The nature of which areas of the continent of North America is greatly changed as a result of economic activity?

In general, the nature of North America is significantly changed under the influence of human activities. The prairies of the mainland and the densely populated areas of the Great Lakes and the Appalachian Mountains have changed exceptionally.
The reason for the change of prairies in chernozem-like soils. At the moment, the area of distribution of the mentioned soils corresponds to the central section of the US corn belt, which is one of the main agricultural areas of the state (Iowa).

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