The type of figurative language he is using is a metaphor.
Step-by-step explanation
In Nature, Emerson describes the woods saying it's the plantations of God because he wanted to say, in a figurative way, that God grew everything, so the woods are his plantation too.
Metaphors, such as the one Emerson used, are figures of speech which describe actions/objects to explain an idea that isn't literally true.
Moreover, it is usually used in poetry or literature, like in this essay, to add life to the language.