Management and protection of large old tree species in farmlands: Case of Milicia excelsa in southern Benin (West Africa)

Abstract

Agroforestry systems are the last refuge habitats for many large old trees. This study assessed the management and the protection of Milicia excelsa (Iroko) trees in agricultural landscape of Dogbo district in southern Benin. A socio-economic survey with 288 respondents combined with an inventory of M. excelsa trees in agricultural lands were carried out. A total of 404 Iroko's trees were geolocated in 10 stands ranging in size from 102 to 1476 ha. The pair correlation function has been used to assess the spatial patterns of Iroko trees. The density of Iroko trees varies moderately from 1.69 ± 0.19 to 0.07 ± 0.02 stems/ha respectively in farmland and landscape with a spatial distribution ranging from gregarious to random - gregarious - random. The diametric structure of Iroko trees presents a bell-shaped appearance with a left asymmetry. The vertical structure shows a bell-like appearance centered on the modal class made up of individuals of height between 14 and 16 m. Timber exploitation (14%), rarefaction of the species and its attribute of sacred tree (98%) are the main motivations for protecting plants in agricultural lands. The medicinal use of the plant parts of Iroko is mainly based on the bark (33%) and leaves (24%). Except the socioeconomic conditions of farmers, the cultural foundations contribute the most to the preservation of M. excelsa in the agricultural lands. Thus, a participatory reforestation program integrating the endogenous values of local populations in the use of agroforestry systems as biological corridors could be successfully implemented. It would allow the preservation of large old trees from the increasing pressure on their populations in the future.