Are We Ready for ‘Hypoallergenic’ Parks?

Spanish researchers propose engineering parks and urban forests to take out allergy-causing trees.
Granada, Spain. (Photo: Patricia Hamilton/Getty Images )
Sep 4, 2015· 3 MIN READ
Richard Conniff is the author of House of Lost Worlds: Dinosaurs, Dynasties, and the Story of Life on Earth and other books.

Hypoallergenic parks: Coming soon?” That was the headline on the press release, and the specter of sanitized nature made me mutter, “Oh, crap.” So I downloaded the study. It’s being published in the Journal of Environmental Quality, and it made me wonder, for the first time in my life, whether we might be taking this whole damned environmental quality thing a bridge too far.

Let’s stipulate that we have already paved under much of the natural world to suit human needs, especially in and around cities, and further, that we often manipulate what’s left to our own purposes, and finally, that these changes almost always work to the detriment of the birds, butterflies, and other animals that once depended on these habitats. Is the logical conclusion that we now also need a war on trees that happen to cause hay fever?

The study, by a team of Spanish researchers, looked at trees in Granada, a city admired for its abundance of handsomely planted boulevards, parks, gardens, and other green spaces. But because of its Mediterranean climate and long growing season, Granada is also a hay fever hot spot, with almost 30 percent of residents saying they are allergic to pollen.

The researchers found that a third of the city’s trees rated high or very high for allergenicity—the potential to elicit allergic reactions. Ranking near the top of the list were oaks, olive trees, and the tall cypresses that have deep cultural roots in the city’s rich Arab past. The seasonal sneeze-inducing potential of different neighborhoods varied from “breathe easy” in Zaidín Park, where the last vestiges of greenery seem to consist mainly of grass, on up to “your head will explode” in Bosque de Gomérez, a forest on the outskirts of the city.

It sounded like a prescription for clear-cutting, possibly by an army of hay fever–suffering vigilantes sneezing loudly enough to drown out the roar of their chain saws. So I tried the study on a couple of U.S. specialists in urban forests to see what they thought. “As a sufferer of seasonal allergies to oak pollen,” Paige Warren of the University of Massachusetts wrote back, “I have to say I sympathize with the authors’ concern over allergens and human health.”

But there are trade-offs, she added, and navigating them means asking questions like “How much does reducing allergen exposure from tree pollen benefit human health relative to other kinds of allergens (like ragweed) and other air quality issues (like fine particulates and other pollution)?” It should also never be just about us. So how much does the mix of tree species in city plantings matter to biodiversity—those birds and butterflies?

Douglas W. Tallamy agreed. He’s a University of Delaware entomologist and the author of Bringing Nature Home: How You Can Sustain Wildlife With Native Plants. He also once published a list ranking U.S. woody plant species by their wildlife value, with oaks at the top because they provide habitat for 557 species of caterpillar, a favorite bird food.

“If you are going to rank trees for urban use (and I am all for that),” Tallamy emailed, “don’t just use one criterion: rank them for all of their ecosystem services. Oaks are best for biodiversity. They are best for carbon sequestration. They are best for watershed management. Do we really want to throw all of that out because they are allergenic for three weeks of the year?”

Tallamy also noticed something intriguing about the new study’s list of sneeze-inducing trees: Many of them are not native to the region. Chinese arborvitae comes, no surprise, from East Asia. The Port Orford cedar is native to Oregon and California.

Paloma Cariñanos, a botanist at the University of Granada and lead author of the study, noted that the list of nonnative problem trees also includes casuarina, eucalyptus, ginkgo, and ailanthus (all commonly planted in U.S. cities too). But she pointed out that the allergy season in Granada can run for six months, not three weeks, and is likely to become a bigger health issue worldwide because of the warming climate.

The study does not envision wholesale tree removal, she said. But if all trees along a road are of the same species, and it’s a problem species, “we propose to modify this design by replacing one of every three trees with a tree of another species.” That would preserve some of the existing habitat for wildlife and might even increase biodiversity by adding a different kind of habitat. The plan would also replace trees that die, using a database categorizing 7,000 species by their biological, morphological, ecological, landscaping, and allergenic characteristics.

That is, it’s a trade-off. The only problem with the study is that it doesn’t state this balance of considerations loudly enough. And that’s a problem, because hay fever sufferers caught up in their misery are liable to take away the wrong message. It’s also a case of a press release writer gone amok, this time from the American Society of Agronomy. The term “hypoallergenic parks” never turns up in Cariñanos’ study.

The bottom line is that we need to protect urban tree cover, which is declining at a rate of 4 million trees a year in the United States. The rage for “million tree” planting campaigns is not by itself the answer. We need scientists to think carefully about the mix of trees being planted and include wildlife prominently in their consideration of pros and cons.

Finally, if your community still thinks planting gingkoes, eucalyptus, and other introduced species is a smart idea, you need to step up and sneeze in the face of local officials. The birds and butterflies (and hay fever sufferers) are counting on you.