In the context of Kyoto Protocol, forests can be used to create carbon credits. Contrary to the energetic sector where emissions reductions are considered as definitive, managing forests to mitigate climate change has been crticised because of the risks of reversibility. Biological carbon sinks are said to be non permanent. So, how can we compare carbon emissions reductions to carbon sequestration by sinks? What is the value of the carbon credits issued from forestry? In this study, we consider the debate surrounding carbon credits attribution. As a first step, we recall methods that have been suggested. Results of a case study dealing with a forest located in southwestern France are presented in the second part of the paper. In a final discussion, we wonder about financial impact of different geopolitical strategies.