They may look pretty, but fronds hurt cities' sustainability efforts
Picture a line of gently swaying palm trees. Is there a greater signifier of a pleasantly warm climate and a great vacation spot?
But while palms are aesthetic superstars, a number of cities have started to recognize that the environmental issues fronds wreak can’t justify the eye candy.
When Florida's Miami-Dade County released its urban forestry master plan in 2007, the area’s iconic palms were noticeably missing from the list of approved trees. Instead, the county recommended everything from leafy Ebony Browns to spindly Desert Sennas. "While palms are aesthetically pleasing and look ‘tropical,’ they do not provide the same environmental benefits, walkable streets, or lower ambient temperatures as hardwood shade trees," the report stated.
And therein lies the crux of the problem. A recent study of three different tree groves in Tel Aviv, for example, showed that palms provide the least amount of shade and needed the most water, up to 1,000 liters per day. Ficus and Rosewood trees, meanwhile, have much lower water needs and managed to cool the surrounding area by seven degrees and three degrees, respectively. The palms chilled the air less than one degree.
A similar study on oases in southern Israel found that palms actually managed to warm the surrounding area.
“From a climatic point of view, it’s useless,” says Oded Potchter, a lecturer at Tel Aviv University. Potchter has tried to convince cities in Israel to stop using palms, to little avail. "They say it is nice and they will continue to use them," he says.
Stateside, though, it’s another story. Many palm-worshipping cities are seeing to it that the fronds no longer dominate the landscape in a bid to add shade and carbon-trapping to their tree cover.
"We are not using palms, but not because we don’t want to. We want to increase canopy coverage," says George Gonzalez, chief forester for the city of Los Angeles. "While palms are aesthetically nice, they don't add anything, so they are not on the list of 50 species of trees being used."
The public, though, isn’t always on board. When Santa Monica tried to do the same thing this summer, citizens showed up at a public meeting and forced a compromise. In the end, planners created designated palm alleys.
"The community really didn’t understand the environmental impact. They felt sunlight was also an asset," says Walt Warriner, the city’s community forester.
Most urban foresters point out that cities are still using palms in some places, and that they don’t want to change the overall feel of their city.
"The idea that we not planting palm trees in Miami is ridiculous. We have palm trees as part of our identity," says Christina Casado, community image manager for Miami-Dade County. But, she added, many of the city’s main thoroughfares now have broad leaves interspersed. And the county had amended its design specifications so developers can’t just use palms to meet tree requirements.
Global warming, which is most acutely felt in urban heat islands, has also played a role in urban foresters seeing the forest and the trees in recent years, according to a number of experts.
"We’ve covered most of our urban areas with asphalt or concrete. We’ve increased the heat island effect,” says Eric Corey Freed, a Palm Desert*, California, architect and author of Green Building and Remodeling for Dummies. Freed says that a number of cities have adopted measures, such as using more hardwood trees, to cool their cities.
"These low-tech means [to mitigate the heat island effect] are suddenly much more appealing," he says.
Photo courtesy of Flickr user AimeeWenske.
*Correction: An earlier version of this post said that Eric Corey Freed was from Palm City. He's from Palm Desert.