Center Streetscape Trees and Tree Planting Systems

Trees By the Numbers

We're planting 45% more trees than we're removing!
Removing: 60 trees that are unhealthy, too large, or not suited to the area they are in
Planting: 87 new trees that will be the optimal type and size for the area

Types of Trees We're Planting

• Serviceberry (Amelanchier Canadensis)
• Emerald Avenue Hornbeam (Carpinus Betulus 'Emerald Avenue')
• Honey Locust (Gleditsia Triacanthos Inermis 'Skycole')
• Emerald City Tulip Tree (Liriodendron Tulipifera 'Emerald City')
• Japanese Zelkova (Zelkova Serrata 'Green Vase')
• Slender Japanese Zelkova (Zelkova Serrata 'Musa Shino')

See the full list of plants, including shrubs, grasses, ferns and perennials.

How We're Planting the Trees to Give Them a Better Environment

Current Tree Environment

Typical roadway and sidewalk construction relies on a well compacted gravel base to support the roadway and sidewalk and prevent settlement. This allows for a smooth and long lasting surface. That surface is also built to prevent water infiltration, as water under a road or sidewalk shortens its life.

Unfortunately this is not a nurturing environment to trees and resists proper root growth, which results in unhealthy trees. That is what exists throughout the streetscape today.

Silva Cells: A Better Foundation for Street Trees

Silva cells are a modular suspended soils system used to support a healthy growing environment for trees. The Silva Cells are installed under the sidewalk and are designed to essentially create a bridge that is filled with healthy growing media for the trees, while providing structural support for the sidewalk.

The Silva Cells are filled with a specially designed soil mix that promotes root growth.  The footprint of the Silva cells provides an extensive area for the roots to grow.

The addition of aeration piping and irrigation further promote a healthy growing environment for the roots.  This environment encourages root growth and encourages it in the location desired to prevent sidewalk damage from the roots as well.  Healthy roots result in healthy vibrant and long lasting street trees.

Construction of Silva Cells

Construction of the Silva Cells is a bit complicated as we need to excavate down several feet to allow for the installation of these Silva Cells.

Once excavated to the proper depth, the system gets built back up in layers: 

• It begins with a geotextile fabric being laid across the entire surface below the Silva cells. 
• That is followed by a layer of compacted gravel.
• Then the Silva Cell installation begins. The base goes in with opening left in areas that will be receiving trees. 
• The posts are then locked into the base and a geogrid is wrapped around the system and attached to the posts. 
• Strong backs are then installed to keep the posts in place during the filling of the Silva Cells and the remainder of the excavated area.These are filled in two soil lifts and the soil on the interior of the Silva Cells is gently compacted by foot. 
• The strong backs are then removed and the decks are attached. 
• A geotextile is then placed over the Silva Cells and covered with a compacted gravel base. 

At that point the Silva Cell installation is complete and the standard sidewalk construction can begin. This includes the concrete ‘mud slab’ base for the brick which is the finished surface.

Find out more about Silva Cells.

Complete List of Plants Being Planted