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Due to rapid population growth and economic activity, disposal of solid and liquid waste has become a major problem in and around Serekunda (Gambia). The solid waste collected in the Kanifing Municipal Council, which is the most densely populated municipality in the Gambia, is dumped openly on the Kotu landfill site. The only technique used to dispose of this waste at the site is open burning. As for the liquid waste collected in households and industries, it is discharged in open air at several sites and in rivers. All of this constitutes a significant environmental and health hazard. They are sources of air, soil and groundwater pollution, and acute respiratory infections (AIRs). Despite this, no recycling technique for this waste, which is concerned with the environment and human well-being, has been developed by the Gambian Government so far. However, this waste can be renewed and used as energy in several areas, including agriculture and households. This study, carried out as part of the research themes of the West African Institute for Research and Development (WARDI), aims to identify technologies that can be used to recycle waste for irrigation, compost, and energy.

Located in the south of Senegal, the Upper-Casamance (present-day Kolda region) has a strong vegetation dynamic mainly due to the clearing of land for agricultural needs, bush fires, population growth and uncontrolled logging. In such a situation, mapping and quantification of changes in vegetation cover become relevant for a more rational and sustainable management of plant resources, but also for the achievement of the Sustainable Development Goals. This study aims to detect the degradation and regeneration of vegetation cover during the last two decades in Upper-Casamance. It is based on an analysis of the trends of MODIS NDVI images time series acquired over the period 2000-2018, on a land cover and use changes (LULCC) maps established from Landsat images (ETM+ 1999 and OLI 2018), and a joint analysis of NDVIand LULCC trends. Data processing is based on the calculation of the Kendall correlation (τ) and the p significance test at the 10% threshold, and on a multistage unsupervised classification, respectively. The study shows significant changes in land cover and land use, including conversion from forest to savannah (13.5%), and from savannah to crop and habitat areas (7.9%). Significant negative trends in NDVI (related to forest-savanna conversion and forest-cropping and habitat areas) are observed in 2.1% of the study area and indicate vegetation degradation especially along the border with Gambia, on the Pata-Ndorna axis, in the centre of the study area, and around Medina Gounass. On the other hand, significant positive trends on 1.8% of the study area are evidence of regeneration in the south and are linked to the conversion ofcultivated areas into savanna and forest. Joint analysis of NDVI and LULCC trends indicated significant degradation in south of Kerewane and Niaming, on the Ndorna-Pata axis, around Medina Gounass, and towards Saré Coly; and significant regeneration at the northeast border, north of Mampatim, to the south towards Bagadadji and Medina El Hadji, and between Linkering-Paroumba. This analysis also revealed that the two sources of data (NDVI et Landsat) are spatially consistent and that most of the trends in vegetation productivity are explained by changes in land use and not by climate., Cette étude vise à détecter et cartographier la dégradation et la régénération de la couverture végétale durant ces deux dernières décennies en Haute-Casamance, située dans le sud du Sénégal. Elle s'appuie sur l'analyse des tendances de séries temporelles d'images MODIS NDVI acquises sur la période 2000-2018, sur la cartographie des changements d'occupation et d'utilisation des sols (LULCC) faite à partir d'images Landsat (ETM+ 1999 et OLI 2018), et sur une analyse conjointe des tendances de NDVI et LULCC. L'étude a révélé d'importants changements en termes d'occupation et d'utilisation des sols, notamment la conversion de la forêt à la savane (13,5 %), et de la savane aux zones de culture et d'habitat (7,9 %). Des tendances négatives significatives (p

