Introduction In the last 150 years, the world forest surface was re- duced in more than 65%, that is around 4.5⋅10 9 ha [1, 2]. One of most important causes of this considerable environmental deterioration corresponds to forest fires that, direct or indirectly, were originated in about 98% by man activities. In the Mediterranean zones, wildfires are the main and nearly exclusive responsible for the loss of forest covered surface. Since the last 90’s, Spain lost more than 200 000 ha of forest surface [3], thus be- coming the most affected Union European country, in front of Italy, Portugal, Greece and France. Particularly, in Galicia (NW Spain) with a forest surface representing 11% of the whole Spanish one, forest fires devastated around 40 000 ha per year [3]. To understand the meaning of the bulk environ- mental deterioration, it is necessary to analyze the eco- logical damage through: loss of forest resources and fertile soil and also an economical loss of 240 million euros per year, that were spent to prevent and fight for- est fires and also to recover degraded green spaces. To summarize, Spain has lost since the 1960’s more than 6 400 000 ha with an economical damage of around 4.5⋅10 10 € [3]. One of the modern strategies to fight forest fires consists in the design of risk indices [1, 2, 4–6]. These risk indices try to guess the behaviour of the different forest species before forest fires, depending on their vegetative state and the environment in which they grow up. These indices can be elaborated by combi- nation of many factors associated to the starting and spreading of forest fires and help to avoid or fight wildfires in the most effective way. Objectives In the present study, forest fires were considered as physical processes depending on three basic fac- tors [1, 2, 7]: a fuel, oxygen and temperature (without taking into account the accidental or planned cause). One of the main objectives of this study was the search for a new risk index that incorporate all the known risk indices basically based on physical environmental con- ditions, that up to now were used independently. A risk index can be defined as a numerical value that can be calculated from many parameters integrated into a cu- mulative final value that represents the physical state of a fuel to initiate and/or spreading forest fires. By in- tegrated, we understand an interaction among many parameters that have influence both on the ignition or beginning of the wildfire (ignition risk index), and on the capacity to spread fire (spreading index), that have been for long studied separately. Cumulative means the fractional contribution of both of these indices to the final value of the risk index. 1388–6150/$20.00 Akadémiai Kiadó, Budapest, Hungary © 2005 Akadémiai Kiadó, Budapest Springer, Dordrecht, The Netherlands Journal of Thermal Analysis and Calorimetry, Vol. 80 (2005) 457–464 ENERGETIC STUDY OF RESIDUAL FOREST BIOMASS USING CALORIMETRY AND THERMAL ANALYSIS L. NúÔez-Regueira * , J. A. Rodríguez-AÔón, J. Proupín, B. MouriÔo and R. Artiaga-Diaz Research Group TERBIPROMAT, Department of Applied Physics, Faculty of Physics, Universidade de Santiago de Compostela (U.S.C.), 15782 Santiago de Compostela, Spain The European policy on energy focus on the search for alternative and renewable sources of energy where forest biomass plays a significant role. In this article, calorific values of different kinds of forest residues (leaves, thin branches, barks, etc.) are reported. These values were measured by combustion bomb calorimetry with the objective of understanding, through different risk indices, the behaviour of forest waste in the case of wildfires, and also to study the use of forest residues as raw materials to be used as energy sources. The study was complemented with determination of elemental analysis, flammability using a standard epiradiator, thermodegradation analysis, and different mechanical tests trying to get relationships between thermal behaviour and some physical properties. The study was carried out on Eucalyptus globulus Labill and Pinus pinaster Aiton, because these forest formations have both high economical and ecological interest in Galicia (NW Spain). Keywords: calorific value, calorimetry, flammability, forest fire, risk index, thermal analysis, xyloenergy * Author for correspondence: falisar1@usc.es