1. Introduction
In the course of the past 10 years the importance of considering biodiversity and ecosystem services in environmental practice and policy assessment has gained considerable attention (MEA, 2005 and TEEB, 2010). A trend can be observed among policy-makers and various stakeholders to assess the monetary value of these environmental public goods in order to facilitate their recognition in decision-making. For example, in its Biodiversity Strategy the EU has set itself the target to map ecosystems and their services, as well as to assess their economic value for inclusion in national accounting systems by 2020 (European Commission, 2013).