Oil or biofuels?

Renton Righelato and Dominick V. Spracklen argue in Science that massive biofuel use would add more CO2 to the atmosphere than oil use (Carbon Mitigation by Biofuels or by Saving and Restoring Forests?):

[F]orestation of an equivalent area of land would sequester two to nine times more carbon over a 30-year period than the emissions avoided by the use of the biofuel. Taking this opportunity cost into account, the emissions cost of liquid biofuels exceeds that of fossil fuels.[...]

If the prime object of policy on biofuels is mitigation of carbon dioxide-driven global warming, policy-makers may be better advised in the short term (30 years or so) to focus on increasing the efficiency of fossil fuel use, to conserve the existing forests and savannahs, and to restore natural forest and grassland habitats on cropland that is not needed for food. In addition to reducing net carbon dioxide flux to the atmosphere, conversion of large areas of land back to secondary forest provides other environmental services (such as prevention of desertification, provision of forest products, maintenance of biological diversity, and regional climate regulation), whereas conversion of large areas of land to biofuel crops may place additional strains on the environment.