The purpose of this paper is to test whether the monetary valuation of environment's elements is sufficient to define a sustainable management of the natural resources. This discussion rests on the one-year field experienec I realised in East-Cameroun in order to give an economic value to several elements of the forest ecosystem. But, beyond the attemps to valuate the local uses of the forest resources, our prospect was also to question the validity of money as a means of revealing the preferences of the villages towards the goods they exchange and the natural resources they use. For this, we analysed the place of the money in those local economies. Two aspects are considered : the part of the money within the villagers exchanges, and the study of the notion of richness (extrait résumé d'auteur)