California's Urban Forests At-Risk

Jul 07, 2015, 11:00 ET from Dudek

SAN DIEGO, July 7, 2015 /PRNewswire/ -- The 177 million trees in California's urban forests are at-risk as state-mandated water cuts start to significantly reduce irrigation vital to mostly non-native, ornamental trees, according to two long-time native habitat experts.  For context of the threat, 12 million native trees in California's wildlands have died due to the extended drought.

The warning about the state's urban forests came from Michael Huff, a professional urban forester/fire protection planner, and Michael Sweesy, a licensed landscape architect specializing  in California native habitat design.  Both are consultants with Dudek, a California-based environmental firm.

A recent U.S. Forest Service report estimated that just 5% of the state's entire urban forest, the 9.1 million municipally-owned street trees, provide an estimated $1 billion annually in beneficial services and have a $2.5 billion replacement value.  Urban forests range from the City of Los Angeles' 10 million trees to the City of Pasadena's 228,000 trees.

Weakened urban forests can reduce trees' benefits, including capturing pollutants, reducing heat and noise, capturing stormwater runoff, and creating the visual appeal central to local community character. 

These forests are already under attack.

Drought-stressed trees are more vulnerable to pests such as the polyphagous shot hole borer, which is killing trees via fungal infection throughout Southern California.

Turf removal projects put adjacent trees at risk if the typical spray sprinklers are turned off instead of replaced with drip irrigation. 

Most significantly, the fire threat will increase at the wildland–urban interface. If not properly thinned, dead and drought-stressed trees and vegetation (understory plants that can serve as fuel ladders) would provide pre-dried fuel—"ember catchers"—to facilitate the spread of wildland-initiated fires deeper into populated areas, especially during low humidity and high-wind events.  

Proactively managing fire protection in wildlands versus urban forests has one key difference: centralized public ownership versus fragmented private ownership of 80% of California's urban forest.

Public forests benefit from agency oversight and public funding.  The federal Healthy Forest Initiative and Healthy Forest Restoration Act, for example, helped remove barriers to and fund removal of dead trees in state and national forests, on tribal land, and on some private land.

Private trees do not typically receive the oversight and maintenance that municipalities provide. Fragmented private ownership represents a significant hurdle for coordinating plans and implementing solutions. A private property owner facing the expense to remove one or multiple dead trees may not weigh the risk-benefit of leaving dead vegetation in place.

"Our municipal and commercial clients accept tough choices for  effectively managing an urban forest, which includes removing even healthy non-natives that have no place in semi-arid Southern California," Huff said.  "Those decisions can be harder for homeowners who have emotional or financial reasons to keep their trees.

Mark Forster

Available Topic Expert(s): For information on the listed expert(s), click appropriate link.

Mike Huff

Mike Sweesy