This will only work if you change your config file to allow fillers to drop items when clearing, or if you are using a version prior to 3.4.0.
You can make an efficient tree harvesting setup by using a Clear-Pattern Filler, obsidian pipes, and your favorite tree-harvesting pattern. For a 20x20x8 tree farm, you will need 16 Obsidian Pipes, 17 Combustion Engines, a Filler, 9 Glass for the Clear Pattern, 1 TNT or other easily breakable material to restart the Filler, and 4 landmarks. Fairly expensive in terms of initial setup but this will reap rewards as long as you never leave it on accidentally.
Place your Landmarks such that the Filler will create a 20 by 20 by 8 area. Change the blocks beneath the filler-area to dirt and place torches as required. Make sure there is a roof 9 blocks above you to prevent over-sized trees. Tunnel underneath your dirt floor and place obsidian pipes every 5 blocks, with a Combustion Engine powered by 1 bucket of Fuel directly underneath. You can then set up your redstone wiring and transportation pipes to a central location. Every 20x20 area should look like this:
XXXXXXXXXXXXXXXXXXXX XrrrrrrrXXXXrrrrrrrX XrOXXXXOXXXXOXXXXOrX XrpXXXXpXXXXpXXXXprX XrpppppIpIppIppppprX XrXXXXXXXpXXXXXXXXrX XrrrrrrrXpXXrrrrrrrX XrOXXXXOXpXXOXXXXOrX XrpXXXXpXpXXpXXXXprX XrpppppIpIppIppppprX X = Blank O = Obsidian Pipe p = Transportation Pipe I = Iron Pipe r = Redstone current powering engine under Obsidian Pipe
The main issue with using a filler is that the blocks drop to the floor when a clear pattern is used. However, a Combustion Engine on an Obsidian Pipe draws blocks from 5 blocks away which includes through other blocks. Therefore, using this setup you can use the filler to clear your trees and collect all of the drops with one revolution of a Combustion Engine. This maximizes fuel, requires no cooling, and is 100% resuable. Theoretically you do not even need a ceiling and can make a 100x100 block tree farm.
- Simply take one block of glass, or TNT if you don't want to waste your glass, out of the filler and place it back in to reset it to "harvest" mode
- Plant your trees
- Turn on your Filler and then turn it off when finished
- Press the button to turn on your harvesting engines for one revolution.
A note on this is that Birch and Pine trees both require more horizontal space, which means you may want to increase your tree farm size to 26x26 while only planting in the center 20x20 area. This is equally efficient as the Filler is smart and will not waste energy harvesting blank spaces.