This papers aims to determine the optimal rotation and the best alternative use of a forest stand when wood price is assumed to follow a Geometrical Brownian Motion and the externality generated by the forest capacity to reduce the level of carbon dioxide in the air is adequately taken into account. It is shown that the decision-making of cutting the trees depends heavily of the use which will be made of the harvested wood. The results of the model indicate what follows:

• The socially optimal rotation is higher than the optimal age of cut from the point of view of a private owner if stored carbon is released at the time of (or after) harvest;

• Rotation is shorter if carbon remains locked at the time of (and after) the cut than in the case of its release;

• The forestry becomes socially more profitable; one passes to the alternative use only for high site values associated with weak stumpage prices achievements.