Even drought-tolerant trees die in San Diego Is water conservation backfiring?

Torrey Pines State Reserve

San Diego needs many more trees and must take better care of the sparse trees it has.

Trees shade us from the sun, reduce urban heat and noise, save energy, raise property values, improve air and water quality, mitigate climate-change effects, and create wildlife habitats, among many positive benefits.

The city seriously lags in the planting and maintenance of trees. It has a tree canopy — the layer of leaves, branches, and stems that cover the ground, as seen from the air — that is remarkably low for an American city. Tree San Diego, a nonprofit set up in 2014, says the local tree canopy is 60 to 70 percent below what it should be for the health of humans and the environment.

Source: October 2016 San Diego Tree Canopy Assessment

What’s the problem? San Diego has a Mediterranean climate featuring long periods without moisture. Even drought-tolerant trees can die, and trees are more susceptible to disease when they get little water. Political correctness gets part of the blame. Says Anne Fege, chair of the City of San Diego Community Forest Advisory Board, “During this drought, businesses and government agencies have turned off irrigation systems to get credit for ‘gallons saved,’ so trees have died across the region. Even the strictest drought restrictions allow for watering trees.”

Other big problems are indifference and neglect. Between 1985 and 2002, San Diego area tree cover dropped 29 percent while the urban area expanded 41 percent, according to a study by American Forests. In the past decade, San Diego’s tree health and canopy cover have declined sharply, says Fege. Among the causes were “deferred maintenance” and “a constrained municipal budget,” she says. Few local politicians realize the importance of street and park trees.

“At the low point in about 2010, the city had three tree trimmers, a park arborist, a forester in the undergrounding utilities’ capital improvement program, but no city forester or arborist for street trees,” says Fege. Later, the staff was increased by two positions, but according to a 2012 report by the Society of American Foresters, 12 large U.S. cities had an average urban forestry staff of 39, ranging from 7 to 171.

Fege warns that San Diego’s comparatively small staff “clearly is insufficient” for the city’s forestry program. Community leaders, business, and the public must push to get the budgets to acceptable levels. At one point, San Diego city councilmembers recommended funding the planting of 2000 trees in fiscal 2017, along with restoring some staff positions and removing tree planting from the lowly “amenity” status. However, the tree planting was not funded.

“I think trees and the urban tree canopy have been a low priority for all our local governments, especially during the Great Recession,” says Bill Tippets, retired supervisor of the state’s Habitat Conservation Programs for Southern California. Trees and the urban canopy “are likely to stay as a foster child in city functions until the value of the urban tree canopy assessment is accepted by and integrated into the City of San Diego’s — and the region’s — climate action plans.”

According to an urban tree canopy assessment completed this summer, the San Diego urban tree canopy covers an unimpressive 13 percent of the land area. “The 13 percent canopy is low,” says Jarlath O’Neil-Dunne, head of the spatial analysis laboratory at the University of Vermont and quarterback of the San Diego assessment. “New York City has 21 percent and San Jose has 15 percent.” He does take climate differences into account. Also, he warns, “With no or limited arborists, [San Diego] will have difficulty not only maintaining the tree canopy it has but dealing with dangerous or hazardous trees. Trees are an important part of the green infrastructure, and not maintaining them will cost the city more in the long run.”

According to the urban canopy assessment, 21 percent of the San Diego urban area is not suitable for trees, but 66 percent is potentially available for planting trees. The University of Vermont study shows that Solana Beach, Del Mar, and Encinitas are the only cities in the county with an urban canopy of more than 20 percent.

Source: October 2016 San Diego Tree Canopy Assessment

“San Diego has few native trees,” says Fege, as chaparral and coastal sage habitats dominate native vegetation. However, “coast live oaks grow throughout the county.” They are slow-growing and commonly planted in urban areas. Cottonwood, willow, and sycamore trees grow along rivers and creeks, but they require extra irrigation and space when planted as street, park, or residential trees.

“For me, the Torrey pine is a good tree for coastal areas, where it is naturally found,” says Derek Langsford, biology practices manager at Escondido’s Tierra Data, Inc. “It may be the most ideally suited tree for our region that doesn’t need a lot of supplemental resources — water, fertilizer — to do well.” (The Torrey pine is a rare species that grows naturally only in the Torrey Pines State Natural Reserve and one of the Channel Islands, but people grow them from seeds and plant them elsewhere.)

San Diego’s Mediterranean climate (dry summers and wet winters) is ideal for trees native to Australia, South Africa, Chile, Spain, and Italy. However, many kinds of trees have been planted in the county with “mixed success,” says Fege.

An example is the massive planting of eucalyptus trees shortly after the year 1900. According to a 1970 article in the Journal of San Diego History, the Santa Fe Railway (short for the renowned Atchison, Topeka & Santa Fe) decided it wanted eucalyptus trees to be used as railroad ties. In 1906 it bought the property now known as Rancho Santa Fe and planted three million eucalyptus trees on 8800 acres. Others in San Diego County followed suit. But 20 to 30 years earlier, the Southern Pacific Railroad had experimented with 44,000 such trees and found the poles rotted excessively and the ties cracked and wouldn’t hold spikes. The railroad ditched the experiment. The Santa Fe system apparently had not done its homework. Or maybe the Southern Pacific kept its expensive flop a secret.