NEW YORK (AP).- After nearly nine years, life is returning to ground zero in a tangible way.

Sixteen swamp white oaks arriving Saturday are the first of nearly 400 trees that will be planted at the World Trade Center site, where more than 2,700 people were killed when terrorists attacked the twin towers on Sept. 11, 2001.

The trees will dot a cobblestone plaza surrounding two huge pools built on the footprints of the destroyed towers.

"After all the tragedy, the idea of the first living component going back is emotionally significant to the rebuilding process," said Tom Cox, CEO of Environmental Design, the Houston company that has cared for the trees and is taking them to the trade center site.

Cultivated for four years at a nursery in Millstone, N.J., the 16 trees were to be loaded onto eight tractor-trailers at midnight Friday for the 35-mile trip to Manhattan. Cranes were to set them into place Saturday morning before crews plant them on the eight-acre memorial plaza.

Joe Daniels, president of the memorial foundation, called the trees' arrival "a big milestone ... after nine years of both recovery and construction."

Designers Peter Walker and Michael Arad envisioned a peaceful green space that would bring solace to visitors. Benches are an invitation to linger amid a walk along the cobblestone and stone pavers accented with plants.

The memorial plaza will essentially become a rooftop garden, built atop the deep chasm left by the destroyed towers. It will cover the museum commemorating the 2001 attacks, commuter train platforms and a parking garage that are being built as far as 70 feet below ground.

Cox's company has been irrigating and fertilizing the indigenous trees for four years at the 15-acre nursery, selected to allow the trees to acclimate to the "tough, windy and cold" environment in lower Manhattan," he said.

Cox was given strict criteria for selecting the trees, including that they be "soldier-like in appearance" and come from New York, Pennsylvania and Washington, D.C. — the places where the attacks hit.

The swamp white oaks were also chosen for their durability and color, especially for their amber and golden brown hues in autumn, and as symbols of life and regeneration. The trees will soar to 60 to 80 feet high.

Once they are planted, an arborist will work full-time to prevent the construction site's daily dust and clutter from damaging the oaks.

"These trees are going into a Garden of Eden condition," said Cox.

An elaborate subterranean irrigation system, with individual tubes running to each tree, will water and fertilizer the grove. The trees' condition, soil moisture and temperature can be monitored remotely through sensors embedded into their root balls.

"Our expectations are we will have 100 percent survival of the trees," Cox said.

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Associated Press writer Amy Westfeldt contributed to this report.




Copyright 2010 The Associated Press.