Payments for ecosystem services (PES) have emerged as a tool to incentivize ecologically sound land management across sectors. In this study, we examine agroforestry systems as a promising option for smallholder farmers to enhance ecosystem service (ES) provision and conserve biodiversity. Agroforestry-related PES programs are emerging at global, regional and local scales, but programs for individual ES (e.g., carbon trading) may fail to support the adoption of diversified farming systems that would better provide multiple ES, enhanced biodiversity and long-term resilience. To enable PES programs that consider a bundle of ES, there is a need for methods to measure multiple ES, while understanding tradeoffs and synergies that may exist between them. We sought to develop comparable indices for nine ES related to water, productivity, biomass cycling and biodiversity under the ‘slash and mulch’ agroforestry system (SMAS) – an agroforestry alternative to the conventional maize-bean farming system currently practiced by some 11 million smallholders across Central America. We compared two variations of SMAS to conventional and organic management and forest-fallows in El Salvador using composite ES indices developed from 28 indicators collected in on-farm trials. Our primary objectives were to (1) assess management impacts on ES provision, (2) explore synergies and tradeoffs among ES and (3) examine the utility of simple field proxies for multiple ES.
Compared to conventional management, SMAS approximately doubled alpha biodiversity of woody vegetation and increased biomass inputs (i.e. soil mulch cover) by 34 – 57%. The agroforestry systems also improved water regulation and demonstrated lower incidence of erosion, pests, diseases and weeds; however, the high heterogeneity associated with the SMAS made it difficult to statistically demonstrate the benefits of individual ES indicators. By combining indicators into indices and evaluating all ES together, we were able to identify patterns showing that SMAS enhances multiple ES and better capitalizes on synergies between regulating and provisioning ES compared to conventional management. Specifically, SMAS treatments highlighted synergies between water regulation, pest and disease control, soil composition, belowground biodiversity and production value. In contrast, conventional plots showed tradeoffs between production value and other ES. Finally, we identified simple, easily measured field proxies that correlate well with multiple ES, and discuss important management, monitoring and policy implications for adaptable agroforestry systems.