This theory has become increasingly popular; however, many experts say planting practices are definitely not to blame for your sniffles, sneezes, and watery eyes.
The headline touts an abundance of male plants in a landscape as being a primary cause of allergies. It goes viral. Everyone piles on. Even TikTok weighs in with a popular video claiming "botanical sexism" is partially to blame for each year's worsening allergy season.
But did decades of a botanical bias really make a major contribution to your allergy anguish? Not exactly.
What is a pollenpocalypse?
That is the name some people have given to the yellow coating covering your car, your deck, and everything else outside when plants release their annual load of spring pollen. Even the sky becomes an unusual shade of chartreuse. It's everywhere, and there's nothing you can do to avoid it. You try to stay indoors, but sometimes even that doesn't work. After all, pollen grains are microscopically minute.
(Colorized scanning electron microscope image of pollen grains from a variety of common plants;
It goes something like this: allergies and asthma throughout North America worsened because landscapers and city planners thought male trees were easier to maintain. City planners, who are mostly male, decided female trees are too messy. They planted an overwhelming number of male trees that release pollen, but not enough female trees to capture it. Therefore, we have more pollen floating around in the air than ever before, leading to the increase in allergies.
That TikTok post has nearly 800,000 likes and was shared 34,000 times. What people failed to mention is the real reason female trees are considered messy. It's because they produce fruit.
A prominent horticulturist and allergy researcher first coined the biological sexism phrase in an article for Scientific American. The article references the 1949 USDA Yearbook of Agriculture that says, “When used for street plantings, only male trees should be selected, to avoid the nuisance from the cottony seed".
However, the USDA reference applies to cottonwood trees only. These trees are dioecious, which means it takes two to tango. The male and female parts are found on different trees. The reference goes on to say female cottonwoods are dangerous for street planting because they clog drain pipes and can block sewer systems. Interpreting the yearbook passage to imply that the USDA recommends the use of only male trees for all urban planning is intentionally misleading.
Female trees do not produce pollen, but they do trap and remove large amounts of it from the air, producing seed. Female trees and female shrubs actively fight allergies. The more female plants in a landscape, the less pollen floating in the air.
According to the Asthma and Allergy Foundation of America, allergies are the sixth-leading cause of chronic illness in the United States. Inflammation caused by allergic reactions to outdoor plant triggers affects 5.2 million children and about 19.2 million adults. Other research suggests that a high tree pollen count in a city directly correlates to asthma-related emergency room visits.
In nature, a balance exists between male and female plants. But in many cities and municipalities, that balance is missing. Male trees are the majority. The remedy for deadly allergies is to plant more female trees within a given area in order to achieve gender balance.
Using a system called the Ogren Plant Allergy Scale (OPALS™), people can select plants ranked on a scale of 1-10 when they need or want to plant an allergy-compatible space. The USDA has implemented OPALS, and the 2015 book, The Allergy-Fighting Garden, explains how to use it.
The debate continues
Penn State University professor William Elmendorf, a specialist in community and urban forestry, confirms that Ogren’s recommendations are correct. Dioecious varieties have distinct male and female specimens. However, he goes on to say that instead of human sex pronouns, terms like podless or fruitless have historically been used to distinguish dioecious trees, such as gingko, locust, and Kentucky coffee tree, that are specifically propagated to produce little or no fruit. He stresses placing the emphasis on species diversity and not on male-female botanical traits.
However, others claim it is excellent environmental stewardship to plant a predominance of male dioecious trees in urban settings. Seeds of fruiting trees like ginkgo are toxic and can poison waterways when washed down storm drains into a water source, which is often a stream or river. The fruit of some female trees can make city sidewalks sticky, slippery, and dangerous for pedestrians.
Public health is also a factor. The seeds of female ginkgo trees cause symptoms similar to food poisoning. Urban planners may choose not to plant specific trees in order to protect the public.
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