wilderness in general doesn't only contain trees..it contains habitats for animals and complex systems where one animal depends on the other.
If one species goes extinct another might go extinct as well and you can't just replace them.
I know, but if you plant new trees, can you not create/supply new habitats?
Yes, you create new habitats -- but it's no longer a wilderness.
Christina's right. Wilderness contains much more than trees. Here's the definition of wilderness from Dictionary.com.
"a wild and uncultivated region, as of forest or desert, uninhabited or inhabited only by wild animals; a tract of wasteland."
Once people have cut down trees or otherwise interfered with the wilderness, it's no longer a wilderness. Habitats for animals and other plants are disrupted, often to the point of no return.
So you're saying that when you create new habitats, it is no longer wilderness because of human interference?
Don't polluting gases occupy every inch of the atmosphere? Are they not above every living thing on this Earth? Doesn't human influence reach everywhere, even wilderness?
That's right. A wilderness has little if any human interference.
Your second statement is also correct. Polluting gases and polluted water harm our environment, including wildernesses. Remember your original quote from Aldo Leopold: "wilderness is a resource that can shrink but not grow." But pollution doesn't change a wilderness if there are no roads or human activity on the ground.
Well if you're saying creating new habitats makes something not wilderness becuase of human interference how can you say something is wilderness when you agree that polluting gases reach wilderness? Can't pollution change wilderness?