Forest biomass as a source of renewable energy from wood energy plantations can produce carbon-neutral energy as fixed carbon is bound in biomass subject to harvest for energy substitution and the contributions to the soil. This type of forest plantations of short rotation, high density, and located usually on marginal land can become an excellent opportunity to produce fuel from biomass for a country. However, their sustainability has been questioned due to the increased frequency of harvests and moreover its short term benefits on the increase of carbon at soil level on marginal sites have been confronted. Wood energy plantations were established with Eucalyptus camaldulensis, E. nitens, E. globulus and Acacia melanoxylon at densities of 5 000, 7 500 and 10 000 trees per hectare, on two sites with contrasting forest soil production capacity (sandy and granite) located in the Biobío Region of Chile. The overall objective of this paper was to evaluate carbon sequestration in the soil profile as well as the sustainability of soil nutrients. The most promising results were observed at higher densities which are able to maintain a higher availability of nutrients; additionally it was possible to sustain carbon levels in the soil within the observation period of less than 4 years. Despite the above higher densities may reflect physiological changes for the species.