timberline vs tree line

timberline and tree line both are nouns.

Word	Noun	Adjective	Verb	Adverb
timberline	Yes	No	No	No
tree line	Yes	No	No	No

As nouns, timberline and tree line are synonyms defined as:

timberline and tree line: line marking the upper limit of tree growth in mountains or northern latitudes

Other synonyms of timberline include timber line.

timberline (noun)	tree line (noun)
line marking the upper limit of tree growth in mountains or northern latitudes	line marking the upper limit of tree growth in mountains or northern latitudes