But one can practice skills without destroying vegetation that might take a year to regrow.
Longer, 20 or so likely. Yes you can practice many skills, but some are direct, how to fell, cut and split fresh woods is specific to that wood and even type and you can't get it aside from working with them. How specific vegetation induces cover. Large sheets of birch bark for example have a very different effect on repelling rain than dead and sparce boughs, or most ground litter.
Can you practice signal fires without tossing on green living wood and branches? Sure.
But without using such branches do you know how much flame/smoke they produce, do you know how far away it can be seen, do you know how long it lasts, or what it takes to ignite it, do you know the best way to cut it. I have seen someone for example throw an armload of green boughs on a fire and not realize the massive flame potential it will produce , inexperience and a quick wind change would be an unfortunate situation.
Again, I don't live where you do, and maybe your woods do not see the annual traffic mine does.
Rarely, outside of direct land next to houses or within an hours or so walk, it is basically never touched. Quite close to houses there is a lot of cutting done, usually by kids building cabins, so there is a lot of waste, trees cut off at 3' above the ground for example. But all of this is getting build up so fast that it makes no difference.
I can see a point that if everyone decided to go into the woods and chop down enough wood to make a leanto tomorrow then it would be likely that yes there would be a destructive influence and you can certainly be overkill in terms of chopping up things for entertainment without regard, however there is also ways to make a difference in a positive manner.
Wood lots for example have to be trimmed of damaged trees so you can do your part in removing these. You can also transplant trees. I found three really young maples last week growing along a road leading to a local graveyard which had no chance of surviving because they would be cut down once they overlapped the road assuming they actually survived being run over as they were basically on the sidewalk.
I transplanted them about a mile into the woods in a small clearing close to a place where I cut down a small birch awhile back because I wanted to work with the bark and the fresh wood. But again I can certainly understand a perspective which sees too much unnecessary cutting and I think you can go a long way in developing skills while minimizing cutting.
-Cliff