In this paper are reported changes in heat values (HV) with the seasons of the year for the different species which make up most of the undergrowth in Galicia (Spain). Knowledge of these values is essential when evaluating the possibility of exploiting the energy content of the bushes in energy-recovery plants. The calorific values of combustion at 25 degrees C were measured by static-bomb calorimetry for forest residues originated in activities related to afforestation, firebreaks, forest clearing etc. From combustion experiments, the mean calorific value was found to be close to 19000 kJ kg(-1), similar to the calorific values of municipal solid waste (MSW). For this reason, these forest residues can be used as an additional fuel to be added to MSW in energy recovery plants and this will also minimize the risk of forest fires.