Magnolias or Palms? One City Weighs Eco-Benefits of Its Urban Forest

Why is there a plan in San Diego to rip out 107 shade trees, when most of the valuable services they provide will be lost?

Magnolia trees on Broadway, a busy street in downtown San Diego/Credit: Robert Krier, InsideClimate News

Rip out mature shade trees and put in palms?

That's the debate going on now in sunny San Diego—and it is shedding light on the complexities of a resource that has long been taken for granted but is increasingly recognized for its value: the urban forest.

It all started when some groups proposed removing 107 magnolia and ficus trees on Broadway, a busy downtown street. The idea was to replace them with medjool date palms, which already line the city's nearby waterfront.

To some people, the idea makes about as much sense as ripping out your front teeth and replacing them with tooth picks. They view the trade as an environmental misstep, because a palm provides comparatively few environmental benefits and absorbs only about half as much carbon as a similarly sized magnolia. And they say the idea is driven by an outdated notion of Southern California's identity.

Others love the concept and say it will beautify and unify an important thoroughfare and visually tie it with the waterfront, a major tourist attraction.

If anyone can pin a value on a particular tree, it would probably be Kelaine Vargas, founder of a San Francisco-based company called Urban Ecos.

"Trees provide us with ecosystem services," she said. "They do work that goes beyond sitting out there in the landscape and looking pretty."

Vargas is trying to help cities recognize what trees can do for them. She developed a software program with the U.S. Forest Service to help municipalities map their trees, both public and private, and quantify their myriad benefits.

The maps, which have been created for Sacramento, Philadelphia, San Francisco and San Diego, keep a running tally of the trees' monetary contributions. San Francisco's "yearly eco-benefit" from its 86,815 mapped trees, for example, is $3,446,292.

The calculation, based on each tree's species, GPS coordinates and trunk diameter, shows San Francisco's trees are taking in 26,947,681 pounds of carbon from the atmosphere, a contribution worth $538,953; saving 139,655,264 gallons of water, worth $558,621; conserving 13,554,893 kilowatts of energy, worth $1,179,312; and reducing 94,027 pounds of pollutants from the atmosphere, valued at $555,405. (Last week's Weather Insider column focused on a recent recalculation of trees' ability to sequester carbon.)

Trees' "eco-benefits" are a big part of the debate in San Diego, a much larger and more geographically diverse city than San Francisco.

According to Mike Palat, an arborist and chairman of the San Diego Regional Urban Forests Council, shade trees not only sequester far more carbon than palms, they also produce much more oxygen, capture more storm-water runoff and air pollutants, and provide more shade to cool an urban area loaded with asphalt and concrete.

"It is truly night and day, the environmental benefits from a mature shade tree compared to a palm tree," Palat said. "Plus, the palms are higher maintenance" because date trees can be very messy.

"The existing trees are in good health and provide benefits. If you have to tear out trees, at least have a good reason to do so."

The dispute in San Diego was triggered by an effort that has other environmental implications: a push to make rapid transit downtown more accessible and appealing. A regional planning agency, known as SANDAG, plans to put eight new bus stations along Broadway. Doing that will require reconstructing sidewalks and medians and removing about 25 magnolia trees.

SANDAG, which has $1.5 million in taxpayer funds for the trees, held meetings with downtown business and property owners to discuss the proposal. That's where someone came up with the idea to replace all the trees on Broadway with palms. Janelle Riella is director of policy for the Downtown San Diego Partnership, one of the groups that wants the palms installed. Riella didn't return calls for this story, but she told KPBS, a local public radio station, that the palms would link the street with the North Embarcadero waterfront.

"If you bring that all the way through Broadway, it could be really beautiful," she told the station.

Vicki Estrada, a land planner who wrote the current landscape manual for downtown San Diego, said she recognizes that the business group was trying to make the environment as pleasant as possible.

"But they didn't realize what it does to the character and usability of the streets," she said. "If you ask 100 people, would you rather sit under a broad shade tree or a palm tree, they'd all say a shade tree.

"This is done mostly for tourists, at the expense of those of us who live and work downtown."

