what does it mean?

[tomcao]

Some environmentalists question the prudence of exploiting features of the environment, arguing that there are no economic benefits to be gained from forests, mountains, or wetlands that no longer exist.

[Tdol]

If you exploit the feature, you destroy it, and then the economic benefit dries up.

[susiedqq]

Are you sure you copied this sentence correctly?

To me it makes more sense as:

Some environmentalists question the prudence of not exploiting features of the environment, arguing that there are no economic benefits to be gained from forests, mountains, or wetlands that no longer exist.

[tomcao]

yes, i copied it correctly.

[tomcao]

My understanding:

There is no need to protect the features of environment which no long exist, because there is no economic benfits to do that.

[susiedqq]

Some environmentalists question the prudence of exploiting features of the environment, arguing that there are no economic benefits to be gained from forests, mountains, or wetlands that no longer exist.

I guess it is the word exploiting that confused me.

IMHO, "exploiting" a natural setting would be like turning a forest into a parkland and charging money to get in. In that case, there is economic benefit, and the environment still exists. (Although not in its original state)

I would have used the word "altering" or "re-defining." Once a wetland is altered, it no longer serves its purpose and no longer exists.