E. Gregory McPherson
USDA Forest Service, Pacific Southwest Research Station
Threats to tree longevity include increased heat and sustained drought, use of saline reclaimed water and/or periodic inundation, stronger winds associated with extreme weather, and new alien pest outbreaks. A community could experience large numbers of tree failures that are not only costly to remediate but exacerbate power outages, traffic congestion, and loss of benefits from mature trees.
Selecting species with internal genetic traits that promote resilience to external threats reduces the vulnerability of the future urban forest. Because threats vary regionally, local expertise may be needed to identify and prioritize threats for different tree species.
For example, red oak (Quercus rubra) grows natively from Georgia to Nova Scotia, Canada. Because of its high-branching habit, rapid growth, and open shade, it’s commonly planted in Central Valley, Calif., parks and along streets. But it needs fertile soil and plenty of water.
Texas red oak (Quercus buckleyi) is a more climate-ready choice. This drought-tolerant West Texas native grows 30 feet to 40 feet tall and wide with an upright crown that becomes rounded with age. Like its cousin, leaves turn burgundy to brilliant scarlet in the fall. It also establishes excellent structure with well-developed leaders and strong branch attachments that require virtually no pruning.
“Why shade streets? The unexpected benefit” from the Center for Urban Forest Research.
McPherson’s "Effects of Street Tree Shade on Asphalt Concrete Pavement Performance"