mountain birch vs Western birch

mountain birch and Western birch both are nouns.

Word	Noun	Adjective	Verb	Adverb
mountain birch	Yes	No	No	No
Western birch	Yes	No	No	No

As nouns, mountain birch and Western birch are synonyms defined as:

mountain birch and Western birch: birch of western United States resembling the paper birch but having brownish bark

Other synonyms of mountain birch include Betula fontinalis, swamp birch, water birch, Western paper birch.

mountain birch (noun)	Western birch (noun)
birch of western United States resembling the paper birch but having brownish bark	birch of western United States resembling the paper birch but having brownish bark