A comprehensive study of erosivity and soil erosion over a small tropical islet: Round Island, Mauritius

Round Island, a small (219‐ha) volcanic island 22.5 km north of Mauritius, has steep slopes and thin soils. This small tropical island was previously subjected to overgrazing by goats and rabbits, which detrimentally affected ecosystem functioning. Classified as a nature reserve since 1957, Round Island houses the last remnant of palm savannah that has been lost on mainland Mauritius and is a refuge to several endemic and endangered species. Landscape restoration and ecosystem functioning on Round Island are key conservation objectives, but soil erosion remains a significant hindrance to habitat restoration and ecosystem functioning. Here, we investigate soil erosion on Round Island and assess the implications for conservation and management. Sediment movement was monitored monthly (2015–2018) at seven soil erosion plots coupled with rainfall and erosivity measurements. A mean annual sediment movement rate of 0.2136 t ha⁻¹ yr ⁻¹ is calculated. Although this rate of sediment movement is low for humid tropical regions, the barren landscape and low contemporary rates of soil erosion suggest that most of the erodible soil has already been eroded. Interrill erosion of the shallow soils and friable parent material is closely correlated with rainfall erosivity and exacerbated by limited vegetation cover. Continued revegetation is recommended to retard soil erosion and restore ecosystem functioning. The paper also emphasises that rainstorms are the greatest single phenomena affecting earth surface processes on and around the island of Mauritius. As such, long‐term monitoring of the interaction between the surface and climate is required to provide insights for conservation management.