old growth vs virgin forest

old growth and virgin forest both are nouns.

Word	Noun	Adjective	Verb	Adverb
old growth	Yes	No	No	No
virgin forest	Yes	No	No	No

As nouns, old growth and virgin forest are synonyms defined as:

old growth and virgin forest: forest or woodland having a mature or overly mature ecosystem more or less uninfluenced by human activity

old growth (noun)	virgin forest (noun)
forest or woodland having a mature or overly mature ecosystem more or less uninfluenced by human activity	forest or woodland having a mature or overly mature ecosystem more or less uninfluenced by human activity