Estrada said the medjool palms may conform to a tourist's notion of Southern California, but they're desert plants and don't belong near coastal moisture. Botanically, the palm isn't even a tree, as some arborists always point out. It is in a family called Arecaceae and similar to grasses. Neither the existing trees nor the palms are native to San Diego.

Many cities, including Los Angeles and Miami, have stopped using palms for landscaping because of the mess, expense and, as the arborists say, lack of environmental benefits. In fact, most arborists have an almost visceral reaction against palms.

But Vargas, who helped launch the tree-mapping project for San Diego and other cities, said she's a contrarian among arborists.

"It's not so easy to say 'Shade trees have all these positive qualities, and palm trees have none,' " said Vargas, who lives in San Francisco. "Palm trees have their own value that's not insignificant."

She said the palms' aesthetics, although a matter of personal opinion, shouldn't be completely dismissed. And she points out that the roots of magnolia and ficus trees can ruin sidewalks, causing their own maintenance problems. Sometimes, shade trees also keep a residence or a business cooler than the owner wants.

At the moment, it's not clear how San Diego will resolve its downtown tree dilemma. A SANDAG spokesman said work on the new bus stations is scheduled to begin in January and the agency will plant whichever tree varieties the community agrees on. If palms are the choice, though, someone will have to come up with money to care for them, since palms would cost more to maintain than the existing trees.

To Vargas, the palm/magnolia debate is an encouraging sign that more people are becoming aware of the role of the urban forest.

Among those who have weighed in on the discussion are students at a small, private elementary school - Renaissance Village Academy in nearby Scripps Ranch—who wrote letters to SANDAG to protest the plan.

"The students were very unhappy that they were spending money the city doesn't have to take out perfectly good trees and put in palms," said their teacher, Samantha Fontana.


 Tropical and Tornado Activity

The hurricane season is off to an early start in both the Atlantic and eastern Pacific, but that doesn't necessarily mean the year will be active.

The National Hurricane Center issued its seasonal forecast last week. It says there's a 50 percent chance of a near-normal season, and a 25 percent chance of either an above-normal or below-normal season.

The center says there's a 70 percent chance of nine to 15 named storms, four to eight hurricanes, and one to three major hurricanes. The predictions are similar to hurricane forecasts last month from climatologists at the University of Colorado at Boulder and the private forecasting company AccuWeather.

The hurricane season in the Atlantic officially begins June 1, but tropical storm Alberto formed off the South Carolina coast on May 19. It had little impact on the Atlantic coast. Tropical storm Beryl, which veered into the Atlantic from the coast of North Carolina Wednesday, was another story. It made landfall in northern Florida on Sunday with winds near 70 mph, and it dumped copious rain on the southeast.

Beryl's development into a tropical storm on May 25 marked the first time since 1908 that two Atlantic storms have formed so early.

In the eastern Pacific, tropical storm Bud formed on May 22—the earliest date ever by a week—for the second tropical storm of that season. Bud later developed into a Category 2 hurricane, with sustained winds over 110 miles. It weakened back to a tropical storm before drenching the Mexican coast near the port city of Manzanillo.

May, usually the most active month for tornadoes in the Midwest, has been relatively quiet. Preliminary reports, which are usually lowered after they are investigated because of duplication, show only 122 tornadoes through May 26. Last year, there were 326 confirmed twisters during the month. The quiet May comes after an exceptionally active March and April, when preliminary reports showed more than 450 tornadoes and 11 deaths. No tornado deaths have been recorded in May.


Heat Happens—Again

The Memorial Day weekend brought record heat to Kansas and Nebraska, as well Indiana and Illinois. Phillipsburg, Kan., hit 103 degrees Saturday. Several other spots in the state and in Nebraska had their earliest-ever 100-degree readings.

An all-time May record of 97 was set in South Bend, Ind., on Sunday. Chicago had its hottest day ever this early in year with a high of 97, and Rockford, Ill., hit 99. The heat follows the the third warmest April and the warmest March ever recorded in the continental U.S. 

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