A tree-lined avenue in Patiala, Punjab. Photo: Dollar Gill/Unsplash
- Is there any truth to viral TikTok and Twitter claims that cities have made allergies worse by planting mostly male trees?
- The answer is complicated, but it is notable that most trees in the world are not dioecious – i.e. they don’t have distinct male and female individuals.
- The main culprit is most likely climate change, which triggers plants to release more pollen during longer allergy seasons.
Over the summer, a video by a woman named Ellie Botoman appeared in my TikTok feed. In it, Botoman used a popular sound from a mid-2000s Nike commercial of LeBron James saying, “Oh, lord.” TikTokkers often use it to tell stories of revelation, and in Botoman’s video, it plays while she sips a mug in her well-appointed apartment. The text above her reads: “When you realise that allergies/asthma across north america got worse [because] landscapers + city planners thought male trees were easier to maintain.” The climax of the video is Botoman sharing this realisation: “You’re sneezing and congested all day [because] of botanical sexism.”
Soon after, crop scientist Sarah Taber wrote a Twitter thread breaking down why the botanical sexism theory is bunk. That also went viral. “This ‘male trees are a capitalist scam’ idea worked its way to TikTok from a hustler named Tim Ogren,” she wrote in the thread’s introduction. (Ogren’s first name is actually Thomas, and he often goes by Tom.) “Spreading this disinfo around is just doing free advertising for him.” Taber’s identification of Ogren as the center of the theory led me to go back and review news stories from the past decade and a half about the phenomenon; every single one I found either includes Ogren as the primary source or quotes from his op-eds in Scientific American or the New York Times.
Botoman’s TikTok was just the most recent viral propagation of the concept – it received more than 26,000 shares and 465,000 likes. Users riffed on the idea in the comments: “Patreearchy,” one wrote. “MEN LITERALLY RUIN EVERYTHING,” wrote another. Others threw out companion theories they thought further explained the phenomenon: “female trees produce fruit and capitalists don’t want us eating for free,” one wrote. And as fall allergies set in, it appears the idea is making the rounds again.
But the idea of botanical sexism has been around since at least the midaughts, cyclically appearing each spring or summer alongside allergy season. “Male plants have been popular because they don’t produce messy fruit or seed pods – but they are responsible for most of the pollen in the air,” an NPR reporter wrote in a 2006 article that, naturally, quoted Ogren.
Botanical sexism is one of those tantalising ideas that claims that something we see every day – the trees in our literal backyards! – might have a much deeper story, if only we looked closer. Equally intriguing is the idea that Ogren, as the creator of this concept, might be some kind of hustler, as Taber claims: Who doesn’t love a good old-fashioned grift? (And in particular: Has any other grift involved tree pollen, of all things?) But how much can we really blame “botanical sexism” for our allergies? The answer is, predictably, more complicated than any pithy TikTok or tweet thread can adequately convey.
First, let’s break down the main claims of botanical sexism. Mainstream explanations of the theory – such as Botoman’s TikTok – focus on an overabundance of male trees as the root cause of this issue. In that 2006 NPR piece on the idea, Robert Siegel parrots this talking point: “The reason that there’s so much pollen in the air is that there are so many male as opposed to female trees and plants around. Is that right?” he asks Ogren, who replies: “That’s right, Robert. In urban landscapes, there’s virtually no sexual diversity. There’s a big preponderance of male trees and shrubs and a scarcity of females.”
When discussing this supposed overproliferation of “male” trees, Ogren and reporters often include one detail as evidence for the theory: that the 1949 USDA Yearbook of Agriculture – the government itself! – recommended planting male trees only. “This advice was given to readers: ‘When used for street plantings, only male trees should be selected, to avoid the nuisance from the seed,’ ” Ogden wrote in a 2015 Scientific American op-ed.
Later in that piece, Ogren says that to stop what he calls the “allergy epidemic,” he recommends planting female trees, which “trap and remove large amounts of pollen from the air.” Local communities could also take up pollen ordinances and avoid planting pollen-heavy trees; to determine pollenicity, he offers up OPALS, a pollen-rating scale he created in 2000.
In her debunking thread, Taber calls Ogren a hustler in the very first tweet. “Spreading this disinfo around is just doing free advertising for him,” she says. She takes issue with a key tenet of the botanical sexism idea: “There are no ‘male vs. female trees’ for most species. It is impossible to plant only male trees,” she writes. This is true; while some trees are dioecious, meaning there are distinct male and female individuals, the vast majority are not. A forester at the University of Georgia School of Forestry estimated that globally, only about 5% of trees are dioecious; the rest are monoecious, cosexual or polygamous, meaning a single tree can have both male and female reproductive organs.
Also, there’s no vast conspiracy to plant only male trees, Taber says. She sent me a link to the 1949 USDA Yearbook. Indeed, while Ogren’s telling paints the Department of Agriculture’s words as a broad recommendation for male trees in general, the passage is actually specifically about cottonwoods. The next sentence describes how those seeds clog sewers and drainpipes, and that, in general, cottonwoods have weak wood and one should avoid planting them on any streets, lest a strong storm take a tree down.
