The current situation in the energy sector suggests the possibility of using biomass in co-combustion systems as an alternative to other fuels. In the case of the North of Spain the amount of forest residues that is generated guarantees it as a valuable source of energy for the future. However, an effective exploitation of these residues must first overcome a number of serious problems such as transport, storage, handling and pre-treatment, to meet the requirements of the power plants. The aim of this work is to study the influence of storage time on the moisture content and chemical and combustibility properties of pine woodchips. Their combustibility behaviour was evaluated by means of the following tests: heating value, ash composition, slagging/fouling indices, and the combustion profiles obtained from TG analysis. As a result of the weather conditions in the North of Spain open-air storage in the area under study is not suitable for dry pine woodchips, although their combustion behaviour remains practically unaltered. Work carried out with financial support from the Spanish MICINN (Project PS-120000- 2006-3, ECOCOMBOS), and co-financed by the European Regional Development Fund, ERDF. The assistance from staff at La Pereda power plant owned by HUNOSA, is also gratefully acknowledged Peer reviewed