The impact of roads on sub-Saharan African ecosystems: a systematic review

New major road infrastructure projects are planned or underway across sub-Saharan Africa (SSA) and are expected to have complex, and often deleterious, impacts on natural ecosystems across the region. For this reason, it is necessary to review evidence of how and through which mechanisms, roads might affect these landscapes. We reviewed 137 peer reviewed articles and documented 271 reported effects of roads and their underlying mechanisms inside and outside protected areas across SSA. Our findings show that (a) the study of the effects of roads on ecosystems in SSA is growing and not limited to the field of road ecology; (b) the negative effects of roads on species were reported at a similar frequency within and outside of protected areas; (c) the road-effect zone varied with effect but typically is between 1 and 7 km for larger mammals; (d) access to surrounding ecosystems through roads was the main mechanism driving effects; studies found accessibility influenced land use patterns and illegal hunting and harvesting; (e) other mechanisms by which roads affect (animal) species include, through functioning as a foraging site, and a habitat, and by acting as barriers to and corridors for movement; and (f) there was far more evidence on how roads can negatively impact ecosystems; in contrast, there was less certainty around mechanisms by which roads had no significant or a positive impact, since many of these were either speculated or unknown. An understanding of the underlying mechanisms can assist researchers and environmental assessment practitioners to predict how and where future road development might drive changes in biodiversity and land cover. Moving forward, we suggest that future research build a better understanding of the cumulative effects on different mammal and non-mammal communities and ecosystems more broadly and examine the socioeconomic contexts that characterize different road impacts in SSA.