Pre-Columbian North America was no eden.

The popular image of pre-Columbian North America is of a pristine paradise. However, when Europeans first arrived in North America, they found anything but a primeval landscape. Instead, they encountered a land significantly altered by humans through the use of fire, sophisticated agricultural techniques, mining, and road and mound building, according to University of Wisconsin-Madison geographer William Gartner.

From fire-maintained prairies and altered forests to earthworks and settlements, the American landscape by the time of European contact already had endured thousands of years of modification by large Native American populations. The pristine view, according to Gartner and others, to a large extent is the invention of 19th-century romanticist and primitivist writers like Henry David Thoreau and Henry Wadsworth Longfellow. The reality is that the impact of native peoples was nearly ubiquitous, even in areas with comparatively sparse Indian populations.

Many scholars now believe there were between 40,000,000 and 80,000,000 inhabitants of the New World when Christopher Columbus first set sail on his voyages of discovery. "Indigenous peoples routinely cleared the ... landscape with fire," Gartner explains. "They burned to facilitate hunting and game drives, clear village and agricultural lands, assist in fuel-wood cutting, improve visibility and overland travel, manage pests, and facilitate warfare."

For example, the climate responsible for the...