The 2020 Biodiversity Strategy was the first EU policy to highlight the “immense value of ecosystem services and the urgent need to maintain and restore these for the benefit of both nature and society” (1) and requires EU member states to map and assess their ecosystem services.

Ecosystem Services (ES) are defined as “the benefits humans obtain from ecosystems” - these can be direct (e.g. food, raw materials) or indirect (e.g. regulation of water supply and quality, nutrient cycling). As such, the ES concept has a strong anthropocentric focus and does not include biophysical structures and processes (e.g. vegetation cover, primary production) or functions (e.g. slow passage of water) that do not directly or indirectly contribute to human well-being.

In the past 15 years the ES concept has gained increasing interest in research, policy and decision making, and a wide range of ES approaches emerged. With the aim to provide a standardized classification of ES the “Common Classification of Ecosystem Services” (CICES) was developed. It includes three categories of ES, that is provisioning (e.g. firewood, food), regulating (e.g. climate regulation, water purification) and cultural services (e.g. recreation, scenic values) and describes them in a five-level hierarchical structure which consists of Sections (e.g. Provisioning), Divisions (e.g. Biomass), Group (e.g. Reared animals for nutrition, materials or energy), Classes (e.g. Animals reared by in-situ aquaculture for nutritional purposes) and Class types (e.g. Animals by amount, type) and covers both, biotic and abiotic ecosystem outputs. The hierarchical structure provides flexibility for ES assessments to address different spatial scales and levels of information (2).

ES assessment methods and tools can be broadly grouped into quantitative (data-based) and qualitative (expert-based) assessments. The choice of method or tool depends on the assessment purpose, required outputs and practical considerations such as time efforts, data availability and required expertise.

First quantitative ecosystem services assessments focused on monetary valuations. A study by Robert Constanza and others (1997) estimated that the global economic value of the ecosystem services is in a range between USD 16-55 trillion, of which 63% were considered to be contributed by coastal and marine ecosystems. Despite the high level of uncertainty, monetary valuations can be beneficial for including non-market values into cost-benefit analyses in order to better reflect the value of ecosystems or to show the socials costs of ecosystem loss. Furthermore, they can be used for compensation mechanisms in order to compensate e.g. landowners for good management practices that support conservation. Other quantitative methods make use of monitoring, modelling or spatially explicit data. Quantitative methods are for instance used to develop baselines to monitor changes over time or for evaluating implications of management decisions or policy changes. Qualitative assessments are often considered to be more subjective, but are practical for scoping and identifying relevant services and prioritising sites for in-depth research, identifying stakeholder groups that benefit from particular services, and to bring people together to think about ES values and management implications. (3)