Porcupines have been around northern Wisconsin a whole lot longer than humans.
The forests did fine all that time.
15,000 years ago, there was nothing but mile high glacial ice in Northern Wisconsin.
Humans and porcupines moved in about the same time.
I’ve spent a lot of time in porcupine country. I’ve seen two trees that they’ve nibbled, both hemlocks. Too much other stuff to eat in coastal Oregon for them to be a problem. Mountain Beavers( boomers)on the other hand....But in all honesty, bear and elk, and deer kill more trees than the rodents do.