"Often, cities plant new trees in a few cubic metres of poor-quality soil, with predictable results," writes author Wendy Stueck.
Although significantly more expensive, new technologies offer cities the option to improve the urban canopy by allowing large trees to thrive in urban environments: "Over time, working with American landscape architect James Urban, the company developed the Silva Cell, a system designed to help nurture big trees in urban environments based on research that shows larger trees provide exponentially greater benefits than smaller ones... Silva Cells are a modular system that puts tree roots under buried decks, with a layer of aggregate and pavement over top. The system provides drainage and irrigation and puts roots below the decks, so they don't push up and buckle pavement. It also ensures plentiful volumes of unpacked soil – about 15 to 20 cubic metres in a typical installation, compared with 1.5 to 3 cubic metres for a tree planted in a conventional pit."
Thanks to Brent Toderian