Well, fc, what I would consider
"Nature" writing isn't as important as the rubric under which I momentarily and conveniently ( and perhaps lazily) placed these two writers.
Hoagland and Abbey both became noticed when they wrote intensely observed narratives pointing up the incipient destructiveness and willful esthetic blindness among custodians of public lands.
Under that general heading both writers ( and many others like them), like Aldo Leopold ( "Sand County Almanac"), and, of course, Thoreau, have written in what I might call a "sustained state of reverence for the natural", which might be a memoir of a walk down Brice Canyon before the flooding, or the resentment instilled by the relaxation of regulations over industrial construction in the desert.
Matthiessen's "The Tree Where Man Was Born" ( see postings below) is part of this genre, I think.
I'm not thinking immediately of works like the animal poems of Marianne Moore, or "The Moose" by Elizabeth Bishop, just to name other pieces tied up in the theme of "nature" and human regard for its wonders. I certainly love those poems, of course.
I suppose I'm really talking mostly about landscape writing and its implications. So John McPhee and his beautifully crafted little books would certainly fit under the broad heading I'm trying to suggest.
Does that help? If not, help me!