019 Refinement to the 2006 IPCC Guidelines for GHG Inventories, we updated the default AGB values for tropical and subtropical forests based on AGB data from >25 000 plots in natural forests and a global AGB map where no plot data were available. We calculated refined AGB default values per continent, ecological zone, and successional stage, and provided a measure of uncertainty. AGB in tropical and subtropical forests varies by an order of magnitude across continents, ecological zones, and successional stage. Our refined default values generally reflect the climatic gradients in the tropics, with more AGB in wetter areas. AGB is generally higher in old-growth than in secondary forests, and higher in older secondary (regrowth >20 years old and degraded/logged forests) than in young secondary forests (20 years old). While refined default values for tropical old-growth forest are largely similar to the previous 2006 default values, the new default values are 4.0-7.7-fold lower for young secondary forests. Thus, the refined values will strongly alter estimated carbon stocks and fluxes, and emphasize the critical importance of old-growth forest conservation. We provide a reproducible approach to facilitate future refinements and encourage targeted efforts to establish permanent plots in areas with data gaps

Aboveground forest biomass varies across continents, ecological zones and successional stages: refined IPCC default values for tropical and subtropical forests

For monitoring and reporting forest carbon stocks and fluxes, many countries in the tropics and subtropics rely on default values of forest aboveground biomass (AGB) from the Intergovernmental Panel on Climate Change (IPCC) guidelines for National Greenhouse Gas (GHG) Inventories. Default IPCC forest AGB values originated from 2006, and are relatively crude estimates of average values per continent and ecological zone. The 2006 default values were based on limited plot data available at the time, methods for their derivation were not fully clear, and no distinction between successional stages was made. As part of the 2019 Refinement to the 2006 IPCC Guidelines for GHG Inventories, we updated the default AGB values for tropical and subtropical forests based on AGB data from >25 000 plots in natural forests and a global AGB map where no plot data were available. We calculated refined AGB default values per continent, ecological zone, and successional stage, and provided a measure of uncertainty. AGB in tropical and subtropical forests varies by an order of magnitude across continents, ecological zones, and successional stage. Our refined default values generally reflect the climatic gradients in the tropics, with more AGB in wetter areas. AGB is generally higher in old-growth than in secondary forests, and higher in older secondary (regrowth >20 years old and degraded/logged forests) than in young secondary forests (⩽20 years old). While refined default values for tropical old-growth forest are largely similar to the previous 2006 default values, the new default values are 4.0–7.7-fold lower for young secondary forests. Thus, the refined values will strongly alter estimated carbon stocks and fluxes, and emphasize the critical importance of old-growth forest conservation. We provide a reproducible approach to facilitate future refinements and encourage targeted efforts to establish permanent plots in areas with data gaps

Evenness mediates the global relationship between forest productivity and richness

1. Biodiversity is an important component of natural ecosystems, with higher species richness often correlating with an increase in ecosystem productivity. Yet, this relationship varies substantially across environments, typically becoming less pronounced at high levels of species richness. However, species richness alone cannot reflect all important properties of a community, including community evenness, which may mediate the relationship between biodiversity and productivity. If the evenness of a community correlates negatively with richness across forests globally, then a greater number of species may not always increase overall diversity and productivity of the system. Theoretical work and local empirical studies have shown that the effect of evenness on ecosystem functioning may be especially strong at high richness levels, yet the consistency of this remains untested at a global scale. 2. Here, we used a dataset of forests from across the globe, which includes composition, biomass accumulation and net primary productivity, to explore whether productivity correlates with community evenness and richness in a way that evenness appears to buffer the effect of richness. Specifically, we evaluated whether low levels of evenness in speciose communities correlate with the attenuation of the richness–productivity relationship. 3. We found that tree species richness and evenness are negatively correlated across forests globally, with highly speciose forests typically comprising a few dominant and many rare species. Furthermore, we found that the correlation between diversity and productivity changes with evenness: at low richness, uneven communities are more productive, while at high richness, even communities are more productive. 4. Synthesis. Collectively, these results demonstrate that evenness is an integral component of the relationship between biodiversity and productivity, and that the attenuating effect of richness on forest productivity might be partly explained by low evenness in speciose communities. Productivity generally increases with species richness, until reduced evenness limits the overall increases in community diversity. Our research suggests that evenness is a fundamental component of biodiversity–ecosystem function relationships, and is of critical importance for guiding conservation and sustainable ecosystem management decisions

Diversité végétale et valeur de conservation pour la Biodiversité du Parc National du Mont Péko, une aire protégée, menacée de disparition en Côte d’Ivoire.

