Stakeholder priorities determine the impact of an alien tree invasion on ecosystem multifunctionality.
While the ecological impact of environmental change drivers, such as alien plant invasions, is relatively well described, quantitative social-ecological studies detailing how these changes impact multiple ecosystem services, and subsequently stakeholders, are lacking. We used a social-ecological approach to assess how Prosopis juliflora (Prosopis henceforth), an invasive tree, affects the provision of multiple ecosystem services to different stakeholder groups in a degraded East African dryland. We combined plot-based ecological data on the impacts of the tree on indicators of ecosystem service supply with questionnaire survey data describing ecosystem service priorities from eight different stakeholder groups. These data were then used to quantify how tree invasion impacted individual ecosystem services, and the overall supply of services, relative to the priorities of each stakeholder group, using an ecosystem service multifunctionality metric. In the study area, we found that Prosopis significantly increased the supply of shade, wood production and honey production, but reduced the supply of water availability, tourism potential and biodiversity protection. Priorities for specific services differed between stakeholder groups. Although most groups assigned a high priority to provisioning services, such as water and crop production, it was either provisioning or cultural services which were a primary source of income, that were deemed most important. Combining supply and priority data showed that most stakeholder groups saw a net decrease in ecosystem service multifunctionality with increasing Prosopis invasion, or no significant change overall. Increasing Prosopis cover increased multifunctionality for only two stakeholder groups, charcoal producers and NGOs involved in regional development. Our research highlights the need to account for stakeholder priorities in studies of how global change impacts ecosystem multifunctionality. We found that there are conflicting patterns of ecosystem service priority between different stakeholder groups, resulting in large variation in how different groups were impacted by the invasive tree. Our approach also highlights possible synergies and conflicts when managing this tree invasion. More broadly, we recommend that future studies of ecosystem multifunctionality explicitly consider differing stakeholder priorities, as these strongly influence the perceived impact of environmental and land management change.