Columbia, La. ? The Army Corps of Engineers is on a mission to chop down every tree in the country that grows within 15 feet of a levee — including oaks and sycamores in Louisiana, willows in Oklahoma and cottonwoods in California.

The corps is concerned the trees’ roots could undermine barriers meant to protect low-lying communities from catastrophic floods like the ones caused by Hurricane Katrina.

An Associated Press survey of levee projects nationwide shows that the agency wants to eliminate all trees along more than 100,000 miles of levees. But environmentalists and some civil engineers insist the trees pose little or no risk and actually help stabilize levee soil.

Thousands of trees have been felled already, though corps officials did not have a precise number of how many will be cut.

The corps has “this body of decades of experience that says you shouldn’t have trees on your levees,” said Eric Halpin, the agency’s special assistant for dam and levee safety.

The saws are buzzing despite the outcry from people who say the trees are an essential part of fragile river and wetland ecosystems.

“The literature on the presence of vegetation indicates that it may actually strengthen a levee,” said Andrew Levesque, senior engineer for King County, Wash., where the corps wants trees removed on the six rivers considered vital to salmon populations.

The anti-tree policy arose from criticism directed at the corps after Katrina breached levees in New Orleans in 2005. The agency promised to get tough on levee managers and improve flood protection.

In 2006, the corps began sending hundreds of letters to levee districts across the nation, ordering them to cut down “unwanted woody vegetation,” a prospect that could cost many of the districts millions of dollars each in timber-clearing expenses.

Inspectors began an inventory of the levee system and told districts to fill in animal burrows, repair culverts and patch up erosion.

If they fail to comply, the agencies risk higher flood insurance premiums and a loss of federal funding.

“The corps’ new edict was regarded as a major change in policy,” said Ronald Stork, senior policy expert with California Friends of the River in Sacramento. “Something that is cheap and inexpensive is a chain saw. It was something to do that didn’t cost a lot of money that made you feel better.”

Last summer, the cutting crews came to Columbia, La., on the wooded Ouachita River levee at Breston Plantation, an 18th-century French colonial estate.

The plantation is surrounded by sycamores, live oaks, elms, pines, cedars, magnolias and crepe myrtles. Hundreds of trees grow within 15 feet of the levee. In theory, they would all have to go.

But after months of negotiations with landowners and the Tensas Basin Levee District, the corps agreed to let the district chop down only a few dozen trees on the levee.

“We don’t know how long the trees have been here, but they’ve never caused any problem up until now,” said Hugh Youngblood, 61, whose ancestors came to Breston in the 1800s.