As much as 90 percent of urban plants are male. That means more allergies
With asthma cases reaching epidemic levels in American cities, public health officials have been casting about for clues, pointing to everything from roaches to vaccines to overcleanliness as possible causes. Tom Ogren thinks the trouble lies in the trees.
For the past 16 years, the San Luis Obispo, California, horticulturist has been studying the science of pollen and allergies and has concluded that genetic manipulation of the urban landscape may have more to do with the asthma epidemic than any other factor.
As Ogren explains, many of the plant species we grow in urban areas are dioecious—that is, like humans, each individual plant is either female or male. Such species also thrive in the wild, but in natural settings you’ll find a general balance of male and female plants, Ogren says. This equilibrium lowers the amount of pollen in the air, because there are enough female plants to receive the male-produced pollen. But female plants have been largely eliminated from the cities and suburbs by landscapers who prefer the 'cleaner' male plants (no messy flower or fruit debris). As much as 90 to 95 percent of dioecious plants in the city are now male, Ogren says. As a result, pollen infests metropolitan air.
'Without these natural air scrubbers, we now have many elementary schools ringed with pollen-producing male shade trees and full of asthmatic children,' Ogren writes in Earth Island Journal (Spring 2001). Allergy problems have increased in recent years, he adds, and deaths from asthma continue to climb at alarming rates.
Ogren has compiled his research about connections between allergies and pollen into a book, Allergy-Free Gardening (Ten Speed Press, 2000). He also designed the Ogren Plant Allergy Scale (OPALS), a system for ranking the allergy-causing impact of different plant species. The USDA recently used OPALS to estimate the plant allergen levels in more than a dozen U.S. cities, including Oakland, New York, and Atlanta. Though the information is yet to be published, most of the cities ranged from 5.3 to 7.6 on a scale of 1 to 10, Ogren says. He hopes the urban allergen rankings will eventually help people decide where to live.
Already, at least five U.S. cities (all in the Southwest) have enacted pollen-control ordinances to protect allergy sufferers, but Ogren says citizens also need to: push city officials to ban the sale and planting of male trees and shrubs; train gardeners in the art of tree-grafting so they can alter the sex of their plants; and require plants to carry an allergy rating. It’s time to embrace 'the politics of pollen,' he says. 'How many more children need to die from asthma each year before we decide to put an end to these destructive landscape practices?'
Discuss pollen at the Nature forum in the Utne Salon: www.utne.com/salon.aspx