[Natsu]

In Minecraft, cobblestone generators are highly viable and much better than mining, in fact. High-density tree farms are a lot more sustainable, too. Examples of both are on the wiki.

If you really need to speed up the tree farms, even though they're a lot better than harvesting wild trees, get bonemeal by creating a trap around an enemy spawner. Or just create a giant dark pit where water feeds the monsters into a trap in the center (either a pitfall or a lava blade). Again, it's all on the wiki. Infinitely sustainable. I've made all of these, except for the enemy trap, which I'm still working on... by using the cobblestone generator.