The Ecology of Urbanization: The Case of Ouagadougou, Burkina Faso

Abstract

African urban population is expected to exceed 50% by 2030 (UN 2010). Understanding of processes, which dominate the ecology of urban areas is crucial for better management and urban planing particularly of developing cities in vulnerable environments. As many cities in the developing world, Ouagadougou, the capital of Burkina Faso has been increasing dramatically in population and in area, a process which is predicted to continue (UN 2010). Ouagadougou is located in the Sudan-Sahel, south of the Sahara, an area which suffered severe droughts in the 1970's and 1980's. This vulnerable environment and the on-going process of urban sprawl set the scene for the current investigation. The present research takes its point of departure in a remote sensing analysis of Normalized Difference Vegetation Index (NDVI), as a proxy for Net Primary Production (NPP), for the area of Ouagadougou for the years 2000 to 2009. This analysis indicate a spatio-temporal pattern of decreasing ecosystem productivity in patches organized as a wide belt around Ouagadougou, while areas at the centre of the city show no change or increasing productivity. The field investigation, integrating social and ecological methods, included semi-structured interviews, transect-walks, analysis of the plant community (canopy cover and functional structure) and availability of soil nutrients (C, N, P) at different patches. The results reveal that anthropogenic activity is highly influential for the spatial distribution of phosphor in the urban soils, and for the distribution and functional structure of urban vegetation. On the other hand, carbon and nitrogen distribution in the soil was found to be determined by water availability and positively related to vegetation. Yet, the results also indicate high variability inside the urban ecosystem, variability which is scale and context-dependent.