Quantification of forest biomass is a challenge for developing countries due to insufficient data and lack of expertise. Involving villagers in this work, especially in the case of local forests could improve the speed and efficiency of this quantification process. This article describes the participatory approach implemented to assess carbon stocks in two community forests located in south-eastern Cameroon. This was put into practice for forest inventory work and the estimation of biomass and carbon stocks. The aim was to use classic scientific approaches of inventory and cartography, but involving local populations in the different stages of the process. The involvement of local populations, through the mobilization of their indigenous knowledge, significantly increases data quality and considerably reduces the costs and duration of the evaluation process. Ultimately, only 2% of the trees inventoried were “unknown” by local botanists, 92.3% of the species identified by them had accurate scientific correspondences. Help of local actors contributed to halving the time required to set up the plots and reduced the cost of operations by twenty times compared with using experts. REDD +, at least its local level monitoring dimension, could be successful if implemented in a dialectic involving expert scientists and local populations.