You might fail camo on plains, but you're perfect in forest/mountain/cave. Don't think you can even attempt to creep into or through plains (but hills works ok, I think) at that point, and you get a message like "the foliage is too sparse" if you try.

That should go away when you get to "at home" wilderness time. IIRC you can herb more places when you get to max wilderness as a mountaineer, too.