The value landscape in ecosystem services : value, value wherefore art thou value?

Ecosystem services has risen to become one of the preeminent global policy discourses framing the way we conceive and articulate environment–society relations, integral to the form and function of a number of far-reaching international policies such as the Aichi 2020 Biodiversity Targets and the recently adopted Sustainable Development Goals. Value; its pursuit, definition, quantification, monetization, multiplicity and uncertainty, both in terms of meaning and attribution, is fundamental to the economic foundations of ecosystem services and a core feature driving its inclusion across multiple policy domains such as environmental management and conservation. Distilling current knowledge and developments in this arena are thus highly prescient. In this article, we cast a critical eye over the evidence base and aim to provide a comprehensive synthesis of what values are, why they are important and the methodological approaches employed to elicit them (including their pros and cons and the arguments for and against). We also illustrate the current ecosystem service value landscape, highlight some of the fundamental challenges in discerning and applying values, and outline future research activities. In so doing, we further advance ecosystem valuation discourse, contribute to wider debates linking ecosystem services and sustainability and strengthen connections between ecosystem services and environmental policy.