gray alder vs alder tree

gray alder and alder tree both are nouns.

Word	Noun	Adjective	Verb	Adverb
gray alder	Yes	No	No	No
alder tree	Yes	No	No	No

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

gray alder: native to Europe but introduced in America
alder tree: north temperate shrubs or trees having toothed leaves and conelike fruit; bark is used in tanning and dyeing and the wood is rot-resistant

Other hypernyms of gray alder include alder.

gray alder (noun)	alder tree (noun)
native to Europe but introduced in America	north temperate shrubs or trees having toothed leaves and conelike fruit; bark is used in tanning and dyeing and the wood is rot-resistant