‘America’s Love of Male Trees Could Be Why You’re Sneezing Right Now’
‘Botanical sexism runs deep‘
‘More diversity in city trees would probably be a good thing’
One day in April 2019, the residents of Durham, North Carolina, saw the sky turn a peculiar but familiar shade of chartreuse. Enormous clouds of a fine, yellow-green powder engulfed the city. It looked, and felt, like the end of the world. “Your car was suddenly yellow, the sidewalk was yellow, the roof of your house was yellow,” says Kevin Lilley, assistant director of the city’s landscape services. Residents, quite fittingly, called it a “pollenpocalypse.”
Male trees are one of the most significant reasons why allergies have gotten so bad for citydwellers in recent decades. They’re indiscriminate, spewing their gametes in every direction. They can’t help it—it’s what evolution built them for. This is fine in the wild, where female trees trap pollen to fertilize their seeds. But urban forestry is dominated by male trees, so cities are coated in their pollen. Tom Ogren, horticulturalist and author of Allergy-Free Gardening: The Revolutionary Guide to Healthy Landscaping, was the first to link exacerbated allergies with urban planting policy, which he calls “botanical sexism.”
In trees, sex exists beyond the binary of female and male. Some, such as cedar, mulberry, and ash trees, are dioecious, meaning each plant is distinctly female or male. Others, such as oak, pine, and fig trees are monoecious, meaning they have male and female flowers on the same plant. It’s easy to identify female trees or parts—they’re the ones with seeds. And yet more, such as hazelnut and apple trees, produce “perfect” flowers that contain male and female parts within a single blossom. But while both monoecious and male dioecious trees produce pollen, Ogren claims the latter are primarily to blame for our sneezes and watery eyes.
Ogren has been talking about this botanical misogyny for over 30 years. After buying a house in San Luis Obispo with his wife, who suffers from allergies and asthma, Ogren wanted to get rid of anything on his property that might trigger an attack. He began examining the neighborhood, plant by plant, when he noticed something unusual: All the trees were male.
At first, he thought this pattern may just have been a strange quirk of one city. But when he studied frequently landscaped plants in other cities, he noticed the same thing: males, all the way down. “Right away I started realizing there was something weird going on,” he says. While tracking down the origin of this trend, Ogren stumbled upon perhaps the first trace of sexism in urban landscaping in a 1949 USDA Yearbook of Agriculture. The book advised: “When used for street plantings, only male trees should be selected, to avoid the nuisance from the seed.”
Urban forestry’s apparent sexism seems to boil down to our distaste for litter. The USDA reasoned that tiny allergenic spores are likely to be blown away by wind or washed away by rain, making pollen an easier civic task to manage than, say, overripe fruit or heavy seed pods that would need to be cleaned up by actual humans.
The preference indicated by the USDA recommendation is one element of the story—the other is something more tragic, from an arborial perspective. In the first half of the 20th century, lush, hermaphroditic, not-so-allergenic elm trees towered over many American streets. But in the 1960s, a virulent strain of Dutch elm disease, a fungal illness spread by the bark beetle, stowed away on a shipment of logs from Britain. The fungus wiped out some of American cities’ longest-lived trees and left many streets almost entirely devoid of green or shade. By 1989, an estimated 75 percent of North America’s 77 million elms were dead, according to The New York Times.
City planners and landscapers repopulated the nation’s barren, sun-scoured streets, according to USDA guidelines, with more than 100 new varieties of maple clones, Ogren says, all male. Over the years, male willow, poplar, ash, mulberry, aspen, and pepper trees joined them. As these trees matured, they shed increasing quantities of pollen. Nurseries began selling more male plants, too, in part because it is easier to clone an existing tree than to wait for males and females to pollinate each other naturally. Now, it’s not just trees and shrubs, but ornamental plants sold in urban nurseries that skew male. “Botanical sexism runs deep,” Ogren says.