Later this year, workers reunifying Old Courthouse Square will plant dozens of new trees to replace the towering redwoods and others that were felled at the beginning of the project in downtown Santa Rosa.

Whether the new sycamores and crepe myrtles thrive in their urban environment will depend largely on innovative underground preparations underway this week.
Workers began installing more than 1,000 black plastic structures that future visitors to the square will never see, but will directly affect how well the trees grow.
Called Silva Cells, the rectangular blocks, which look a bit like large hollow Legos, are designed to create subterranean spaces where tree roots can grow freely and storm water can collect before flowing into nearby Santa Rosa Creek.

Trees in urban environments often fail to thrive because they are planted in heavily compacted soil that prevents them from getting the air, water and nutrients they need, said Shawn Freedberg, an account manager with the San Francisco-based DeepRoot Green Infrastructure. Instead of growing downward and outward, tree roots often grow upward, resulting in pushed up sidewalks and pavement damage, he explained.