western hemlock vs west coast hemlock

western hemlock and west coast hemlock both are nouns.

Word	Noun	Adjective	Verb	Adverb
western hemlock	Yes	No	No	No
west coast hemlock	Yes	No	No	No

As nouns, western hemlock and west coast hemlock are synonyms defined as:

western hemlock and west coast hemlock: tall evergreen of western North America; commercially important timber tree

Other synonyms of western hemlock include Pacific hemlock, Tsuga heterophylla.

western hemlock (noun)	west coast hemlock (noun)
tall evergreen of western North America; commercially important timber tree	tall evergreen of western North America; commercially important timber tree