Handling a messy world: Lessons learned when trying to make the ecosystem services concept operational

The concept of ecosystem services is widely used in the scientific literature and increasingly also in policy and practice. Nevertheless, operationalising the concept, i.e. putting it into practice, is still a challenge. We describe the approach of the EU-project OpenNESS (Operationalisation of Ecosystem Services and Natural Capital), which was created in response to this challenge to critically evaluate the concept when applied to real world problems at different scales and in different policy sectors. General requirements for operationalization, the relevance of conceptual frameworks and lessons learnt from 27 case study applications are synthesized in a set of guiding principles. We also briefly describe some integrative tools as developed in OpenNESS which support the implementation of the principles. The guiding principles are grouped under three major headlines: ". Defining the problem and opening up the problem space", ". Considering ethical issues" and ". Assessing alternative methods, tools and actions". Real world problems are often "wicked" problems, which at first are seldom clear-cut and well-defined, but often rather complex and subject to differing interpretations and interests. We take account of that complexity and emphasise that there is not one simple and straightforward way to approach real world problems involving ecosystem services. The principles and tools presented are meant to provide some guidance for tackling this complexity by means of a transdisciplinary methodology that facilitates the operationalisation of the ecosystem services concept.