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CO2, Tidy Sidewalks, and Pollen-Filled Air

by: Tom Ogren

CO2, Tidy Sidewalks, and Pollen-Filled Air

The increasing level of CO2 (carbon dioxide) in our air is already contributing to soaring allergy rates, and we can expect it to get much worse. Some claim this extra CO2 is good—that it will result in increased plant growth and in increases in global food supplies. While there is some merit to this theory, the additional CO2 is certain to trigger some incredible pollen allergies.
Greenhouse owners have long understood that plants consume CO2 and release oxygen. When plants in a packed greenhouse use up most of the available CO2 their growth stops. Old-time growers used to place flats of fresh manure underneath their greenhouse benches. As the manure decomposed it released CO2 into the greenhouse air and the plants grew faster.
Modern greenhouse ranges, equipped with automatic gas regulators, monitor the amount of CO2 in the air and release more as needed. In these greenhouses plants don’t just grow bigger—they mature earlier and produce more flowers.

Since the 1950’s allergies have increased from 2 to 5 percent of the population, to 40+ percent now. Each year deaths from asthma continue to rise. “Litter-free” landscapes, loaded with wind-pollinated trees and shrubs, now dominate vast urban areas and produce unnaturally large amounts of allergenic pollen. Because the “messy” urban female trees are now so rarely used, less of this urban pollen is trapped, removed from the air and turned into seed. (Female trees produce no pollen, but they do trap pollen, turning it into seeds, pods, and fruit, i.e. litter.)
Even under normal carbon dioxide levels male street trees always produce abundant pollen. With increased levels of CO2, they produce considerably more. These clones can not produce pollen until they reach sexual maturity, but with the current increases in CO2 levels they will mature prematurely.
Increases in carbon dioxide promote plant growth but only if there is enough available extra water and nitrogen in the soil to support this additional growth. When supplies of water and nutrients are inadequate to support additional CO2-induced growth, alarming physiological stresses occur.
A stressed lemon tree, for example, will often produce a huge crop of tiny, very seedy lemons. This is simply the lemon tree’s way of preparing for its imminent demise and its own legacy of seedlings.
In university experiments pine trees and weeds grown with elevated levels of CO2 bloom prematurely and produce three times the normal amounts of pollen.
Pollen-bearing landscape shrubs, such as male junipers, which normally bloom only in the spring, are now often blooming twice a year. This is increasingly happening also with urban birch and alder trees.
Continued use of high allergy landscapes combined with ever increasing levels of CO2 may well be the recipe for allergies of true epidemic proportions. We must pay closer attention to how we landscape our cities and get serious about alternative clean energy sources, or rampant allergies will surely result. This could be a gold mine for the producers of Allegra and Claritin, but it would be a wheezy, sneezy nightmare for the rest of us.

Thomas Leo Ogren is the author of Allergy-Free Gardening

Thomas Leo Ogren is the author of Allergy-Free Gardening, and, Safe Sex in The Garden, both from Ten Speed Press. Tom has an MS degree in Agriculture/Horticulture, with an emphasis on plant flowering systems and allergy. He is a former horticulture teacher, landscaper, nursery owner, and in Minnesota was the host of the popular call-in Public Radio show, “Tom Ogren’s Wild World of Plants.” He can be contacted through his website at

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(Added: Sun Sep 25 2005 Hits: 1054 Downloads: 0 Rating: 0.00 Votes: 0)   Rate It   Review It


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