How to assess realized ecosystem services: Indicators, challenges in determining actual use, and suggestions

Ecosystem services (ESs) are the benefits that humans receive from ecosystem functions, processes, or characteristics. In practice, many assessments do not distinguish between realized ESs—actually used or received by humans—and ecosystems’ capacities to provide services. These capacities can be referred to as potential ESs. The realization of ESs requires not only these ecological capacities but also human perception, use, or the fulfillment of human demand. Therefore, assessing realized ESs is more complex than assessing potential ESs. This study synthesizes 66 indicators for assessing 34 types of realized ESs and highlights a subset of indicators potentially applicable to environmental-economic accounting. It also explores the challenges in determining people’s actual use of ESs, such as identifying which areas benefit from ESs, determining whether ESs are actually used, and deciding who should assess the fulfillment of human demand for ESs. These challenges arise from (1) the intangible and public nature of certain ESs, (2) the distance decay that ESs may exhibit, (3) the long-term and broad societal need for ESs, (4) the fact that some ESs may be received remotely from multiple directions without active or direct human intervention, and (5) the potential human-induced pressures that the realization of ESs may place on ecosystems. The management and assessment of realized ESs should be guided by experts, while also incorporating public perspectives and disclosing the limitations and assumptions of the assessment methods. Furthermore, the realization of ESs must remain within the ecosystems’ capacities to provide them sustainably, and these capacities should be protected. There should also be mechanisms through which the potential supply of ESs can be delivered to humans. This study aims to support ES researchers, managers, and decision-makers in evaluating realized ESs, thereby tracking and managing the actual contributions of ESs to socio-economic development and human well-being.