Why did some farming communities move after using swidden fields?

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A group of Native American men in colorful traditional regalia with feathered headdresses dance outdoors at a powwow ceremony on a grassy field. — Indigenous peoples of the Americas Performers at a Canadian powwow, c. 2008.

In the context of Indigenous peoples of the Americas, farming communities that practiced swidden agriculture—also known as slash-and-burn agriculture—relocated their settlements primarily when the productivity of their local fields or garden plots significantly declined.12

Because these systems relied on the burning of trees and shrubs to introduce nutrients into the soil, the fertility of the land was finite. Over time, as the soil became exhausted and the local supply of firewood diminished, communities would move to new areas to sustain their agricultural needs. While these swidden systems often maintained high ecological diversity, which helped prolong the usefulness of the land, the eventual depletion of resources necessitated the periodic relocation of the entire community.12