plant vs afforest

plant is a noun but afforest is not a noun.

As verbs, afforest is a hyponym of plant; that is, afforest is a word with a more specific, narrower meaning than plant:

Other hyponyms of plant include root, puddle, checkrow, bed, dibble, forest, replant, tree.

plant (noun)	afforest (noun)
buildings for carrying on industrial labor
(botany) a living organism lacking the power of locomotion
an actor situated in the audience whose acting is rehearsed but seems spontaneous to the audience
something planted secretly for discovery by another

plant (verb)	afforest (verb)
put or set (seeds, seedlings, or plants) into the ground	establish a forest on previously unforested land
fix or set securely or deeply
set up or lay the groundwork for
place into a river
place something or someone in a certain position in order to secretly observe or deceive
put firmly in the mind