forest vs tree farm

forest and tree farm both are nouns.

As nouns, tree farm is a hyponym of forest; that is, tree farm is a word with a more specific, narrower meaning than forest:

forest: land that is covered with trees and shrubs
tree farm: a forest (or part of a forest) where trees are grown for commercial use

Other hyponyms of forest include greenwood, riparian forest, silva, sylva.

forest (noun)	tree farm (noun)
the trees and other plants in a large densely wooded area	a forest (or part of a forest) where trees are grown for commercial use
land that is covered with trees and shrubs

forest (verb)	tree farm (verb)
establish a forest on previously unforested land