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Analysis: ABC 10 News recently declared that San Diego has a natural claim to fame: the city with more trees than any other in the nation.
The March 1 story highlighted a mapping website that allows San Diegans to upload information about local trees. It also provides estimates on how those trees reduce carbon and improve the region’s air quality, among other impacts.
The goal is to urge cities to emphasize greater awareness about the area’s tree population and its environmental benefits.
The claim quickly set off our fact-checking radar. Sure, San Diego has lots of trees but so do plenty of other cities. The claim presented a chance to learn more about how San Diego’s tree population compares with that of other cities.
We consulted several experts who have studied urban forests. None could vouch for San Diego’s status as the urban tree capital of the United States.
U.S. Forest Service researcher David Nowak has spent years calculating the number of trees across the nation. He said he’d never considered San Diego among the nation’s front-runners though he stopped short of any conclusions.
“I don’t think we can confirm which city has the most because we don’t have data from all cities,” he said.
By Nowak’s count, Atlanta boasts the nation’s largest urban tree population. In 1996, Nowak’s team used a complex projection model to determine that the southern city had about 9.4 million trees. In 2008, they traveled to Los Angeles and calculated roughly 6 million trees there.
Michael Palat, chairman of the San Diego Regional Urban Forests Council, was skeptical that San Diego could compete with those cities.
He said San Diego’s arid climate presents a challenge for the city’s tree population.
Most trees require watering to survive in their infancy and not many of San Diego’s trees sprout up on their own, said Palat, who supervises the San Diego region for West Coast Arborists, a company that inventories trees in cities in California, Arizona and Nevada. The company has not conducted a count in San Diego.
Palat and others we consulted weren’t aware of any formal, citywide tree counts in San Diego. They could only recall a July 2003 report that relied on high-resolution digital maps to determine which percentage of San Diego and some parts of San Diego County were covered with trees. That’s a different measure than the number of trees in the city.
The study, conducted by the U.S. Forest Service and the nonprofit American Forests, made some city-specific assessments. At the time, about 7 percent of San Diego was covered by trees.
By that measure, San Diego’s tree population is not too impressive.
A 2010 U.S. Forest Service report on the status of the nation’s urban forests found that up to 80 percent of urban areas in some of the nation’s counties are covered by tree canopies. Those with the largest percentage of tree cover tended to be in eastern states.
“We cannot, as a city, say that is true,” spokesman Bill Harris said. “It is not, by our calculation.”
The city does keep an inventory of roughly 250,000 trees along its streets and sidewalks, which includes more than 220,000 shade trees and 30,000 palms, but there’s no record of trees on private property.
We informed 10 News reporter Natasha Zouves of some of our findings and she emailed to say that Robin Rivet, the arborist who helped create the tree-mapping site, was the one who told her San Diego had more trees than other cities across the country.
Rivet, who serves on the city’s Community Forest Advisory Board, disputed that.
“We are actually one of the most underperforming cities (in terms of) trees in the nation,” Rivet said. “It couldn’t be further from the truth.”
Rivet later contacted 10 News, and the story was updated. It no longer kicks off with the claim that San Diego has the largest tree population in U.S.
Rivet and others on the Community Forest Advisory Board do hope to make the city more tree-friendly after years of cutbacks. The board has urged the city to reinvest in its urban forestry program and last month, the city accepted a $75,000 grant from the California Department of Forestry and Fire Protection to implement an urban forest management plan. That will involve getting input from the community, reviewing the tree-specific guidelines the city set out in its 2008 general plan and developing a schedule of actions, said Anne Fege, chair of the Community Forest Advisory Board.
The group hopes to work with a local university or outside group to tally the city’s tree population but Fege and Rivet were adamant that process won’t reveal San Diego has more trees than any other city in the nation.
The evidence was overwhelming: San Diego can’t claim to be the nation’s most tree-covered city, so the statement in the 10 News story is “false.”
If you disagree with our determination or analysis, please express your thoughts in the comments section of this blog post. Explain your reasoning.
Lisa Halverstadt is the newest reporter at Voice of San Diego. Know of something she should check out? You can contact her directly at email@example.com or 619.325.0528.
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