When wood is burned, it turns to heat, chemicals and gases. Complete combustion produces water vapor and CO₂ along with non-combustible heat and ash. When combustion is incomplete, CO, hydrocarbons and other gases are formed.
Therefore, these logs suffered combustion, that is, heat was formed, with water vapor, CO₂ and ash if it was a complete combustion.
Wood + O₂ ----> CO₂ + H₂O (complete combustion)