Context and background In the classified and managed forests of Upper-Casamance, the vegetation cover is undergoing significant changes. The result is a strong tendency to convert forest into savannah and cultivation areas, which goes against the policy of classification and management of forests. Objectives This study analyzes the changes in vegetation cover in classified and managed forests in Upper-Casamance between 1965 and 2018 to help politicians in their decision-making. Methodology It focused on six forest areas that reflect the evolution of plant cover in Haute-Casamance, including three classified (Pata, Kantora and Dabo) and three developed (Saré Bidji, Medina Salam Dingha and Bonconto). The approach used is based on a visual interpretation, from Corona 1965 and Sentinel 2 imagery from 2018, of land use trends and vegetation changes. Results The results indicated a great variability in plant cover depending on the area, the geographical position of these perimeters in the study area, and anthropogenic pressure. With the exception of the classified forest of Dabo located in the south, the forests of the classified domain (Pata and Kantora which are exposed in the north) have experienced a greater conversion of plant cover. They are also more affected by human actions than the forests in the managed area. Likewise, the managed forest of Medina Salam Dingha, located a little further north, has undergone a greater conversion of vegetation than those reserved a little more in the south. Moreover, in the managed forest of Bonconto, the tendency is to regenerate the vegetation cover. These different trends in vegetation raise the issue of the current status of certain classified forests and the importance of forest management.

Situee en zone frontaliere entre le Senegal et la Gambie, la partie nord de la Haute-Casamance (actuelle region de Kolda) fait l’objet d’une importante deforestation. Les modifications qui y sont observees resultent, pour l’essentiel, de la destruction des massifs forestiers pour l’agriculture et des coupes massives de bois a destination, surtout, de la Gambie voisine. C’est dans ce contexte que notre etude se propose d’analyser la dynamique de la deforestation dans la zone frontaliere nord de la Haute-Casamance, ainsi que les principaux facteurs explicatifs. L’etude est basee sur une cartographie diachronique de l’occupation des sols entre 1987 et 2018 a partir des images satellitaires Landsat (TM 1987, ETM+ 1999, TM 2010 et OLI 2018), sur le calcul des Indices Standardises des Precipitations (ISP), et sur les travaux de terrain. Les resultats indiquent, qu’entre 1987 et 2018, la foret claire et la savane boisee ont perdu respectivement 66 485,5 ha et 36 470,6 ha de leur superficie en faveur principalement des zones de culture qui ont augmente de 71 995,9 ha, et de la savane arboree a arbustive qui a augmente de 48 711,6 ha. L’analyse des principaux facteurs a l’origine de la deforestation a montre qu’il s’agit des defrichements pour les besoins agricoles, l’augmentation de la population, les coupes non controlees de bois, et l’evolution des conditions pluviometriques.

Les paysages forestiers du Sud du Sénégal, particulièrement dans le département de Vélingara, font de plus en plus l'objet de déforestation. Il en résulte une forte tendance à leur "savanisation", d'où la préoccupation majeure des autorités sénégalaises à prendre le problème en charge. Devant une telle situation, l'étude de la dynamique spatio-temporelle du couvert végétal devient pertinente pour une gestion durable des ressources forestières. C'est l'objet de cette étude qui vise à analyser l'évolution des paysages forestiers du département de Vélingara et les facteurs de leur dynamique. La méthodologie adoptée s'appuie sur l'exploitation d'images du satellite Landsat acquises en 1987, 2003 et 2018, et sur des travaux de terrain. Les résultats indiquent une "savanisation" liée à une importante déforestation et à la progression des surfaces agricoles au nord et au centre du département. Cette évolution est d'autant plus accentuée d'est en ouest. Entre 1987 et 2003, la forêt a perdu 93642 ha de sa superficie (soit 17 %), contre une progression de la savane (+59717 ha) et des zones de culture (+26380 ha) associées aux zones d'habitat et aux sols nus. La période 2003-2018 est marquée par la régression de la forêt et de la savane; respectivement de 34149 et de 6108 ha, au profit d'une augmentation importante des surfaces agricoles (+35055 ha) et des zones d'habitat (+10466 ha). Cette dynamique résulte de la combinaison de plusieurs facteurs : défrichements pour les besoins agricoles, feux de brousse, augmentation de la population, coupes non contrôlées de bois, évolution des conditions pluviométriques, entre autres. Forest landscapes located of southern Senegal, particularly in the department of Velingara, are increasingly subject to deforestation. As a result, there is a strong tendency to "savanise" them, hence the Senegalese authorities' major concern to take the problem in charge. In such a situation, the study of the spatio-temporal dynamics of the vegetation cover becomes relevant for a sustainable management of the forest resources. This is the purpose of this study which aims to analyze the evolution of the forest landscapes of the department of Velingara and the factors of their dynamics. The methodology adopted is based on the exploitation of Landsat satellite imagery acquired in 1987, 2003 and 2018, and on field work. The results indicate a "savanization" linked to a significant deforestation and a growth of agricultural areas in the north and center of the department. This evolution is all the more marked according to an east-west gradient. Between 1987 and 2003, the forest lost 93642 ha of its area (17 %), against a progression of the savannah (+59717 ha) and cultivation areas (+26380 ha) associated with the zones of habitat and bare grounds. The period 2003-2018 is marked by the regression of the forest and the savannah; 34149 and 6108 ha respectively, to the benefit of a significant increase in agricultural area (+35055 ha) and the habitats (+10466 ha). This dynamic results from the combination of several factors: clearing for agricultural needs, bush fires, population increase, uncontrolled logging, changes in rainfall conditions, among others.

