Tree farming is one of the core mechanics of Forestry (not to be confused with Tree Breeding). With Forestry, you are able to completely automate the harvest of logs and saplings. Simply place an Arboretum in a well-lit area and watch as it automatically clears out the required area for your farm and lays down Humus and saplings. Add a Logger to your farm and it will automatically cut down your trees and collect saplings and apples, so you will never need to swing an axe again. You can use a Forester to kick your farm into overdrive by using catalysts to instantly grow your trees.
If you have IndustrialCraft² installed, you can also grow Rubber Trees and harvest their sticky resin using the machine called a Tree Tap.
Once you power this machine with enough BuildCraft energy, it will start to clear an 13×13 square area, and place humus in the same height of the machine itself, leaving a 9×9 square clear in the middle. Then it will start to plant saplings on it, and when these grow, the humus below them will turn to sand, the Arboretum will replace these, the sand will be picked up to its inventory. It needs to be supplied with humus and saplings, and it will output the sand to a BuildCraft pipe automatically. (You do not need to use a powered wooden transport pipe)
The Arboretum can only plant rubber trees, if IndustrialCraft² is installed.
The Logger will cut down any trees in a 21x10x21 (21 long, 21 wide and 10 high) area (only vanilla tree blocks, and IndustrialCraft² rubber trees) and pick up the apples and saplings from the ground. It needs to be powered by BuildCraft energy to work, and it will output the logs, the saplings and the apples from any side to a BuildCraft pipe, on an inventory, like a chest.
The Forester was a machine which was capable of hastening the growth of trees nearby. It has been removed in 2.1.x.x.