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Unusual demonstration project looks to promote the growth of urban trees

(Véronique LaCapra/St. Louis Public Radio)

Engineers, arborists, and landscape architects from across Missouri and southern Illinois gathered in St. Louis on Thursday for an unusual demonstration project.

Brightside St. Louis is installing “silvacells” outside its Demonstration Garden and Learning Center at the corner of Kingshighway and Vandeventer.

The goal is to promote the growth of urban trees.

Brightside executive director Mary Lou Green describes the silva cells as something like open-sided plastic shelving or crates.

They are buried just below the sidewalk, forming a porous support structure for tree roots.

“That prevents the soil in between there from compacting the roots,” Green said. “And so it allows the roots to actually grow out, and not grow up and buckle streets or curbs, things like that.”

Mark Gruber, an urban forester with the Missouri Department of Conservation, says a lot of people think tree roots grow down.

“They really don’t, they grow out, sometimes 2 to 3 times the height of the tree as a distance from the trunk,” Gruber said. “So a 50-foot tall tree could have roots 100 to 150 feet out from the trunk.”

Gruber says trees in a paved, urban environment often die in less than ten years. He says installing silva cells will help the trees grow and could increase their lifespan by decades.

The Brightside demonstration project also includes porous pavement that allows water to pass through it. Gruber says the pavement and silva cells together will help reduce storm water runoff.

Here's a video (albeit slightly promotional), produced by the makers of the silva cells, explaining how they work: