Assessing urban open space network connectivity in semi arid Windhoek, Namibia

Abstract

With more than half of the world's population living in urban areas, and urbanisation increasing rapidly in sub-Saharan Africa, there is constant pressure on cities to accommodate people. Urbanisation is one of the main factors driving biodiversity loss in urban centres as it can lead to fragmentation and ultimately degradation or loss of natural areas. These natural areas are part of a city's green infrastructure, responsible for providing valuable ecosystem functions and services. As one of the key principles of urban green infrastructure planning, natural areas in cities should be functionally connected in order to effectively contribute to ecosystem functioning and support a healthy biodiversity. Efforts to preserve or restore ecological connectivity in urban areas can be costly, especially in a semi-arid, Global South city such as Windhoek in Namibia. Properly informing attempts to assess functional connectivity in the highly heterogeneous landscape of a city requires the use of reliable, efficient, and process-driven models and metrics to map movement corridors, and not merely the shortest routes, between habitat patches. This study tested the use of electrical circuit theory modelling, as applied to ecological concepts, to map multiple movement corridors between open space parcels in Windhoek, based on a resistance-to-movement cost surface and incorporating maximum dispersal distances of small to medium sized mammals to quantify functional connections. Focussing on threatened linkages which play a critical role in keeping the network connected would ensure a more cost-effective use of available resources. Promising results included mapped least cost corridors and paths, mapped current flows showing pinch points to dispersal movement, and weighted measures of patches' importance for keeping the entire network connected. Also, based on the parameterization used, a single linkage in a highly resistant area was found to be the only connection between large components of Windhoek's open space network. Based on interpretations of the mapped outputs, inter-patch areas displaying improvement potential to serve as possible linkages between isolated components were also identified. As a test for improvement potential, in one of these inter-patch areas a vacant lot was "upgraded" to habitat status and the resulting re-run showed clear, run-on improvements to patch importance in that area. Consequently, the circuit theory modelling approach shows promising potential for assessing functional connectivity at city-scale in a semi-arid, sub-Saharan urban setting. Applying this approach in urban areas, specifically those with resource constraints, can greatly enhance urban nature conservation efforts and inform responsible spatial development planning decisions.