The impact of invasive species on social-ecological systems: Relating supply and use of selected provisioning ecosystem services

Understanding the sustainability of social-ecological systems requires quantifying the relationships between ecosystem service supply and use. However, these relationships, and the influence of environmental change on supply and use, are poorly known. Here we apply a nested sampling design to analyse supply-use relationships in ten administrative units in each of two Eastern African regions undergoing invasion by an alien tree, Prosopis juliflora. Ecological data on supply of two key provisioning services, woody and herbaceous biomass, were collected in field plots and the use, defined here as income and livestock numbers, was assessed using household surveys. Supply and use were then up-scaled to the level of the smallest administrative unit. High Prosopis cover affected the supply of both services, with increased woody biomass but reduced herbaceous biomass. We found that supply of woody biomass was positively associated with income from wood sales. Prosopis invasion reduced income from livestock and slightly decreased cattle numbers over the past ten years. We propose that biophysical and socio-economic data collected at the same scale can help to determine supply-use relationships for ecosystem services and we discuss how integration of supply-use data can inform sustainable management of social-ecological systems in the context of environmental change.