En Basse-Casamance, la mangrove constitue un écosystème particulier qui abrite de nombreuses ressources et reste le siège des principales activités rurales. Dans la zone d’Oussouye, cette mangrove a connu une régression importante au cours des décennies 1970 et 1980. L’étude de sa dynamique spatio-temporelle, à partir des outils de la géomatique couplés à des enquêtes de terrain, a permis d’appréhender son déclin, entre 1972 et 1994 de -42 % ; et son évolution positive de +22,44 % entre 1994-2018. Les facteurs à l’origine de la régression durant les années 70 et 80 sont principalement le déficit pluviométrique avec comme conséquences la salinisation et l’acidification des terres, et la faiblesse de la régénération naturelle. L’étude a aussi montré que les actions anthropiques telles que la coupe du bois pour diverses raisons et des racines échasses ont longtemps porté préjudice aux écosystèmes de mangrove. La reprise constatée au cours des dernières décennies est à replacer dans le contexte du retour de la pluviométrie à une situation meilleure et à la prise de conscience des populations du rôle stratégique et important de la mangrove.

Du fait de sa position géographique (proximité avec l’océan Atlantique), de la richesse de ses écosystèmes (cours d’eau à prédominance de mangrove) et de l’importance des activités socio-économiques (pêche, riziculture, tourisme, etc.), l’Afrique de l’Ouest demeure une des régions les plus importantes du monde en termes de biodiversité. Elle est parmi les régions les plus touchées par les changements environnementaux et les dynamiques rurales. En s’appuyant, pour l’essentiel, sur les résultats obtenus dans le cadre du consortium Patrimoines et Territoires de l’Eau (PATEO), ce travail analyse la vulnérabilité et la résilience des socio-écosystèmes littoraux d’Afrique de l’Ouest en termes d’état de connaissances actuelles et s’interroge sur leur devenir. Les résultats ont révélé des mutations environnementales et socio-économiques relativement importantes, positives ou négatives, témoignant d’une forte dynamique des zones littorales ouest-africaines. Ces changements reposent sur diverses forces externes et internes qui s’exercent sur les écosystèmes et les sociétés, surtout rurales, et les font évoluer depuis les années 1970. Dans ce contexte, sociétés et milieux sont soumis aux mêmes aléas, mais se sont montrés plus ou moins vulnérables ou résilients en fonction de leur degré de dépendance à l’extérieur. Cette situation influe grandement sur les politiques publiques d’aménagement du territoire. Due to its geographical position (proximity to the Atlantic Ocean), the richness of its ecosystems (predominantly mangrove rivers) and the importance of socio-economic activities (fishing, rice growing, tourism, etc.), West Africa remains one of the most important regions in the world. It is among the regions most affected by environmental changes and rural dynamics. Basically based on the results obtained within the framework of the Water Heritage and Territories consortium (PATEO), this work analyzes the vulnerability and resilience of coastal socio-ecosystems in West Africa in terms of the state of current knowledge and questions their future. The results revealed relatively significant environmental and socio-economic changes, positive or negative, testifying to the strong dynamics of West African coastal areas. These changes are based on various external and internal forces exerted on ecosystems and societies, especially rural ones, and have been causing them to evolve since the 1970s. In this context, societies and environments are subject to the same hazards, but have shown themselves to be more or less vulnerable or resilient depending on their degree of dependence on the outside. This situation greatly influences public land use planning policies.

