Energy & Environment

Allergic Tree Action

Cities' preference for planting male trees has led to the proliferation of pollen.
by | June 2006

If you just finished hacking, sneezing and wheezing your way through spring, you might consider filing a sexual discrimination suit. As it turns out, the field of urban horticulture is fraught with sexual politics and a history of concerted gender favoritism. And it just might be making you sick.

The gender bias here has to do with trees. Some of the most common types of trees used in urban landscaping, including many maple, ash, aspen, poplar, juniper and willow trees, are what's known as "dioecious." They're separate-sexed, meaning a poplar may be either male or female. For decades, the male trees have won the hearts of city planners because they're easier to maintain. They don't produce "litter," the seeds and fruit that fall to the ground from female trees. But the males do shed something that can be much more harmful to an urban population: pollen. After half a century of male-dominated plantings, cities are now filled mostly with allergen-producing trees.

It's arboreal misogyny, and it's got to stop, says Tom Ogren, an agriculturalist and author. Ogren is something of a guru when it comes to gender-based horticulture. Through speaking engagements and his books, including "Allergy-Free Gardening" and "Safe Sex in the Garden," Ogren advocates an approach to urban landscaping that prizes gender diversity in an effort to reduce pollen counts. Last month, the San Luis Obispo, California, writer returned from a 9,700-mile loop through the United States. "What I saw was an extremely pollen- intensive urban landscape," Ogren says. "You drive through these cities, and entire streets for miles and miles will be lined with the same trees. And they're always male, never female."

Ogren traces the modern proclivity for male trees to a 1949 U.S. Department of Agriculture yearbook called "Trees," which promoted planting male street trees because they're cleaner than female trees. The idea of low-maintenance landscaping grew in popularity for private homeowners, nursery suppliers and city planners alike. Favoring male trees isn't a bad idea in itself, and Ogren believes no one had any bad intentions. "But when a city does this on a massive scale, it has a huge impact on the health of the people who live there," he says.

Not everyone is convinced. Arborists and city planners argue that even if cities have become enclaves of horticultural masculinity, they're not the cause of your runny nose. Pollen blows everywhere, they argue, so diversifying trees in a city wouldn't reduce pollen counts significantly. Ogren concedes that pollen does travel up to 500 miles. "But the concentration of it is minuscule compared to the levels at the source."

If Ogren is right, it might not be very hard for cities to adapt to allergy-free landscaping. A handful of cities, all in the West, have already taken steps to curb pollen. Albuquerque, Tucson, Phoenix, Las Vegas, El Paso and a few smaller localities have adopted ordinances banning certain pollen-producing trees, including specific genders. But no East Coast cities have followed suit.

That could be why Boston recently found itself ranked among the worst American cities for pollen, in a report from the Asthma and Allergy Foundation of America (Hartford, Connecticut, and Greenville, South Carolina, topped the list). But while Boston does not have a ban on male trees, planners there do try to take allergies into consideration. "We definitely are trying to reduce allergy-producing trees where we can," says Leif Fixen, an urban forester with the city of Boston. Fixen says he's not familiar with Ogren, but he understands the argument. "We don't have anything on the books saying we can use only male trees, but in certain species, we will focus on one gender."

Ogren estimates the life cycle of an urban tree averages seven years, so a city that wanted to switch to female trees could do it relatively quickly. Of course, it might have to consider hiring municipal fruit-pickers. But Ogren's point is that cities do have some control over their pollen counts. "People tend to treat pollen as something like the weather. They say, 'Oh, it's awful, but there's nothing you can do about it.' But the truth is, that's not the case."

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