Objectif : Cette étude vise à caractériser la végétation du Parc National du Mont Péko en termes de composition floristique et de présence d’espèces à statut particulier ainsi que la valeur du parc pour la conservation.Méthodologie et résultats : Un échantillonnage de la végétation a été conduit dans trois zones du Parc National du Mont Péko (PNMP), en Côte d’Ivoire. Quinze placettes de 400 m2 ont été mises en place. La flore est riche de 384 espèces appartenant à 88 familles. Les familles les plus riches en espèces sont celles des Fabaceae, des Rubiaceae, des Malvaceae et des Moraceae. Parmi les espèces recensées, 74 sont endémiques, rares et menacées d’extinction au plan national, régional ou international. L’étude a montré que quatre des principales valeurs pour la conservation de la biodiversité sont atteintes par la forêt du parc.Conclusion et application : Cette étude met en évidence l’importance de la sauvegarde du Parc National du Mont Péko, une aire protégée montagneuse, fragile et menacée de disparition. Aussi, la présence de nombreuses espèces à statut particulier justifie l’inclusion du parc dans le « Guinean Forests of West Africa Hotspot» d'importance mondiale pour leur biodiversité. Les différentes caractéristiques du parc révélées par cette étude sont des connaissances nécessaires aux plans de gestion.Mots clés : Biodiversité, valeur de conservation, Mont Péko, Côte d’Ivoir

Diversité floristique et dégré d\'infestation par les mauvaises herbes des agroécosystèmes environnant la forêt classée de sanaimbo, dans le Centre-Est de la Côte d\'Ivoire

La caractérisation des enherbements des parcelles agricoles environnant la forêt classée de Sanaimbo a été réalisée à partir de 310 relevés phyto-écologiques. La flore adventice comprend 398 espèces. Cellesci sont classées en fonction de leur fréquence et de leur abondance. L\'analyse floristique quantitative montre que les espèces les plus fréquentes sont Chromolaena odorata, Panicum laxum, Pouzolzia guineensis, Solanum erianthum, Laportea aestuans, Spigelia anthelmia et Mariscus cylindristachyus, et que les mauvaises herbes qui posent des problèmes majeurs d\'infestation dans les parcelles agricoles, sont Chromolaena odorata, Euphorbia heterophylla, Croton hirtus et Ageratum conyzoides. Mais la plus nuisible reste Chromolaena odorata.Characterization of weed communities in the fields surrounding the classified forest of Sanaimbo was done through 310 phyto-ecological plots. The weeds flora is made of 398 species. They are listed according to their frequency and abundance. Quantitative floristic analysis shows that the more frequent species are Chromolaena odorata, Panicum laxum, Pouzolzia guineensis, Solanum erianthum, Lapotea aestuens, Spigelia anthelmia and Mariscus cylindristachyus and the weeds that more cause damage are Chromolaena odorata, Euphorbia heterophylla, Croton hirtus and Ageratum conyzoides. But the most noxious weed is Chromolaena odorata. Keywords: Mauvaise herbe, diversité floristique, degré infestation, forêt classée de Sanaimbo, Côte d\'Ivoire.Agronomie Africaine Vol. 20 (1) 2008: pp. 13-2

Dynamique d'expansion des cacaoyères dans les zones de contact forêt-savane : cas de la sous-préfecture de Kokumbo (Centre de la Côte d'Ivoire)

Cocoa Expansion Dynamics in the Forest-Savanna Contact Zones: Case Study of the Sub-prefecture of Kokumbo (Côte d'Ivoire). In Ivory Coast, forests-savannah transition areas have been considered from the 1970s as unfavorable to cocoa cultivation. In recent years, however, there has been a comeback to the cocoa economy in these areas. This study carried out in the sub-prefecture of Kokumbo, aimed to map and to follows the spatial and temporal evolution of this crop using Landsat images of 1990, 2002 and 2016. In order to better understand the fundamentals of the peasant practices, surveys were carried out in different villages in the area. Treatment shows that the influence of cocoa culture is becoming increasingly important in the region. This cocoa crop is set up to the detriment of forests and savannahs, which have lost 25% and 58.1% of their initial area respectively. The surveys identified four types of cocoa farms, of which 65% of the plots were created between 2002 and 2014. Facing this relatively recent expansion, the issue of the sustainability of cocoa production systems in this region arises. Their agronomic and economic performances and their value for biodiversity conservation should be analyzed in future studies

Evenness mediates the global relationship between forest productivity and richness

Funder: DOB Ecology1. Biodiversity is an important component of natural ecosystems, with higher species richness often correlating with an increase in ecosystem productivity. Yet, this relationship varies substantially across environments, typically becoming less pronounced at high levels of species richness. However, species richness alone cannot reflect all important properties of a community, including community evenness, which may mediate the relationship between biodiversity and productivity. If the evenness of a community correlates negatively with richness across forests globally, then a greater number of species may not always increase overall diversity and productivity of the system. Theoretical work and local empirical studies have shown that the effect of evenness on ecosystem functioning may be especially strong at high richness levels, yet the consistency of this remains untested at a global scale. 2. Here, we used a dataset of forests from across the globe, which includes composition, biomass accumulation and net primary productivity, to explore whether productivity correlates with community evenness and richness in a way that evenness appears to buffer the effect of richness. Specifically, we evaluated whether low levels of evenness in speciose communities correlate with the attenuation of the richness–productivity relationship. 3. We found that tree species richness and evenness are negatively correlated across forests globally, with highly speciose forests typically comprising a few dominant and many rare species. Furthermore, we found that the correlation between diversity and productivity changes with evenness: at low richness, uneven communities are more productive, while at high richness, even communities are more productive. 4. Synthesis. Collectively, these results demonstrate that evenness is an integral component of the relationship between biodiversity and productivity, and that the attenuating effect of richness on forest productivity might be partly explained by low evenness in speciose communities. Productivity generally increases with species richness, until reduced evenness limits the overall increases in community diversity. Our research suggests that evenness is a fundamental component of biodiversity–ecosystem function relationships, and is of critical importance for guiding conservation and sustainable ecosystem management decisions