There used to be horses and camels native to North America by 1492 they were no more. Until the reintroduction of the horse, which allowed them to hunt and bring down one buffalo at a time they drove them over cliffs, One tribe of under 100 people slaughtered thousands of buffalo, most left to rot.
The deserts of the southwest used to be only semi-arid until they cut down so many trees that they caused climate change in that region.
The mound builders of the mid-west ruined their environment to the point that they died out from massive starvation. The reason the land was so green and lush when the settlers came along was that the local tribes that they met had just gotten there themselves.
In much the same way the Maya had deforested and stripped Central America. It took a couple of centuries for the land to recover.
I question what you call, lasting damage.
So far nothing on this scale of damage has been done since.
a.cricket
I call lasting damage, or lasting impact, our cities, freeways, homes, and development caused by millions of people... but if you want to blame the indians for all the "real" damage done to the environment, go for it. Just know that you are not living in reality any more than the wackos on the other side.
As for whether any particular piece of land being debated is truly "natural", I don't see what difference it makes. Wild lands either have intrinsic value as wild lands or they don't. I happen to believe that some large tracts of land should always be kept wild as a valuable public resource... but that doesn't mean humans must be kept out, or that once humans have set foot on it it is no longer natural, we are natural too. Wild lands protected for the public need to be enjoyed by the public and open to recreactional use and even logging, but that is different than building shopping malls on it. Whether people have been part of the history of landscape or not makes little difference in whether the land as it is now is worth protecting as it is, or not.