Environmental governance is driven by social representations of natural resources and ecosystem conditions. Environmental knowledge is therefore a possible resource for stakeholders’ claims in favor of production or preservation policies. When produced for this purpose, environmental knowledge is a policy instrument. As such, it carries policy frames in favor of production or preservation. This article questions how the use of environmental indicators influences environmental policy. We trace back the history of forest and water regulation in France and we show that there is no one way relationship between the use of ecological indicators and preservation policies. In forests, ecosystem knowledge has rather supported forestry practices and is produced by production-oriented sectoral actors. In water, ecosystem knowledge empowered ecologists who opposed resource-centered productivist management.