Post by guest blogger Tom Ogren, who has a MS Degree in Agriculture/Horticulture and is an expert on the connections between landscape plants and allergies/asthma, having studied the topic for more than 25 years. He loves birding, fishing, camping, traveling, and collecting data on pollen-free plants. Tom is the author of “Allergy-Free Gardening: The Revolutionary Guide to Healthy Landscaping.”
A Lack of Balance
A few months ago, I was in Sacramento for a conference, and was fortunate to have some time to spend on one of my favorite activities: surveying a city’s trees.
From willows, poplars, and aspens to yews, pistaches, and so many more, the city has so much variety. It’s no surprise that Sacramento is known as the “City of Trees.” Even in late fall when many leaves have already fallen, the city’s trees color the sidewalks and skyline, drowning out the concrete grayness that plagues so many urban areas. And they provide so many other benefits, too, from livening up the Old Sacramento Historic District to shading homes in scorching Sacramento summers.
But, as a pollen-allergy researcher, I couldn’t help but view this treescape from another angle: Just how were all those trees affecting the air Sacramentans breathe and their health?
You see, among certain species of plants, the female plants make fruit, seeds, pods, or berries while the male plants make no seed or fruit at all, but instead make a very large amount of pollen—and it’s often quite allergenic. These species are known as separate-sexed or dioecious.
In my years of research, I have found that in cities across the globe with these separate-sexed species, there are usually a disproportionately large number of male trees and shrubs. Why? Because people want “litter-free” trees—free of fruit, seeds, or berries.
But, are these male trees really so tidy? Not exactly—in fact, each one sheds a large amount of pollen. Because male trees do not trap or remove any pollen like females do, that pollen count has grown larger each year in urban areas—and so has the number of people suffering from allergies and allergic asthma.
Restoring the Tree-quilibrium
So, is there a solution? Can we urban dwellers enjoy the many benefits of trees without increasingly severe allergenic side effects?
Absolutely! The answer, you might say, lies in the balance.
First, as cities, businesses, and homeowners, we can stop planting any more clonal male trees in urban areas, and start planting large numbers of female trees of the same species. Worried about fruit or seeds? Don’t be! Without male trees, females won’t produce them.
Once we restore the balance that nature intended—a tree-quilibrium, if you will—we’ll likely see our urban allergy and asthma rates decline. If male trees continue to vastly outnumber females, however, we can expect more and more pollen to remain in our air, untrapped by females, continuing to exacerbate our allergies.
Second, we should embrace the simple, easy-to-use plant allergy scale, called OPALS™, that’s been in use for over a decade now. The scale ranks all landscape plants from 1-10, from least allergenic to most. More cities and groups should join the ranks of the American Lung Association, asthma coalitions, the USDA Urban Foresters, and others who are already using it as a road map to a greener and allergy-friendlier future.
Lastly, while we’re at it, why not also start using more fruit trees as landscape trees? Low on the OPALS™ scale, they’re some of the smartest, friendliest investments we can make in our cities’ land—and air.
By pursuing some of these easy-to-implement suggestions, we can together ensure that our cities are not only greener, but that their air is cleaner. Doing so is a wise investment in any city’s health and wealth.