Dead trees are found in Quagmires, Dead Forests, and several other biomes. Dead wood can not be crafted into planks however it can still be cooked in a furnace to produce charcoal. Until 1.8 they didn't have saplings or leaves.
- You can melt deadwood to make charcoal, or
- You can make some buildings, since a single tree give you lot's of them.
- If you play with a modpack containing industrialcraft, Dead Wood can be used to make rotor blades for the windmill.