This database does not use Library of Congress Subject Headings, but its own controlled vocabulary. This is true for many databases. However, it is also true that the subject headings (sometimes referred to as subjects or descriptors) used in databases will often be similar (if not the same) as the Subject Heasings in our library catalog.
In MLA, you can try searching by subject for:
"Treatment of nature"
"Treatment of Environment"
Ecology AND Poetry
This is not a comprehensive list. There is a good chance you will find additional subject headings which also relate to the ecocriticism, or the intersection of the environment and literature.
Because this database is a large, interdisciplinary database - and not strictly a literature, or even humanities, database - I would add terms such as liter* (for literature or literary) and/or crit (for critiques or criticism) to my searches.
You can't search by Subject Heading in JSTOR or ProjectMuse. In JSTOR, you can narrow your search by asking the database to search for words in the abstract. In ProjectMuse, you need to search the entire content of the aritcle. For that reason, I would try searching for specific words or combinations of words:
Ecol* AND Liter* AND Crit.*
In JSTOR it can be heloful to narrow your search to English (or another language you are fluent in) as so many articles are written in languages other than English.
2) Another approach to finding articles is to look in the databses for Environmental Studies. The articles you pull up searching these databases could have a somewhat different focus, or angle, than the articles pulled up in the Literaure or Humanities databases. For example, they may look at the field of ecocriticism from the perspective of conversation (for example, how the development of ecocriticism has affected conservation efforts). They may also evaluate how the natural world in works of literature using the lens of a different discipline (Enviornmental Science or Conservation Biology). You probably won't find the wealth of articles in these databases that you do in the literature or humanities databases (and you will most certainly get more false results), but it is worth searching them to gain this different perspective.
You can try searching by by these Subject Headings (also called Subject Terms):
Nature AND Literary
"Ecology in Literature"
'... international literature in linguistics and related disciplines in the language sciences...covers all aspects of the study of language including phonetics, phonology, morphology, syntax and semantics...'
Linguistics & Language Behavior Abstracts (LLBA) abstracts and indexes the international literature in linguistics and related disciplines in the language sciences. The database covers all aspects of the study of language including phonetics, phonology, morphology, syntax and semantics.