|
How Bad Is Allergy Now?
In 1959 the official rate of allergy in the U.S. was between 2 to 5% of the public. By 1999 the official rate of allergy had
increased to an incredible 38% of Americans. Asthma, which was once considered rare, is now the number one chronic childhood disease in the
US.
Where are Allergies and Asthma the Worst?
The most common allergen of all is pollen and since there are so many more plants growing in the country than in the city, it would make sense
then that there is more allergy and asthma in the countryside. Right? No, wrong! Allergies and asthma are far worse in the city than they are in
the country.
Several things contribute to this:
1.Pavement makes a poor pollen trap. Pollen in the city often lands on pavement where wind can cause it to become airborne again. In naturally
vegetated areas where there is much more vegetation, pollen often lands on and becomes stuck in grasses, shrubs and vines or in trees.
2.Cities have more air pollution, which weakens the immune system and lung function.
3.Stress, which is generally higher in cities, can contribute to both asthma and allergy development.
4.Increased carbon dioxide levels within cities causes pollen-forming plants to produce more pollen with each bloom cycle, and also often causes
urban plants to bloom more often.
5.Pollen loads are actually far greater in cities because there is a sexual imbalance within the plant community. In the city there is a
preponderance of male trees and shrubs, while in the rural areas there is almost always a complete balance of plant sexuality. The excess of male
plants in the city results in an excess of pollen.
6.The very lack of female plant materials in the urban environment also is a prime factor in the epidemic of allergy and asthma. Female flowers
carry an electrical negative (-) charge (the trees are grounded with their roots) and airborne pollen holds a positive (+) charge. The tree and
the pollen are mutually attractive; thus a female plant becomes a very effective pollen trap for pollen of its own species. But with almost no
female trees and shrubs in modern landscapes, most of the pollen remains airborne.
How to Improve Health and Air Quality through Tree Selection
Landscaping to reduce allergies, especially pollen allergies, is an idea that is coming into its own. In the past few years several books have
been written on the subject and interest is growing rapidly.
With the addition of OPALS™, (Ogren Plant-Allergy Scale) arborists now have a means to design allergy-free plantings. This scale ranks all
landscape plant materials on a simple 1 to 10 allergy basis. Trees that produce zero pollen, e.g., female cultivars, usually rank the best –
number one. Trees that have abundant, highly allergenic pollen, especially those with very long bloom periods, are usually ranked the worst – in
the 9-10 range. There are many trees and shrubs, however, that fall somewhere in between. Using a list of over 100 factors, OPALS™ numerically
ranks each species and then further ranks the individual cultivars. There are often dramatic allergy differences even between two species in the
same genus.
|