Long before the first Europeans arrived, Indians had dramatically changed thelandscape of the eastern United States, a team of scientists has discovered.

For 5,000 years, native people had been cutting down trees and planting fields. They destroyed large tracts of pristine wilderness, replacing them with trees and plants that thrive on human disturbance.The impact of this widespread prehistoric farming, extensively documented for the first time in the United States by a team of archaeologists, ecologists, geologists and botanists, challenges the notion that Indians lived in harmony with the environment.

It also raises questions about efforts to preserve land in its "natural" state. If people have been changing the landscape for thousands of years, who is to say what is natural?

The implications for wilderness management are "quite important," said Hazel R. Delcourt of the University of Tennessee, who presented the results of the team's study at a recent conference of the Association for Tropical Biology.

Many wilderness areas are supposed to be maintained as they were at the time of European settlement, she said. "The assumption was that it was wilderness untouched by human activities."

But now it looks as though Indians had profoundly changed the landscape by clearing forest and planting crops, she said. In some places, they may have maintained meadows for their favorite game animals by periodically burning the grass.

The team turned up evidence for these practices in grains of pollen, charcoal from ancient hearths and nuts and seeds left over from prehistoric meals.

Kenneth L. Cole, a paleoecologist at the Indiana Dunes National Lakeshore, called the study "remarkable work."

"This is the kind of thing I like to see," he said, "because most ecologists have the naive belief that when Columbus got to North America, it was absolutely pristine, untouched by human hands - as if the Indians weren't human."

Research already had shown how prehistoric hunters and farmers changed the face of Europe. But many scientists assumed that native people left almost no mark on North America, and their studies of this continent started to blossom only in the past decade.

In 1967, a team led by Jefferson Chapman of the University of Tennessee began investigating the archaeology of Little Tennessee River Valley, which has since been flooded by the Tellico Dam.

The team uncovered hundreds of archaeological sites left by peoples who had lived in the valley for 12,000 years. It examined more than 31,000 bits of burned wood and 17 pounds of charred fruits, seeds, nut shells and crop plants from Indian hearths.

In addition, Hazel Delcourt and her geologist husband, Paul, dug down into layers of sediment in small ponds to find fossilized pollen grains that reflected changes in vegetation.

They discovered that 10,000 years ago, a forest of oak, chestnut and other hardwoods covered the river valley.

People began to settle along the rich flood plain next to the river, and 5,000 years ago they began to farm, planting squash and domesticating native plants such as marsh elder, sunflower and amaranth. By 1,700 years ago they were planting corn, and their fields had spread to less fertile land more than a mile away from the river, the team found.

Agriculture reached its height in the Mississippian culture, which flourished from 1,000 to 500 years ago. Villages and fields filled the river valley; farmers even cultivated ridge tops 1,000 feet above the valley floor.

Fields were quickly drained of nutrients and abandoned, to be invaded by weeds and by evergreen trees such as the pine and the Eastern red cedar.

This second round of growth was what greeted the first European explorers, Paul Delcourt said.

Similar changes probably took place in the fertile river valleys over a wide area of the eastern United States, the couple said.