I'm looking for a concise term, already in use in music writing or analysis, for a composition that evokes nature. I don't want to use "pastorale" because of its usual association with herders and grazing domestic animals.
Some well-known examples might be Grofé's Grand Canyon Suite or Mussorgsky's Night on Bald Mountain.
We could coin something. But 'already in use in music writing or analysis' is tricky! You might have to accept the answer 'there isn't one'.
There's an entire field of musical study called ecomusicology. It's mainly about the outlook of the scholar, examining the relationship between musical phenomena and the environment, but it would definitely be interested in a work that consciously references or positions itself in relationship to the natural world.
So you can't quite use it the way you want—"Grand Canyon Suite is a work of ecomusicology"—but it sounds like researching this field would help inform whatever you're working on. And while Grofé and Mussorgsky are earlier than the term, you could certainly use it when talking about a work that is consciously created within an awareness of ecomusicology.
If I may broaden the request slightly, what you're discussing falls into the realm of what we call "topic theory," a sub-branch of semiotics (the study of "signs").
In topic theory, certain musical symbols (or signs) act as "topics" to evoke a particular idea: a group of horns suggest a "hunting" topic, the siciliano rhythm (dotted eighth, sixteenth, eighth) suggests a "riding" topic (e.g., a horse), etc.
Within this concept, there are clear pastoral topics: maybe strings that indicate a babbling brook, or English horns that could indicate grazing animals.
So although "topic theory" is not completely synonymous with pastorale/idyll narratives, the latter are clearly a part of the former.
