To use in blender just go to file "Append" then navigate to the Firewood.blend file. Click on it go to object folder and take each firewood piece, taking the inner, bark, and transform objects for each firewood piece. Example: "Firewood_01Inner, Firewood_01Bark, Firewood_01Transform. This will give you the complete piece of firewood with the empty for transformations. 

To create broken pieces of bark Just duplicate a piece of firewood's bark object. Then use "Alt P" and clear parent to disconnect it from the empty. Now just go into edit and delete faces to bark a new broken piece of bark. For no bark on a pieces of wood just delete the bark object.