Planting Trees in Suspended Pavement

Lincoln Center's London Plane Trees, installed in a Silva Cell system in 2008, in summer 2013.  image: DeepRoot Green Infrastructure, LLC
Lincoln Center’s Barclay Capital Grove, installed in a Silva Cell system in 2008, in summer 2013.
image: DeepRoot Green Infrastructure, LLC

This article on suspended pavement, by Leda Marritz, ISA, of DeepRoot Green Infrastructure, is based on a comprehensive, multi-year literature search she conducted for the blog Green Infrastructure for Your Community. Green Infrastructure for Your Community addresses topics related to trees, soils, and stormwater in the built environment. Leda has written, edited, and run the blog, producing hundreds of articles in the past 4 years. I am very pleased to introduce Leda to write a blog post for The Field.
–L. Peter MacDonagh, FASLA, ISA, Director of Science & Design at the Kestrel Design Group and Adjunct Faculty, Practice Professor at the University of Minnesota’s College of Design

When we talk about low-impact development and design today, the term “suspended pavement” comes up a lot, but it occurred to me recently that this term is rarely defined. Here is my attempt to do that by walking through suspended pavement’s history, uses, composition, and case studies.

Suspended pavement (also known as cantilevered sidewalks) is a general term for any technology that supports the weight of paving and creates a subsurface void space that is filled with soil for root growth. The soil that is used to fill the system can either be native, from the excavation area itself (if appropriate), or a specified mix. In this respect, suspended pavements are essentially soil-delivery systems, creating a rooting area composed of lightly compacted, high-quality soils for tree roots in cities and other heavily paved environments. In addition to aiding urban tree growth, the soil can also be used for on-site stormwater management, maintaining pre-development hydrology, minimizing non-point source pollution and flooding, and recharging watersheds.

Suspended pavements are ideal low-impact development design solutions for the long term co-existence of trees and streets, parking lots/lanes, roofs, promenades, plazas, green walls, and light-rail platforms.

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