The Appalachians are covered in trees, as are large swathes of the subtropical southeast.

Land tends to become forest if it has enough moisture, isn't suppressed by critters, and doesn't burn. Human forest fire suppression has tended to increase forest cover, although some of that is self-interest. Lots of tree farms out there, but the biodiversity of a quarter of identical-aged pine trees destined for the sawmill is nothing compared to an old-growth forest (or something disrupted by a tornado/fire/etc.)