3. Material and methods
Although facing severe conceptual issues, the valuation of biodiversity has become a widely developed area of research, and we have to come back to the methods and techniques that economists have build in attempts to circumvent these obstacles.
3.1. On the valuation techniques
During the last decades, a large scientific and administrative literature has repeatedly reviewed the available methods to produce practical measurements of ecosystem services values [38]. First, the ‘‘total economic value’’approach does not pretend at estimating an absolute value of ecosystems, but rather to allow adding the multiple economic reasons [5] that underlie the social values associated with ecosystems. The valuation and the comparison inherent in it must be built from observations.
What is observable? Ultimately, it is the individuals’preferences that must be made observable, which may involve helping individuals to build them.