national park vs parkland

national park and parkland both are nouns.

Word	Noun	Adjective	Verb	Adverb
national park	Yes	No	No	No
parkland	Yes	No	No	No

As nouns, parkland is a hypernym of national park; that is, parkland is a word with a broader meaning than national park:

national park: a tract of land declared by the national government to be public property
parkland: a large area of land preserved in its natural state as public property

Other hypernyms of national park include park.

national park (noun)	parkland (noun)
a tract of land declared by the national government to be public property	a large area of land preserved in its natural state as public property