To ensure adequate stability and to allow a tree to grow to its potential size, a tree’s root system must have adequate soil volume in which to develop. There is a direct relationship between soil volume and crown volume. When soil volume for root growth is reduced, tree size is usually smaller. Tree roots generally extend outward one and one half to two times the tree’s height (Gilman 1997).
Because engineers need compacted soil to place sidewalks, streets, and buildings, tree root growth is usually confined in urban environments. Several design methods are available to increase soil volume. These include the use of specialized cells that provide the needed structural support for sidewalks and roads, while providing the needed soil volume and pore space required for proper tree growth.
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Gilman, E.F. 1997. Trees for urban and suburban landscapes. Albany, NY: Delmar Publishers. 662 p.
By: Ed Macie, Regional Urban Forester, USFS Southern Region