Ecosystem valuation is the pricing or assessment of economic capital asset value to a living ecosystem.
Value of services
The simplest form of ecosystem valuation is to hold that an ecosystem has a value equivalent to its ecological yield valued as it would be on commodity markets: for the value of water, wood, fish or game, that is purified or nurseried or generated or harboured in that ecosystem. Thus, a price can be put on the natural capital of an ecosystem based on the price of natural resources it yields each year. The Global Resource Bank is a project that seeks to replace national currencies with a single global currency based strictly on this capital yield - it is one of three global currency projects actively investigated by the UN.
More complex arguments in ecosystem valuation regard nature's services and the assignment of values in a service economy to all that nature does "for humans". Studies compiled by Robert Costanza in the 1990s argued strongly that even just considering the most basic seventeen of these services on which primary industry (agriculture) were worth more (US$33T) each year than the whole human exchange economy (US$25T) at that time (1995).
In Natural Capitalism, 1999, Paul Hawken, Amory Lovins and Hunter Lovins advanced an argument to assign the value of Earth in current currency. See value of Earth article for that and other examples of this extreme case of ecosystem valuation - biosphere valuation.
Is valuation economics, or ecology?
Such valuation, and that of the effectiveness of various environmental health measures that affect the value of life and quality of life, are usually thought to be part of economics. Natural capital and individual capital are studied ecology as living systems, however, this does not extend to the economics of valuation by which they are related:
Considering "valuation" as an "economic not ecological issue" reflects the way these fields divide of the activities of humans versus non-humans in "making a living". When humans go out to get food or homes, that is studied in "economics", but when non-humans do it, that is "ecology", though it is clear that there are motivations, methods and certainly bodily needs in common.
Since animals do not put explicit prices on ecosystems they use, but do behave as if they are valuable, e.g. by defending turf or access to water, it is mostly a matter of definition whether ecology should include valuation as an issue. It may be anthropocentric to do so, since "valuation" more clearly refers to a human perception rather than being an "objective" attribute of the system perceived. Ecology itself is also human perception, and such related concepts as a food chain are constructed by humans to help them understand ecosystems. In many cases
By those who hold that markets and pricing exist independently of any individual human observers and "users", and especially those who deem markets to be "out of control", ecosystem valuation is considered a (marginal, ignored) part of economics.
Some versions of conflict theory focus on the role of resource scarcity in sparking or propagating human conflicts - in effect holding that the resources or ecosystems they fight over are being held so valuable that they are worth considerable risk of harm to control. This is at least a relative notion of value and value at risk applied to ecosystem.