This is what it looks like where I live in mature saw timber mixed oak woods. These pics are not the greatest, but you can see the cleared section of the park on the left, and the uncleared private land on the right. It's like night and day. Sadly, much of PA looks like the cleared section on the left. But while the park shown here was cleared by people physically removing the underbrush, in the wilds of PA the deer have eaten it out of existence and continue to keep it in that suppressed state.
On the private land you can see about 20 yards until your view begins to be blocked by vegetation
Where the park stops and the private land begins, there is an obvious wall of natural vegetation.
These are just a few of the items in the understory