This work investigated morphology, structure and chemical transformation of forest residue chars devolatilized in a drop tube reactor at high heating rates and high temperature conditions. Produced forest residue chars were analyzed by SEM to examine morphology and structure variations. Compared to parent forest residues, char residues obtained from devolatilization experiments have significant smaller particle sizes. At 1200°C, the char particle underwent plastic deformation, developing a structure with smooth and compact surfaces. EDX analyses of the char surfaces revealed migration and coalescence of inorganic elements (mainly Ca, K and Si) during devolatilization processes. It was found that vaporization of calcium from char particles is more intensive at 1200°C compared to that of 800°C char. Meanwhile, part of calcium retained the char residues and incorporated into silicates structures. © 2015 The Authors. Published by Elsevier Ltd.