Alien plant species dominate the vegetation in a city of Sub-Saharan Africa

Although many African cities are confronted to an important population growth, there are almost no studies describing their vegetation and how it is affected by the urbanization process. We present here the description of the spontaneous vegetation of the capital city of Burundi, Bujumbura, through the analysis of 437 vegetation plots. Ruderal plant assemblages dominate in the most urbanized areas while in the outskirts of the city, the vegetation shows similarities to natural plant assemblages in the region. The variability of the plant assemblages is further influenced by the degree of shade, the presence of a permanent source of humidity and trampling by humans and cattle. Over the 404 species recorded in the plots, 57% are native and 43% are introduced. Sixty percent of the 173 introduced species originate from tropical America. It is very likely that in the future, if no biodiversity conservation measures are taken, the urbanization process will lead to the homogenisation of the vegetation in favour of ruderal plant assemblages and introduced species. Similarly to what is done in temperate countries, urban planners in African cities should take measures to preserve the last patches of semi-natural vegetation, not only for their conservation value, but also for the diversity of services they offer to the population.

Research highlights
► Alien plant species dominate the vegetation of the city of Bujumbura (Sub-Saharan Africa). Most of these species originate from tropical America.
► The urbanization process leads to the homogenisation of the vegetation in favour of ruderal plant assemblages and introduced species.
► Urban planners in African cities should take measures to preserve the last patches of semi-natural vegetation and to reduce the expansion of invasive species.