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Moving a Giant

The logistics of excavating(挖掘)and relocating a town's century-old, living sequoia(红杉)tree. Inhabitants of Boise, Idaho, watched with trepidation earlier this year as the city's oldest, tallest resident moved two blocks. The 105-year-old sequoia tree serves as a local landmark, not only for its longevity but also because renowned naturalist and Sierra Club cofounder John Muir provided the original seedling. So, when Saint Luke's Health System found that the 10-story-tall conifer(针叶树)stood stood in the way of its planned hospital expansion, officials called tree-moving firm Environmental Design.

The Texas-based company has developed and patented scooping and lifting technology to move massive trees. Weighing in at more than 800,000 pounds, the Boise sequoia is its largest undertaking yet. "I (had) lost enough sleep over this," says David Cox, the company's Western region vice president—and that was before the hospital mentioned the tree's distinguished origin. Before the heavy lifting began, the team assessed the root system and dug a five-foot-deep cylinder, measuring 40 feet in diameter, around the trunk to protect all essential roots. After encapsulating the root ball in wire mesh, the movers allowed the tree to adapt to its new situation for seven months before relocating it. The illustration details what followed. —Leslie Nemo

1. Mark A. Merit and his team at Environmental Design installed underneath the root ball a platform of seven-inch-diameter, 44-foot-long steelbars and, just below the rods, a first set of uninflated airbags (shown in gray). The team also dug a shallow ramp.

2. In roughly 15 minutes, the movers inflated the airbags to about three feet in diameter to raise the root ball to the surface of the hole.

3. By underinflating the front bags, the team allowed the platform carrying the tree to roll up the ramp and out of the hole while staying level. A trailer hauled the tree along as team members removed the airbags from the back of the platform and replaced them in the front. They repeated the process until the tree arrived at the edge of its new home.

4. There a second set of partially inflated bags (shown in white) waited inside the hole. Soil surrounding the sequoia in its original location was relocated as well, because trees are more likely to survive a transplant when they move with their original soil.

5. Using the first set of airbags, the movers rolled the platform into the new hole.

6. The bags waiting there were then inflated further to take the weight of the sequoia while the transportation bags were deflated and removed from under the tree.

7. The white bags were then deflated in about half an hour to lower the sequoia's root ball to the bottom of its hole. The bags were removed, but the metal bars were left with the tree because they rust and degrade over a number of years.

8. For the next five years the local park service will monitor and maintain the tree in its new home.