Groupements floristiques et capacité de régénération des espèces ligneuses des sanctuaires boisés dans l’aire culturelle bwaba (département de Bondoukuy, Ouest Burkinabé) | Floristic communities and regeneration capacity of woody species of the wooded shrines of the Bwaba cultural area (department of Bondoukuy, Western Burkina Faso)

Wooded shrines are often considered in various regions of the world as places of biodiversity conservation and as relics of primeval nature, although some authors have shown the anthropised character of their flora. It has also been shown that the attached protection linked to the religious character cannot be systematically equated with the biodiversity conservation. However, in Sudanian regions, the forest physiognomy of the wooded shrines generally deeply contrasts with the surrounding savannah vegetation. Therefore, the vulnerability of these groves and their importance as reservoirs of plant biodiversity deserve to be evaluated. The present study aims to characterize the vegetation of wooded shrines in the Bwaba cultural area in Western Burkina Faso, in terms of forest resources and of phytodiversity conservation. It is based on an exhaustive inventory of wooded shrines of the Bondoukuy department. These were identified through interviews held with the traditional custodians of sacred sites in each of the 20 villages of the department. The wooded shrines were located, outlined with a GPS and mapped. Then, their distance to village and their surface were calculated. An area of 1600 m² was considered as the minimum area for the phytosociological relevés; groves of lower surface area were entirely inventoried. The abundance of trees and shrubs, as well as of their regeneration, was appraised with a numerical abundance index. The phytosociological communities were determined using a cluster analysis (Ward method); they were characterized by diagnostic species, assessed with the INDVAL index and by constant and dominant species. Three communities and five sub-groups were described: (1) the Diospyros mespiliformis–Anogeissus leiocarpa community, with three sub-groups (1_1) Terminalia laxiflora sub-group, (1_2) Guiera senegalensis sub-group, (1_3) Ziziphus mucronata–Anogeissus leiocarpa sub-group; (2) the Detarium microcarpum–Burkea africana community, (3) the Azadirachta indica community with two sub-groups (3_1) Azadirachta indica–Ziziphus mauritiana sub-group and (3_2) Diospyros mespiliformis–Azadirachta indica sub-group. Sudanian and Sudano-Zambezian species were dominant in all the communities; however, generalist species are more numerous in the communities where Azadirachta indica is dominant. Conversely, Guinean and Guineo-Congolian species, some of them being infrequent in the studied region, are more abundant in the groves of gallery forests (Ziziphus mucronata–Anogeissus leiocarpa community). Most (71%) of the wooded shrines are located near or inside villages; in addition, most of them are less than 1 ha in extent, some of them (16%) being smaller than the minimum area (0.16 ha). The local species richness (diversity) and the total richness (diversity, for which confidence intervals were computed for the sample-based rarefaction curves) are lower in small (< 0.16 ha) groves and in communities dominated by Azadirachta indica. Moreover, woody species regeneration is very low in groves dominated by Azadirachta indica. However, in all communities, the density of regeneration of the species seems related to their dominance in the observed vegetation. In conclusion, the flora of the studied wooded shrines is representative of the Anogeissus leiocarpa–Diospyros mespiliformis Sudanian dry forest and is significantly different from the pyrophilous flora of the neighbouring savannas. These wooded shrines therefore appear as places of conservation of species sensitive to fire; some of them (Anogeissus leiocarpa, Daniellia oliveri, Diospyros mespiliformis and Khaya senegalensis) are useful species that can be valuable for the reforestation of lands free from fires. These wooded shrines play a key role for the conservation of the main species of the dry forest, but their flora is threatened by anthropization, by the fragmentation of vegetation and by their sensitivity to invasive species.