Perennial species diversity, ecosystem carbon stocks and carbon income in coffee-based agroforestry systems along an elevation gradient in South-eastern Ethiopia

In the current context of deforestation, coffee-based agroforestry system (CAFS) is credited for climate change (CC) mitigation and biodiversity conservation while supporting local livelihoods. Despite integrating shade tree species in CAFS, empirical studies to support this assertion are inadequate in Eastern Africa, and hence, its ecosystem services provisions are less understood. We evaluated perennial species diversity, carbon (C) stocks in the biomass and soil organic C (SOC) along an elevation gradient of 72 plots of shade coffee, while 36 plots were selected for without-shade coffee systems within three elevations, namely, low (1600–1750 masl), mid (1750–1850 masl) and high (1850–2000 masl) elevations in Southeastern Ethiopia. The perennial species diversity and biomass, SOC, fine root and litter C stocks were evaluated. Perennial species Shannon diversity significantly differed among the studied elevations (p < 0.001). Shaded coffee had significantly higher ecosystem C stocks than without shaded coffee systems (p < 0.05). The highest C stocks were found in the soil in both coffee systems. However, we found a weak relationship between the Shannon diversity and biomass C. The C income in shaded coffee was 70 % higher than without shaded coffee systems. The present study showed that shaded coffee accumulates more C and provides additional benefits from C credits. Hence, CAFS deliver ecosystem services that enhance biodiversity conservation and CC mitigation while generating an additional C income for farmers. However, we learned that the impact of perennial plant diversity on C stock and C income is context and site-specific.