Extending timber rotations: carbon and cost implications

A number of studies have suggested that incentives for carbon sequestration could lead to longer rotation periods for even-aged managed forests. In this article we examine the potential costs and quantity of sequestered carbon from extending rotation ages in softwood forests of the southern and western USA. A model of optimal rotations when carbon is a valued asset was developed to show how optimal rotations adjust when carbon is priced. Data on 324 types and site classes of softwood forests in southern and western states of the USA were used to examine the costs of extending rotations. The results were then aggregated by applying the marginal cost curves to inventory data within each county in these states. The results indicate that in these 12 states, about 15 million tCO₂ could be sequestered for less than $7/tCO₂ (1 tCO₂ = 1,000 kg CO₂), although for substantially higher carbon prices of $55/tCO₂, up to 209 million tCO₂ could be sequestered. Timber prices were found to have an important influence on the marginal costs of carbon sequestration, with site quality being of secondary importance. The results also showed that at $55/tCO₂ potentially 1 million ha of softwood forests could be set aside, mostly in the western states.