As a result of the 1997 Kyoto Protocol, afforestation of agricultural lands can be expected to take on an important role in the CO2-emissions reduction policy arsenal of some countries. To date, identification of suitable (marginal) agricultural lands has been left mainly to foresters, but their criteria fail to take into account economic nuances. In this study, an optimal control model is used to determine the optimal level of afforestation in the western Canada. The results indicate that, while planting fast–growing trees for carbon uptake on marginal agricultural land may be important, the path dynamics matter in determining whether Canada can rely on afforestation to meet its obligations under Kyoto