OK, so potentially it was a famous tree, but does that justify four years? Think about it, for cutting a tree down in the middle of nowhere.
That's a bit much - especially it wasn't for profit; but one way to think is the number of people the act pissed off; probably way more than would be annoyed by a nice tree in a small neighbourhood - but also, you have to punish something like that harshly to stop people actually doing it again.