Phoenix, Arizona is best known for its cacti and asphalt, not its tree canopy, but one city employee is trying to change that.
Richard Adkins, a forestry supervisor for the city, is on a mission to bring tree coverage to one-quarter of the city by 2030. Right now, the tree coverage is less than half of Adkins target number.
Why bring lush tree cover to a city mostly known for its desert plants? With a new emphasis on walkable neighborhoods over sprawling subdivisions, and the looming threat of climate change that will raise the mercury further, Phoenix needs to create refuges from the burning heat.
Some (mostly older) districts have a reasonable tree cover of 17 percent shade, while others have a paltry seven or eight percent. Natives species like palo brea and mesquite will be planted in conjunction with varieties like the Chinese pistache, a deciduous tree with a dense crown and deep root system that won’t buckle sidewalks. As an aesthetic bonus, the pistache turns blood-red in the fall before dropping its leaves. Palms, a ubiquitous site along medians, will be avoided as they do not provide much shade.
One model for Adkins’s initiative is three-acre Civic Space Park. Completed in 2009, the downtown park boasts a variety of native and non-native trees, pervious pavers, a solar canopy, and a coffee shop. When the trees mature in five to six years, the park should have 70 percent shade cover.
And yet, Adkins told the Los Angeles Times, “there’s a lot of pushback – ‘You plant more trees, well, we’re going to have to use more water. That’s where it gets into species choice and water management. Even today, most people over-water everything. But is water a consideration? Of course? Do I feel we have ways of watering and harvesting rainfall with green infrastructure to help provide for our street trees? Absolutely. Do I think we need to give up trees for water? No.”
The trees don’t need to be natural to be functional, though. Steel trees and canopies can provide cover from the sun on densely developed downtown corridors.
In addition creating an online inventory of Phoenix’s 92,000 trees, Adkins has tagged trees across town with labels to explain their environmental value using a metric developed by the U.S. Forest Service to determine a tree’s carbon storage capacity, how much electricity it could save surrounding buildings, and how much runoff it reduces. Beyond the cost savings they afford, trees have an extra economic value: People tend to gather in shady spots, so if a commercial corridor has many trees, it’s likely to get more business, Adkins reasons.