This study was carried out in the classified forest of Djoli-Kera found in the SouthEastern part of Chad. It aimed to analyze the spatial and temporal dynamics of land cover between 1972 and 2013 and to determine the drivers of vegetation degradation. The databases used were made up of 4 Landsat satellite images (1MSS of 1972, 5TM of 1984, 7ETM+ of 1990 and 2010) and a spot 6 image of 2013, supplemented by field studies. Satellite images were processed using ENVI and ArcGIS software. Interview was used to identify the activities carried out by the local population. In 1972, the classified forest consisted of four types of land cover, the most important of which was open forest (51%), followed by wooded savannah (26%), tree savannah (21%) and sparse vegetation consisting of farms and fallows (2%). Gradually open forest and tree savannah disappeared. In 2013, the main types of land cover were shrub savannah (40%), sparse vegetation (28%), wooded savannah (12%), bare soil (12%) and dwellings (8%). Livestock, agriculture, wood collection and bushfires are perceived by local population as main drivers of forest cover change. Awareness-raising, monitoring and regulation of access to resources must be pursued, but also managers of the classified forest must accompany the local populations in the planting of trees and the setting up of more efficient farming systems to reduce pressure on the forest's resources.
REMERCIEMENTS Ce travail a été réalisé grâce à l'appui financier de l'Agence Panafricaine de la Grande Muraille Verte et de l'Agence Nationale de la Grande Muraille du Tchad. RESUMELa connaissance des caractéristiques du peuplement ligneux du tracé de la Grande Muraille Verte (GMV) du Tchad permet de comprendre leur structure et fonctionnement afin de proposer des stratégies de gestion durable. C'est dans ce cadre que ce travail vise à caractériser la flore et la végétation ligneuses sur le tracé de la GMV du Tchad. La méthodologie utilisée consiste à déterminer la composition floristique et la structure du peuplement ligneux dans les trois sites retenus (Lac, Kanem et Bahr El Ghazal) Characterization of the ligneous populatings on the route of the Great Green Wall in Chad ABSTRACTThe knowledge of ligneous populating characteristics of the route of the Great Green Wall (GGW) of Chad helps to understand their structure and function in order to propose strategies for sustainable management. This study was carried out to characterize the flora and the tree vegetation present on the Chad M. MAHAMAT-SALEH et al. / Int. J. Biol. Chem. Sci. 9(5): 2617-2627, 2015 2618 Great Green Wall (GGW) line. The methodology consisted in determining the floristic composition and the structure of the tree population in three sites: Lac, Kanem, and Bahr El Ghazal. The floristic inventories have identified 18 species distributed into 15 genera and 9 families. Trees are dominated by the Mimosaseae family. The distribution by classes of height and circumference of the trees indicates a predominance of the shrub layer in all the three sites. The study of the natural regeneration reveals that Acacia raddiana and Balanites aegyptiaca present the highest regeneration potential in the three sites. Globally, the results obtained in this study show that the most adapted species to the ecological conditions of the Chad's GGW are Acacia raddiana and Balanites aegyptiaca. Consequently, these species must be considered during the restoration of the given ecosystems.
1 RÉSUMÉ La présente étude a pour but d’étude la dynamique des peuplements ligneux dans le Parc National de Manda. Elle vise à déterminer les caractéristiques structurales, la composition spécifique et la régénération des peuplements ligneux. Quatre sites ont été implantés depuis 2012. Nous avons procédé à la caractérisation des peuplements ligneux par des relevés dendrométriques. La flore ligneuse dans l’ensemble des sites est riche de 87 espèces reparties en 56 genres et 22 familles. Les sites 1 et 2 ont des effectifs plus élevés en 2019 comparativement en 2014 et en 2012. Une forte régénération s’est effectuée durant l’année 2019. Contrairement aux sites, 1 et 2, les sites 3 et 4 présentent pour l’année 2019 une forte baisse des effectifs de jeunes plants. Ces jeunes plants sont très sensibles non seulement à la disponibilité des ressources en eau pour franchir la saison sèche mais aussi à l’intensité et à la fréquence de passage des feux. Les résultats ont permis de noter que la densité moyenne entre 2012 et 2014 s’est accrue et à partir de 2014 elle s’est stabilisée. La surface terrière par hectare est, en moyenne de 10,12 m2/ha pour 2012 ; 11,16 m2/ha pour l’année 2014 et de 11, 65 m2/ha pour l’année 2019. Pour l’ensemble des sites expérimentaux, on évalue le volume moyen de bois sur pieds à 12,31 m3/ha en 2012, à 12,46 m3/ha en 2014 et 12,08 m3/ha en 2019. Ces valeurs indiquent que les variations de volume moyen de bois sur pieds sont très faibles pour les sites pris dans leur ensemble. Les résultats obtenus, montrent aussi que 8 espèces se situent dans un processus d’évolution régressive et 4 autres dans un processus d’évolution progressive. La structure des peuplements ligneux n’a pas beaucoup évolué en 8 ans mais, elle apparaît fortement tributaire de la topographie et de la pression anthropique. ABSTRACT Dynamic of the woody populations in the National Park of Manda, to the south of Chad The purpose of this study is to study the dynamics of woody stands in the Manda National Park. It aims to determine the structure, specific composition and regeneration of woody stands. Four sites have been established since 2012. We have characterized the woody stands by dendrometric surveys. The woody flora in all sites is rich in 87 species divided into 56 genera and 22 families. Sites 1 and 2 have higher numbers in 2019 compared to 2014 and 2012. Strong regeneration took place in 2019. Unlike sites 1 and 2, sites 3 and 4 present for the year 2019 a sharp decline in the number of young plants; these seedlings are very sensitive not only to the availability of water resources to cross the dry season but also to the intensity and frequency of fire. The results showed that the average density between 2012 and 2014 increased and from 2014 it stabilized. The basal area per hectare is, on average, 10.12 m2 / ha for 2012; 11.16 m2 / ha for the year 2014 and 11, 65 m2 / ha for the year 2019. For all the experimental sites, the average volume of standing timber is estimated at 12.31 m3/ ha in 2012, 12.46 m3 / ha in 2014 and 12.08 m3 / ha in 2019. These values indicate that variations in average volume of standing timber are very low for sites taken as a whole. The results obtained also show that 8 species are in a process of regressive evolution and 10 in a process of gradual evolution. The structure of woody stands has not changed much in 8 years, but it appears highly dependent on topography and anthropogenic pressure.
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