Carbon storage in forests is not permanent. The leading paradigm among negotiators of the Clean Development Mechanism (CDM) is that non-permanence should be addressed by an appropriate carbon credits accounting method. This paper reviews and discusses these methods and presents a model that calculates the minimum area that an hypothetical forest plantation project should have to be able to cover its transaction costs with the revenues from sales of carbon credits. The model compares different accounting methods under various sets of parameters on project management, transaction costs and carbon prices. Model results show that under current carbon price and average transaction costs, projects less than 500 hectares are excluded from the CDM, whatever accounting method is used. Temporary crediting appears to be the most favorable approach to account for non-permanent carbon storage in forests and also for the feasibility of smaller projects. However, the possibility of low price for credits with finite lifetimes is a risk that could prevent the establishment of CDM forestry projects. Plantation projects with low risk of unexpected carbon loss and sufficient capacity of insuring or buffering the risk of carbon re-emission would benefit from equivalenceadjusted average carbon storage accounting rather than from temporary crediting.