OTTAWA – There’s a biological war of the sexes raging in North America’s trees, and people with pollen allergies are the casualties.
A huge majority of the trees in many Canadian and U.S. cities are male.
Female trees are messy. They are the ones whose flowers go on to produce nuts, seed pods, apples and other seed-carrying debris that people don’t like to sweep up off decks and patios or scoop out of clogged eavestroughs.
So growers have switched to supplying male trees, which don’t produce seeds.
Instead, the male trees produce pollen. And that aggravates allergies.
Tom Ogren, a horticulturalist from California, came to Ottawa as part of a cross-Canada tour sponsored by the makers of Reactine allergy medicine.
The average male tree produces an amount of pollen equal in weight to the female tree’s seeds, he said. But the pollen is mostly invisible.
Ogren doesn’t have allergies, but his wife of 45 years does. Years ago this gave him the idea of searching for the most pollen-free plants for his own home, and eventually for other people as well. He writes books on the subject.
But a funny thing happened when he went out to shoot pictures of male and females samples of each species. Near his California home he had trouble find the females.
“I thought maybe my city was unusual,” he said in an interview. But the same weirdly skewed population showed up in city after city – anywhere that the trees had been purchased from growers instead of growing naturally. It doesn’t occur in rural areas or small towns.
Ogren calls it “botanical sexism,” and he said it contributes to needless suffering by anyone with allergies to tree pollens.
On Wednesday, he toured Ottawa to see what kinds of trees are in the capital’s parks, schoolyards, nurseries and streets.
In a word, they’re male. At least most of the time.
That goes for a huge variety of trees and shrubs – juniper, horse chestnut, katsura, yew, ginkgo, ash, oak, aspen, poplar, honey locust, Manitoba maple, mulberry, and on down the list.
In some cases growers have even found a way to produce “all-male” versions of a tree that’s naturally both male and female, he said.
The locust, for example, naturally produces male branches and female branches on the same tree. It doesn’t occur in nature in an all-male or all-female version. But growers have learned to cut off a male branch and clone it, producing new trees without female branches.
In terms of what to plant, go with more female trees for a healthier environment, he suggested. Not only do they not produce pollen, but they attract it and clean the air of the tiny particles, and even smaller particles of airborne soot from vehicles that cling to them.