RESUMELa conservation et la gestion rationnelle des aires protégées requièrent des études préalables de caractérisations écologique et floristique. Dans cette optique, il a été envisagé des prospections de base de la flore ligneuse et du sol pour l'aménagement du Parc National de Mozogo-Gokoro (PNMG), situé en zone sahélo-soudanienne, région de l'Extrême-Nord au Cameroun. Les données obtenues décrivent un sol favorable à la production végétale : texture sablo-limoneuse, activités biologiques présentes et absence d'érosion. La végétation présente une physionomie de forêt sèche claire à dense. La diversité compositionnelle montre sa grande richesse floristique, avec 62 espèces de ligneux identifiées. L'indice de Shannon est évalué à 3,75 bits avec une équitabilité de 0,84. Dans sa structure, il peut être relevé une densité très élevée (2972 tiges/hectare) et la forte représentativité des moyennes et hautes tiges, preuves de sa grande préservation. Les types phytogéographiques rapprochent la végétation des zones soudaniennes à guinéennes. Ces caractéristiques peuvent lui conférer le statut d'écosystème de référence montrant un transfert d'espèces des zones guinéennes et soudaniennes au sahélien, malgré les menaces anthropiques notées. Ces spécificités floristiques peuvent s'expliquer par les mesures de conservation appliquées, la pédologie et la topographie (bas-fond, piémont). L'obtention d'attributs vitaux, de façon plus approfondie, pourrait confirmer ces analyses et contribuer plus significativement à son processus d'aménagement.

This study assesses land cover change of the Koupa Matapit forest gallery, West Cameroon, in relation to anthropogenic factors. Ethnobotanical surveys were conducted to investigate the relationships between the local population and the gallery forest; the spatio-temporal dynamics of the landscapes around the gallery forest were studied from the diachronic analysis of three Landsat TM satellite images of 1984, Landsat ETM + 1999 and Landsat OLI_TIRS of 2016, supplemented by verification missions on field. The satellite images were processed using ArcGIS and Erdas Imagine software. According to surveys, it should be noted that agriculture and livestock are the main economic activities of the population of Koupa Matapit, agriculture and fuel wood collection for energy were the main anthropogenic activities responsible for deforestation and degradation of the forest gallery. The collection of non-timber forest products (NTFPs) would have a significant implication in land use and cover changes. The results indicate that the extension of savannah/agricultural land (from 6989 ha in 1984 to 7604 ha in 2016) and bare soil/built up area (from 71 ha in 1984 to 342 ha in 2016) would have led to the disappearance of much of the forest area (1465 ha in 1984 to 580 ha in 2016). The rapid population growth of Koupa Matapit would be responsible for these pressures. There is an urgent need to implement appropriate land use policy in this area.

Gum arabic production from Acacia senegal is lower in sub-humid areas than arid areas. Water stress is thought to be the reason for higher yields in arid areas. The application of ethephon is thought to mimic the effect of water stress in other plants. The objective of this study was to determine if the application of ethephon would increase the gum yields of Acacia senegal under sub-humid conditions in Cameroon. Trees receiving 40 or 120 mg ethephon were compared to controls in field experiments at a semi-arid and a sub-humid location in Northern Cameroon, over two seasons. Two provenances from drier areas (Sudan) were compared to the local one. In the first season, gum yield of the local provenance treated with ethephon was increased by 400-600 % compared to the untreated trees. Gum yield at the semi-arid location was 77, 313 and 214 g/tree with 0, 40 and 120 mg ethephon/tree, respectively, while at the sub-humid location, it was 30, 186 and 114 g/tree with 0, 40 and 120 mg ethephon/tree. However, in the second season, the effect of ethephon was not significant in the semi-arid area, whereas it was evident in the sub-humid area (up to 478 g/tree). Moreover, ethephon did not affect gum yield of provenances from drier areas (Sudan). This showed that the water-stress hypothesis has to be refined. The development of ethephon-based tapping systems is promising, but requires further studies with a wider range of environmental conditions and A. senegal provenances.

No abstract

Ochratoxin A (OTA) is a mycotoxin that contaminates several foodstuffs, including cocoa. It has nephrotoxic, teratogenic and carcinogenic properties in humans. The effect of post-harvest processing and storage on the OTA contamination of cocoa was studied over three successive cocoa seasons (2005, 2006 and 2007) in Cameroon. The type of fermentation (box or heap) did not significantly influence bean OTA content, which varied from undetectable (<0.03 ng/g) to 0.25 ng/g, remaining below 2 ng/g (the defined standard for cocoa beans). However, pod damage and late pod opening were aggravating factors for OTA contamination of cocoa. If pods were not intact (intentionally or naturally damaged), OTA was found in samples with contents of up to 75.5 ng/g before processing and 32.2 ng/g after 4 months' storage. This contamination exceeded the levels tolerated for export. In addition, some of the cocoa produced is processed locally and consumed as chocolate, cocoa powder, chocolate filled sweets, cocoa-based drinks and cocoa butter. In Cameroon, the average daily consumption of cocoa by-products is estimated at 0.75 g/d for adults and 1 g/d for children. Consequently, for maximum OTA contamination of cocoa beans, the maximum daily exposure to OTA would be 1.61 ng/kg bw/d in young children weighing around 20 kg, greatly contributing to the exposure of young consumers.