Cette étude propose une approche cartographique et statistique qui permet de calculer les taux de variation historique du trait de côte avec le plug-in DSAS dans la partie nord de l’estuaire de la Casamance au Sénégal. Pour ce faire, une méthode statistique d’extrapolation et de calcul de tendances est mise en place, basée sur le traitement des images satellitaires Landsat acquises entre 2004 et 2019. Cette méthode a permis d’obtenir une représentation cartographique et graphique des résultats statistiques sur l’évolution du trait de côte de l’estuaire nord de la Casamance. This article offers a cartographical and statistical approach to calculating rate variance of coastlines over time using the DSAS plugin; using the northern part of Casamance estuary in Senegal as the case study. To do so, we established a method to stasticially extrapolate and calculate trends, based on the analyis of Landsat satellite images taken between 2004 and 2019. We were thus able to obtain a cartographic and graphic representation of statistical results concerned with the changing coastline of the Casamance estuary. Este trabajo estudia, mediante una aproximación cartográfica y estadística, la evolución de la línea costera en la parte norte del estuario de Casamance en Senegal utilizando el programa informático DSAS l. Para ello se usa un método estadístico de extrapolación y cálculo de tendencias procesando las imágenes satélite Landsat entre 2004 y 2019. Este procedimiento permitió representar gráfica y cartográficamente las estadísticas de la evolución litoral del estuario norte de Casamance.

In The Gambia, the vegetation cover has undergone significant changes over the past two decades. To assist policy decision-making, this study seeks to detect trends in changes over the past two decades using a time series of NDVI MODIS images. The methodological approach is based on the calculation of the correlation of Kendall (τ) associated with the p-significance test at the 10 % threshold. The results showed a trend of increasing vegetation productivity during the decade 2000-2009 (98.37% of the study area) in almost all administrative regions. This trend is more significant along the river. In contrast, during the decade 2010-2019, it was noted overall significant downward trend in productivity (44.01% of The Gambia) in all administrative regions except West Coast Region and Banjul, however not significant. The result showed that, over the whole period (2000-2019), 61.86% of the national territory was characterized by a positive trend and 38.14% by a negative trend; and that the significant positive trend percentage is 10%, the significant negative trend percentage is 4%. Significant positive trends are observed much more along the river and central of the Central River Region; significant negative trends are observed mainly in the western part of West Coast Region and Banjul, at the eastern end of the North Bank Region and in the Upper River Region. En Gambie, la couverture végétale connaît d’importantes modifications depuis les deux dernières décennies. Pour aider les politiques dans leur prise de décision, cette étude cherche à détecter les tendances des changements au cours de cette période à l’aide d’une série temporelle d’images MODIS NDVI. L’approche méthodologique est basée sur le calcul de la corrélation de Kendall (τ) associé au test de significativité de p au seuil de 10 %. Les résultats ont montré une tendance à l’augmentation de la productivité de la végétation durant la décennie 2000-2009 (98,37 % de la zone d’étude) dans quasiment toutes les régions administratives. Cette tendance est plus significative le long du fleuve. Par contre, durant la décennie 2010-2019, on a noté globalement d’importantes tendances à la baisse de la productivité (44,01 % de la Gambie) dans toutes les régions administratives excepté la West Coast Region et Banjul, toutefois non significatives. à l’échelle de toute la période étudiée (2000-2019), 61,86 % du territoire national est marqué par une tendance positive et 38,14 % par une tendance négative. Le pourcentage de tendance positive significative est de 10 %, celui significativement négatif de 4 %. Les tendances positives significatives sont le plus souvent observées le long du fleuve et dans le centre de la Central River Region, celles significativement négatives principalement dans la partie ouest de la West Coast Region et de Banjul, à l’extrémité Est de la North Bank Region et de la Upper River Region.

