After nearly nine years, life is returning to ground zero in a tangible way.

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

Eventually the green sanctuary 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 New Jersey nursery, the 16 trees were being loaded onto eight tractor—trailers at midnight Friday for the 35—mile (56—kilometer) trip to Manhatan. Cranes were to set them into place on 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 Sept. 11 victims’ families and visitors. Benches will invite visitors to linger and walk along its cobblestone and stone pavers accented with plantings and low ground cover.

The memorial plaza will essentially become is a rooftop garden, built atop the deep chasm left by the destroyed towers on Sept. 11, 2001. The museum commemorating the 2001 attacks, commuter train platforms and a parking garage are being built as far as 70 feet (21 meters) below ground.

Cox’s company has been irrigating and fertilizing the indigenous trees for four years on the 15—acre nursery in Millstone, New Jersey. The location was selected to allow the trees to acclimate to the “tough, windy and cold” environment in lower Manhattan,” he said.

Mr. Cox was given strict criteria for selecting the trees, including that they be “soldier—like in appearance” and come from New York, Maryland, Pennsylvania, and Washington D.C., the places impacted by the terrorist attacks.

The swamp white oaks were also chosen for their durability and colour, especially for their amber and golden brown hues in autumn and as symbols of life and regeneration.

The trees have more than doubled in size during their time at the nursery, and eventually will soar to 60 to 80 feet (18 to 25 meters).

Once they are planted, an arborist will work full—time to make sure the oaks won’t suffer damage from the dust and clutter of construction that goes on every day at the site, where two skyscrapers and a transit hub are also being built.

“These trees are going into a Garden of Eden condition,” said Mr. 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 from a computer through sensors embedded into the root ball of each tree.

Tree “sheriffs” will monitor the trees’ health and “construction managers” will watch for dust and debris damage from the surrounding construction site, Mr. Cox said.

“I would say that our expectations are we will have 100 percent survival of the trees on the site,” he said.

Keywords: Ground zero

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