Proximity to high densities of pastoral settlements reduces grassland regrowth in a protected tropical savanna

Abstract

AbstractSedentarization of pastoralist communities is reshaping the structure and functioning of tropical savannas. Of particular concern is how permanent pastoral settlements change grassland vegetation inside “protected” areas. In this study, we investigate the spatial impact of pastoral settlements on grassland regrowth in Nech Sar National Park, Ethiopia. Within the National Park, we established herbivore exclosures across the central grassland plains at varying distances from a high concentration of pastoral settlements. Plant species composition, biomass, and regrowth after clipping were measured every 6 months, inside and outside exclosures in close proximity and further away from pastoral settlements. After 18 months, close proximity to high densities of pastoral settlements negatively influenced grassland regrowth compared to further away from pastoral settlements. Excluding herbivores resulted in lower regrowth compared to grazed swards independent of distance from high densities of pastoral settlements. Cover of the dominant grass species Bothriochloa insculpta was lower when grazed and following clipping, whereas Chrysopogon plumulosus cover was higher closer to settlements. These grasses were dominant across the plain; yet further away from settlements there was a higher number of co‐dominant grassland species. These findings suggest that subtle changes in grassland community composition, likely following livestock grazing, contribute to spatial differences in savanna grassland regrowth near to and far from pastoral settlements. Furthermore, specific grassland species may be used as indicators of the wider spatial impact of pastoral settlement sedentarization on savanna regrowth.