Minecraft wiki entry for Tree_farming, associated text: Several mobs in the game can break blocks, and most of them have been used for wood farming. An overly complex design featuring creepers was made, but the insane size of it makes constructing it anywhere exceptionally difficult. A different design that uses ghasts is also available and much simpler to make, however when ghasts break blocks they destroy (without dropping) most of them, making tree farming with the ghast extremely inefficient.