This paper addresses whether synergistic interaction or additive behavior govern the co-combustion characteristics of lignite and biochars produced from hybrid poplar (HP), ash tree (AT), and rhododendron (RH). The biochars were blended with lignite and the burning behavior was investigated by thermal analysis. Upon carbonization, fundamental change occurred in the burning mechanisms of biomass from homogeneous to heterogeneous reactions. Blending the lignite with biochars led to improvement in the calorific value and reductions in the ash yield. Carbonization limited the high reactivity of biomass, and the reactivities of biochars became closer to the lignite's reactivity, consequently they burned in accord without segregation.