subalpine fir vs Alpine fir

subalpine fir and Alpine fir both are nouns.

Word	Noun	Adjective	Verb	Adverb
subalpine fir	Yes	No	No	No
Alpine fir	Yes	No	No	No

As nouns, subalpine fir and Alpine fir are synonyms defined as:

subalpine fir and Alpine fir: medium-tall timber tree of the Rocky Mountains having a narrowly conic to columnar crown

Other synonyms of subalpine fir include Abies lasiocarpa.

subalpine fir (noun)	Alpine fir (noun)
medium-tall timber tree of the Rocky Mountains having a narrowly conic to columnar crown	medium-tall timber tree of the Rocky Mountains having a narrowly conic to columnar crown