Effect of urbanisation on woody vegetation: case of the Dakar region, Senegal

Abstract

Urbanisation is one of the main factors transforming ecosystems, with marked effects on floristic composition and society-nature relations. In the Dakar region, despite rapid urbanisation, interactions between urbanisation gradients, woody vegetation, and social perceptions remain poorly documented. This study analyses the effects of urbanisation on the structure, diversity, and origin of woody species, as well as on community motivations towards trees. The methodological approach is based on an urbanisation gradient comprising an urban area (Hann Bel Air), a peri-urban area (Mbao), and a rural area (Bambilor), combining floristic inventories and socio-economic surveys. A total of 3,363 individuals representing 128 species and 74 families were inventoried. The rural area has the highest species richness (53 species), abundance (2,053 individuals), and diversity (H’ = 4.53 bits), while the urban area has lower species richness (38 species) but relatively high evenness (E = 0.80). Woody plant density increases very significantly (P-value < 0.001) from urban to rural areas (69.56 ± 44.97; 52.62 ± 29.21 and 114.06 ± 48.13 individuals.ha-1, respectively), reflecting land availability and different land uses. The floristic composition varies significantly along the gradient, with a dominance of exotic species, notably Leucaena leucocephala in urban areas (2.74%), Anacardium occidentale in peri-urban areas (6.05%), and Mangifera indica in rural areas (10.62%). Surveys reveal that the motivation to plant trees decreases from urban to rural areas, where planting initiatives are mainly carried out by forestry services rather than local populations. These results highlight the need for differentiated tree cover management that integrates ecological dynamics and socio-economic dimensions to promote sustainable development strategies, tailored to each zone of the gradient.