Floristic and structural diversity of woody vegetation in the Sudano-guinean zone of Larmanaye, Chad

Abstract

This study was carried out in the Larmanaye ecological landscape in the Sudano-guinean zone of Chad. The objective was to analyse the floristic and structural diversity of different woody-vegetation types. Floristic and dendrometric data were collected in 92 plots of 2500 m² to assess woody species with diameter greater than 5 cm, and 460 plots of 25 m² for the assessment of regeneration. The composition, diversity, diameter and height structure, density, species and family importance value of the woody species were described, evaluated and compared among vegetation types. A total of 80 species belonging to 63 genera and 25 families were recorded with 64, 61, 52 and 46 species respectively in tree-based savannah, gallery forest, croplands, and shrubby savannah. The families of Fabaceae and Combretaceae were the richest and abundant in the all woody-vegetation types. Shannon diversity index varied from 3.23 in the gallery forest to 2.72 in the tree-based savannah whereas the Pielou evenness index varied from 0.95 in the tree-based savannah to 0.91 in croplands. The distribution of stems of the main species in classes of diameter and height showed an “L” shaped curve. Mean density varied from 24.70 stems/ha in the tree based savannah to 9.65 stems/ha in the shrubby savannah. The levels of regeneration were low with seedlings proportion of 18.75, 15.83, 10.05 and 9.18%, respectively in croplands, tree-based savannah, gallery forest and shrubby savannah. Protection systems and appropriate management were therefore recommended in order to ensure the sustainability of the forest resources in Larmanaye ecological landscape. Key words: Floristic diversity, Larmanaye-Chad, regeneration, structure, woody vegetation type.