scrub pine vs pine tree

scrub pine and pine tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
scrub pine	Yes	No	No	No
pine tree	Yes	No	No	No

As nouns, pine tree is a hypernym of scrub pine; that is, pine tree is a word with a broader meaning than scrub pine:

scrub pine: common small shrubby pine of the eastern United States having straggling often twisted or branches and short needles in bunches of 2
pine tree: a coniferous tree

Other hypernyms of scrub pine include pine, true pine.

scrub pine (noun)	pine tree (noun)
common small shrubby pine of the eastern United States having straggling often twisted or branches and short needles in bunches of 2	a coniferous tree