Sentence:  This means subduing and taming the forest itself—the central drama of "The Fields"—performing the hard labor of hacking the trees and “<WSD>niggering</WSD>” and burning the butts in order to get to the rich black soil underneath. 
Meaning of the word marked with <WSD> tags:  To clear land by laying light pieces of round timber across the trunks of the trees and setting fire to them at the point of contact, by which means the trees are slowly burned through.