Underground Soil Cells First in Pennsylvania

Pittsburgh, PA (July 16, 2009)- The street trees outside of the new August Wilson Center for African American Culture are among the first to benefit from underground soil cell technology. With a generous grant from the R.K. Mellon Foundation and support from the City of Pittsburgh, Friends of the Pittsburgh Urban Forest partnered with the August Wilson Center and Terra Design Studios to develop a tree planting model that improves the longevity of the City of Pittsburgh’s urban street tree population.


“Trees are a critical element for a livable urban environment,” says FPUF Executive Director, Danielle Crumrine. Publicly owned trees – and, collectively our urban forest, provide a wide range of environmental, economic, health, and social benefits as essential to the vitality of a city as any other component of community infrastructure. Like streets, sidewalks, public buildings, and recreational facilities, trees are a major capital asset.
Unfortunately, trees must endure the harsh urban environment which results in an average lifespan of seven years. As a result, many trees die before they are able to grow large enough to shade a city sidewalk. Ultimately, the trees are replaced at a cost to city budgets or not replaced at all.
Some survive but never reach their full height or canopy, prohibiting them from offering their true environmental, financial and social benefits to their communities. The main culprit for urban tree mortality and stunted growth is the lack of non-compacted soil, which the roots need to access water, nutrients and air.
The underground soil cell system used for ten trees along Liberty Avenue is called Silva Cell. It is comprised of open stacks of plastic “cells” that are sturdy enough to support a sidewalk above while housing non-compacted soil in the voids below. The roots grow freely beneath the pavement, and as they have easy access to good soil, they are less likely to uplift and damage sidewalks. The cells also have the added benefit of providing additional storm water storage on site, which decreases the load on the City’s storm system. Silva Cell, through increasing available non-compacted soil volumes, mitigates the age-old conflict between roots and pavement by creating a system that allows them to live harmoniously side by side.
“The City is committed to improving our urban forest with more than 2,500 new trees planted in the City since the Spring of 2008 and another 2,000 slated for the 2009 fall planting season,” said Mayor Luke Ravenstahl. “The use of the Silva Cells is just one more example of how Pittsburgh is leading the way in adopting new technologies to become a greener city.”
“The August Wilson Center is thrilled to be a part of something that promises to improve the urban landscape of Downtown Pittsburgh, which has undergone a great transformation over the years. With this system, we are confident our 10 trees will be as fruitful as they were intended to be and encouraged that they will blaze the trail for future projects,” said the Center’s Senior Vice President, Jeff Anderson.
“This demonstration project complements the City’s commitment to plant 20,000 street trees by 2012 through the TreeVitalize program,” says City of Pittsburgh Urban Forester, Lisa Ceoffe. Together, FPUF and the City Planning Department are working to raise the standards of how trees are planted, and two additional Silva Cell projects are slated to be installed Downtown in the coming months.
Related Resources:
Friends of the Pittsburgh Urban Forest
Urban Landscaping- Part II: Tree Stock