Important factors in the evaluation of fire severity are the duration of the soil exposition to a certain temperature as well as the factors that determine the thermal transmissivity on the soil (moisture, texture, organic matter content, etc.). The aim of this work was to apply the degree-hours method (DH) to characterize the thermal impact of forest fires in soils. Thermal treatments in the laboratory were conducted using soil samples in order to study the effects in the soil exchange complex. The results showed the effect of the supplied degree-hour (DH) on the cation exchange capacity (CEC), which was expressed by a continuous exponential decrease in the CEC. This function may better explain the process of the decreasing of CEC than only the maximum temperature values. The sum of cations extracted in relation to the thermal treatment gradually increased with temperature or DH, and tended to stabilize at high values. The concentration of the different cations extracted increased gradually with the intensity of heating, and when related to the DH appeared to fit an equation of the type y=a+bxc with a high degree of confidence. Analyses of the results show that the measurement of the heat supplied to the soil is a useful parameter with which to interpret pedologic changes, especially when those changes happen continuously over time.