Like other regions of Guinea Bissau, the economy of the Cacheu region is not very diversified and is dominated by cashew nut cultivation. As the country's leading production zone, with more than 30% of the national cashew nut production, the region has seen the disappearance of a large part of its natural ecosystems, especially the Elaeis guineensis parklands, despite their socio-economic importance. It is in this logic that this study is devoted to the analysis of the dynamics of the Elaeis guineensis parklands in the Cacheu region over the last fifteen years. To do this, terroir transects and mapping were carried out in order to identify and see the evolution of the landscape units. Surveys on the dynamics of the parklands and other landscape units have been carried out. The combination of these methods revealed a strong disappearance of Elaeis guineensis parklands and natural vegetation. Between 2003 and 2018, an average increase of 224 ha of cashew plantation by village terroir was noted, already causing the disappearance of 153.26 ha of Elaeis guineensis parklands on average. The main cause of this disappearance is the uncontrolled expansion of cashew nut plantations. In addition to this, there are many cuts of palm tree for house construction, habitat expansion, bad exploitation practices and climate deterioration. This pressure on Elaeis guineensis parklands is gradually leading them to disappear in favour of cashew nut monoculture. It is for this purpose that special attention is being paid to these ecosystems, which are of paramount importance to the livelihood of the local population.

In order to study the evolution of land use and the changes in land cover in Upper Casamance, from Landsat images acquired in 1987 and 2018, we used a method of multistage unsupervised classification. Recently developed to mapping and quantification of vegetation land cover changes in West-African coastal, this method is based on the following stages: first classification (K-means) over 15 classes, interpretation of the spectral signatures of the resulting classes followed by reclassification according to the chosen nomenclature, creation of thematic masks, classifications on masks, and finally reclassification. With the only difference, our study aims also to contribute, methodologically, to the knowledge of the spectral profiles of plant formation types. On a thematic level, the results show that between 1987 and 2018, forest areas decreased by 377,118.7 ha (or 27.4%), while wooded areas and agricultural and soil surfaces increased by 263,172.4 ha (or 19.1%) and 1560 75.5 ha (11.3%). In terms of change, deforestation by increasing agricultural and soil surfaces is noted along the border with the Gambia, savanization and anthropization is noted along the central part, and stability of forest surfaces followed by a slight increase in savannas and agricultural and soil surfaces is noted in the south.

In the village soil of Thiobon in lower Casamance (southern Senegal), site being established as Marine Protected Area (MPA), the main activities of the population (rice growing, harvesting of fish products, salt production, …), happens in mangrove zone. These mobilize the population for several months in the year. This mangrove ecosystem, vulnerable and fragile, has undergone profound changes since the 1960s under the combined actions of rainfull variability and main. This study proposes to analyze the spatio-temporal dynamics of Thiobon mangrove. The method used is based on the processing and analysis of satellite data (Landsat imagery acquired in 1972, 1986, 2000 and 2017), rainfall data (1960 to 2017), and on the perception of populations of change in their terroir (field investigation). Map results indicate an overall decline on 52% in mangrove area in tanne during drought years (1970 to the late 1990s). During 2000–2017, characterized by the almost normal return of the rainfall and activities of reforestation done by the local population, about 69% of the mangrove areas lost between 1972 and 2000 regenerated. This dynamic is the result of external and internal forces exerted on this ecosystem and evolve since the early 1970s.