Ecosystem services are the direct and indirect contributions of ecosystems to human well-being1. The benefits they deliver are valuable to humans and it is the quantification of these values that is the subject of environmental valuation. In economic terms, value can be expressed through exchange and it is usually assessed employing the concept of willingness to pay (WTP). Environmental valuation quantifies how much of an individual’s existing wealth s/he is willing to trade for an increase in the provision of a certain ecosystem benefit. The WTP amount can be interpreted as an indicator of the change in well-being that this individual expects from the increased ecosystem benefit provision. In certain circumstances this WTP amount can be aggregated over all individuals in an economy.
If the benefits provided by ecosystem services are directly traded in markets (e.g. fish landings) or contribute to the production of marketable goods or services (e.g. water purification supporting fisheries), market data itself can be used to value ecosystem benefits. When ecosystem benefits are not traded through markets, other techniques to determine the WTP for their provision, and therefore their value, have to be employed. So-called stated preference methods use surveys to assess what people are willing to pay for improved environmental quality or ecosystem benefits. In such surveys a hypothetical market is constructed and respondents are asked to indicate how they would behave in this market. In the case of the Contingent Valuation Method (CVM), respondents directly state their maximum WTP for a specified change in the provision of an ecosystem benefit. In Discrete Choice Experiments (DCE) respondents indicate their preferred alternatives out of a set of policies that lead to different changes in ecosystem benefit provision at different costs.
In recent years, criticism against monetary valuation has led to the development of so-called deliberative valuation methods. Deliberative valuation still strives to assess environmental values but, in some cases, refrains from using money as the measuring unit. These methods involve participatory techniques, such as workshops or focus groups, and provide participants with information about the ecosystem benefits of interest and their use and management. Participants are invited to question and deliberate over the information before coming to a more informed conclusion about their individual, or in some cases, group values.