The devolatilization behavior of pine and beech wood from carpentry residues and an herbaceous product from an energy plantation (artichoke thistle) was investigated by thermogravimetry. The effect of three pretreatments, hot-water washing, ethanol extraction, and a combination, were also studied. Various approaches based on first and nth order partial reactions in a summative model of pseudocomponents were employed to determine the best kinetic parameters that describe the experiments both at linear and stepwise heating programs. The assumption of four partial reactions appropriately described the global decomposition of most of the samples, while a low-temperature partial reaction was needed for the untreated pine. After the separate kinetic parameters for each of the samples were determined, a further check on the effects of the pretreatments was carried out by determining how a common set of activation energies describes the untreated and pretreated samples of the same feedstock.