seaside alder vs alder tree

seaside alder and alder tree both are nouns.

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

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

seaside alder: shrub or small tree of southeastern United States having soft light brown wood
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 seaside alder include alder.

seaside alder (noun)	alder tree (noun)
shrub or small tree of southeastern United States having soft light brown wood	north temperate shrubs or trees having toothed leaves and conelike fruit; bark is used in tanning and dyeing and the wood is rot-resistant