Domestic garden plant diversity in Bujumbura, Burundi: Role of the socio-economical status of the neighborhood and alien species invasion risk

Domestic gardens can have both positive and negative effects on urban biodiversity conservation. We analyzed the flora of 1045 gardens in Bujumbura, Burundi. Among the 567 species identified in the gardens, 85% were not native. They originate mainly from tropical America (43%), tropical Asia (30%) or Africa (17%). Three plant assemblages were defined from a cluster analysis, corresponding to ornamental gardens, utilitarian gardens (plants used for fencing and food production), and mixed gardens (intermediate between the two former types). A Non-metric Multidimensional Scaling analysis showed that the main floristic gradients in the garden vegetation were correlated to the socio-economical status of the neighborhood. High standing neighborhoods have higher proportion of ornamental gardens while most gardens in the popular and semi-rural neighborhoods are utilitarian. The species richness per garden was highest in high standing neighborhoods, mainly due to an area effect. When controlling for garden area, species richness is highest in the middle class neighborhoods. City gardens play an important role in the functioning of the urban ecosystem and provide shelter to native plant species and to the urban fauna. However, gardens also are sources of introduction of alien species. In Bujumbura, 9% of the alien garden species have already naturalized in the city, among which 14 invasive species. This number is expected to increase in the coming decennia as there are about 121 other garden species that present a high invasion risk: they are invasive in other parts of the world in climates comparable to that of the Bujumbura region.

► Plant diversity patterns of urban domestic gardens correspond to a socio-economic gradient.
► Most plants in the domestic gardens in Bujumbura are alien species.
► Gardens are a source of potentially invasive species.