The stone pine (Pinus pinea L.) has thick bark as an adaptation to wildfire. In this study, laboratory tests were carried out to quantify the influence of bark thickness on flammability and fire resistance in this species. Heating rate in the cambium and the time to reach lethal temperatures in living tissues were determined using a mass loss calorimeter. In addition, data from permanent plots were used to generate linear mixed models to predict bark thickness along the trunk in stone pine stands. The combination of laboratory and field data provided information about the critical threshold of bark thickness (2 cm) below which the heat transmission rate would increase, decreasing the time to reach lethal temperatures in the cambium and therefore the resistance to fire. A new model was developed to calculate critical thresholds of charring height that guarantee efficient protection from fire along the trunk. Predicting whether the bark is thick enough to help trees survive may have important applications in the field of forest fuel management and in the ecology of these pine forests, as well as in preventive silviculture to assess critical heights of trunks likely to be affected during wildfire and prescribed burning.