eration was given to the wide range of interests in the results of the test, including the varied interests of the Indian tribes along the Grand Canyon, the process used in getting inputs from these interests was not clear in the reports on which this case study is based.
Biodiversity presents two kinds of challenges for valuation: complexity and preponderance of nonmarket benefits. Biodiversity is an especially complex good, service, or amenity; in some ways, it is all these things. It might be most appropriate to think of biodiversity as a state of the world. Biodiversity involves complex suites of environmental services and amenities, which raise difficulties of several kinds:
Although we should be mindful of the inherent complexity of biodiversity, not all valuation tasks call on us to address its full extent (see the Pacific Northwest case study, below). Often, we are asked to value not total biodiversity, but the benefits and costs of proposed actions that would make relatively modest changes in it, for example, actions addressing just a few species in a particular place or modifying a particular section of habitat. The challenge of valuing modest changes in biodiversity is not trivial, but the task is more manageable than valuing total biodiversity. We note that, according to Norton (1988), a long series of marginal decisions can collectively make nonmarginal changes; and WTP to prevent those nonmarginal changes is greater than the sum of the mar-