As for whether planting female trees could help, Taber is a hard no. “Pollen is so cheap that trees can afford to make extra. Like, a LOT of extra,” she writes. This is just how plants pollinate – they release a ton of pollen, hoping that at least some of it finds its way to the right place. The hopes of controlling pollen, or making it go away entirely, are “selling rich hypochondriacs a sense of control,” she told me. “It’s taking advantage of their fears.”
Taber’s and Ogren’s claims seem diametrically opposed, and each feels strongly that the other has got it wrong. (If you’ve ever seen the meme of two Spider-Mans pointing at each other, that’s how I felt after talking to both of them.) To get an outside view on all this, I spoke with Rita Sousa Silva, an urban ecologist at the University of Quebec at Montréal who has studied tree pollen allergenicity, and she highlighted some nuances missing from both Ogren’s core theory and Taber’s thread.
First, let’s consider the claim that male trees are more prevalent than female trees in the urban landscape. Unfortunately there is very little solid data on this, and what I was able to find actually originates with Ogren, who was paid to do an allergy assessment of several Canadian cities. At the time, there were some local media stories about it; for instance, Vancouver’s city planner says that 30% of the trees planted by the city were male cultivars. Still, that only includes city-planted trees; individual homeowners plant trees, too, and many trees predate modern cities.
Also read: Dear Forest Department – Where Are the Native Species in Delhi’s Urban Forests?
What Taber claims is true, says Sousa Silva – but the trees that are planted in urban areas are a small sub-sample of what exists in nature, so there is a chance that there are more male trees in cities. Even dioecious trees can be cultivated to lack “female” qualities, like dropping messy seeds and inedible fruit. Both planners and homeowners might have preferences for trees based on these qualities, but that doesn’t make it sexism. “You choose maple trees because you want red leaves in winter, or you choose fruit trees because you want berries or apples, not because you’re picking a female or male tree,” she says.
Sousa Silva also takes the middle road on whether tree selection could affect allergies. “In theory, [female trees] would at least remove part of the pollen in the air,” says Sousa Silva, but, as Taber pointed out, wind-pollinated trees release large amounts of pollen, and there’s no getting around that. Is the solution, then, planting “low allergenicity” plants, à la Ogren’s OPALS scale? A greater diversity of plants can help, Sousa Silva says, but she expressed some reservations about the OPALS scale.
When trying to use the scale in her own work, Sousa Silva was struck by its opaque rating system, which she says has “no scientific background” – there is no internally consistent system to weigh the various factors Ogren says he incorporates. For some plants she knows well, she disagrees with Ogren’s OPALS ratings. To truly determine allergenicity, she would want to have more data about the local environment: How prevalent is the plant, and are the people in its direct vicinity actually allergic to it?
Unfortunately, that information is also hard to come by. Generating detailed data about urban plantscapes is a huge undertaking for any community, and different people are, of course, allergic to different things. And even these individual tests for allergenicity can be flawed. Generally, allergy testing relies on skin pricks; a person is poked with an extract from a potential allergen, and if their skin develops a reaction, they are considered allergic. But because medical companies only manufacture certain samples for tests, a person living in the U.S. being tested for, say, a birch tree allergy, will likely be tested using an extract from Sweden, because that’s where samples were developed, says Sousa Silva. That sample might be quite different from the birch in your yard.
Ogden is not wrong that seasonal allergies seem to be worsening. The main culprit, though, is most likely climate change, which triggers plants to release more pollen during longer allergy seasons. And while planting more female cultivars might reduce the overall amount of pollen in the air, it’s not exactly practical to cut down every male cultivar and replace it with a female. Rather, says Sousa Silva, we could focus on planting a variety of trees, especially those that are insect-pollinated, as they release much less pollen than trees that rely on wind pollination. That will take urban ecologists, public health experts, allergists, and other experts putting their heads together. “You need a team with different expertise,” she says. “There’s no silver bullet.”
Perhaps if we are more thoughtful about what trees we plant, we can avoid making allergy season even worse. And in fact, for years, Ogren was giving interviews about this idea without calling it botanical sexism. And his use of the term has evolved over time. The earliest mention of the term I could find was in a Globe and Mail article from 2011, in which Ogren apparently says people should practice “botanical sexism” by choosing only female plants to avoid allergies. In the mid-2010s, though, it seems that Ogren and those covering his work had pivoted to use the phrase to refer to bias against “female” plants instead.
I was fascinated by this pivot; it seems like the evocative moniker for the phenomenon in no small part drives its popularity. I asked Ogren about the term, and whether he feels that it represents sexism. He tells me a story about his wife – that years ago, when they first got married, she had terrible allergies, and Ogren read a book about psychosomatic illness and became convinced that his wife needed to just buck up and get over it. Eventually, while teaching in a prison, he discovered that even “tough guys” had allergies and discovered the error of his ways.
“When I was young, there was so much more sexism,” he says. “I believed that book on psychosomatic symptoms. The whole attitude about the thing was sexist.” And so when he discovered this potential imbalance of tree representation, it seems he was eager to call that sexist, too.
And that idea has clearly caught on. In this cultural moment, when sexism appears to be everywhere, and conspiracy theories about those in power run rampant, it’s no surprise the concept has some mass appeal. “If you’re under 45, your life already blows,” says Taber. “Everyone’s trying to make sense of why everything sucks, and this story about botanical sexism is perfect at tapping into that.”
Future Tense is a partnership of Slate, New America and Arizona State University that examines emerging technologies, public policy and society.