Here's when I would switch to a different tree. Oaks: 21 woodcutting where you can buy a mithril axe. It comes down with a real fast pace with a mithril axe. Willow: 41 woodcutting for woodcutting because at 41, you unlock the ability to use the rune woodcutting axe and is probably the only axe that you can really do some bussiness with willows. With other axes, it comes down at a quite slow pace and you wuld struggle with it with all the higher levels chopping. Yews: 75-80+ woodcutting: At this level, willows should come down quite fast with your rune axe, so it is a very good training tool as it comes down fast and you get a decent exp of 67.5 per log. Once you hit 75, you could start yews, but you might still struggle with it as yews are naturally a hard tree. At 80+ woodcutting, the pace of yew logs will come down within a reasonable pace (1 per 3-5 seconds). I hope this helps you and happy woodcutting. :)