A battle of the sexes is happening in Canada's urban forests and the losers are those with allergies.
A study shows the dominance of male trees is making it worse for people who suffer from allergies.
The study found that because female trees tend to make more of a mess with flowers and fruit, cities and nurseries shy away from planting them. Therefore more male, pollen-producing trees usually exist.
"The female trees tend to make a little more mess in terms of seed production and fruit production so they would move to male trees because they aren’t making a mess," said Bill Roesel, the city forester in Windsor, Ont.
According to the study, 74-98 per cent of trees in Canada's urban forests are male, depending on the city.
"Female trees drop seeds and fruits while males are considered litter-free so they are favoured in urban planning," said horticulturist Thomas Leo Ogren, who was commissioned by the makers of Reactine to conduct the study.
In Windsor, Roesel, opts for monoecious trees, ones that produce equal amounts of male pollen and female flowers and fruit.
He usually opts for maple or oak trees.
Roesel said the city used to have more male than female trees. Most of them ash, but when the emerald ash borer arrived it killed off the trees.
Roesel admitted the city refuses to buy ginkgo biloba trees because the "female fruit is rancid."
And the city no longer plants poplars because they produce so much pollen and make such a mess.
Ogren recommends that city planners add the allergy potential of a tree to their list of considerations when selecting new trees to plant.
He also said gardeners and allergy sufferers can help themselves by recognizing the sex of a neighbour's tree. If a neighbour has a male tree, plant a female one.
Roesel said determining a tree's sex isn't that easy.
"A lot of time you can’t really tell for the first little while," he said. "Trees have to be fairly mature before they begin producing pollen or flowers."