I didn't say if people do it it must be anti-nature, only that it usually is. We generally alter our environment to suite our needs, not to improve it. I can't think of many instances where our presence has benefited most of the plants and animals and left them better off then before we arrived; can you?
Who cares about them? That's not snark, I mean it seriously. Humans are intelligent creatures with desires. Trees are leafy lumps cellulose. They have no brain, they have no intellect - a tree cannot feel pain or pleasure, joy or sorrow. Sure, it can live or die, but that life has no moral content. The natural world is only valuable insofar as it's useful for creatures that actually are morally relevant - i.e., humans.
That's not saying we should pave the forests - forests are nice, I like having them around. But it's the human desire to have a forest that's meaningful, not the forest itself. If humans want houses more, then it's perfectly acceptable to knock down the trees, turn them into lumber, and build houses with them, and spit-roast the animals over a wood fire in the backyard for the housewarming party.
No.
"Humans are natural and since they build cars, cars must be natural as well?"
As I said, it's natural for people to build things, so building cars is natural.
I simply don't adhere to the PC view that if people do it, it must be anti-nature, unnatural, or bad (though sometimes that happens to be the case).