This is a one command that turns grass, dirt, stone, sand, bedrock, sandstone, mycelium, netherack and endstone into leaves. You have to get cobblestone for stone tools from naturally spawned structures. You can stop the decaying for 5 minutes by dropping blaze powder. It is laggy, so if you have a bad computer it may be hard to play.

Get the command at http://pastebin.com/EqK0mhr2. Paste this into a command block and power it for the machine.