The most widely planted shade tree in school yards across America is the "fruitless" mulberry tree, a male clone of white mulberry. They grow big and fast and are easy to grow. These trees produce no messy mulberries, but they are among the most allergenic of any city trees, and each one sheds hundreds of millions of grains of pollen each year. Each individual pollen grain from the male mulberry trees is microscopic in size, easily inhaled deeply into the lungs, hence perfectly capable of triggering asthma attacks.
According to the American Academy of Allergy, Asthma and Immunology, more than 34 million Americans now have asthma, and the numbers have almost doubled since the late 1970's. Asthma rates for young children have increased by more than 150% since the mid-1980's. At least 70% of people with asthma also suffer from pollen allergies.
Some 13 million school days are missed each year because of asthma, and more than 3,000 people die from it each year in the US, many of them children. It was formally estimated back in 1999 that some 39% of Americans had developed allergies, and those numbers are still increasing. The costs directly related to allergies and asthma from missed work, missed school, doctors' visits, medicine, and ER visits amounts to many billions of dollars each year.
Second in popularity among shade trees planted in school yards is the London Plane tree, or its close cousin, the Sycamore. Not as allergenic as the male mulberry trees, these London Planes and Sycamores nonetheless do shed considerable allergenic pollen each spring, and much of the year their fuzzy leaves also shed multitudes of microscopic, sharply pointed plant hairs that make school children and their teachers itch, scratch and cough.
In the Midwest and in the East a third tree has become extremely popular as a shade tree for city schools, the Norway Maple. In all of horticulture there probably is no single tree that has as many different cultivars (cultivated varieties) of it in the nursery trade as the Norway Maple. A big, fast-growing, dense shade forming tree, the Norway Maple is a big pollen producer, and its pollen is especially allergenic. In recent years across much of its range, Norway Maple trees are now commonly afflicted each year with leaf blight. The blight makes the leaves look spotted and ugly, but far worse, spores from the blight, a fungal disease, these spores, much like the closely related spores of mold, they can trigger episodes of both allergy and asthma.
The most commonly planted shrubs in and around school yards are junipers in the West, and yews in the East. In both cases male clones are almost always used, and each of these clonal selections produce considerable pollen, pollen that is both very allergenic, and in the case of the yew, also toxic.
What is most evident in the planting of so many school yards though, is that when the existing trees were originally selected, no one gave much thought to how they would eventually affect the health of the children playing in those same school yards. Is it any wonder that across America and Canada, asthma is now the number one chronic disease affecting school children?
So, what is to be done about this unhealthy situation? Obviously the current situation is not sustainable; something needs to change, sooner, rather than later, if we are truly concerned about the health of our school children.
Three years ago the author was contacted by a doctor in Christchurch, New Zealand, who was very concerned about the allergy-causing trees planted at the public elementary school his daughter attended. The doctor's daughter, then age 9, suffered from both pollen allergies and allergic-asthma. Just prior to this a great deal of press had been devoted to the many thousands of non-native silver birch trees that lined streets of Christchurch, and to the terrible pollen-allergies these same trees caused so many people each spring.
The school in question had a large row of silver birch trees that ran directly through the elementary playground.
The doctor requested that the school district remove the birch trees and replace them with low-pollen trees. His request was denied, so the doctor took the school district to court. In the process I was asked to submit expert testimony, which I did.
My advice was this: Silver birch trees are beautiful trees, and in some places are perfectly suitable, but they don't belong in school yards. Trees are important, certainly, no sane person would deny that, but our children are more important. My advice was that the trees should be removed, and that they should be replaced immediately with pollen-free trees, using as large-sized new trees as was feasible.
The end result was this: the court found in the doctor's favor, the silver birch trees were removed, and they were replaced with good-sized Red Maple trees, using the cultivar "Autumn Glory", which is a female, pollen-free variety. "Autumn Glory", which is valued for its marvelous display of fall color, was already known to thrive in Christchurch. Today, just a few years later, these new allergy-free trees are already getting big and are providing needed shade at the school. And best of all, the children are no longer exposed each spring to a bombardment of allergenic birch pollen right there in their school yard.
It shouldn't take a lawsuit to get school districts to plant allergy-free trees, but sometimes that is about the only thing that will make them take notice.
A dozen years ago in Albuquerque, New Mexico, an elementary school boy was playing at the city zoo and fell into a planting of male juniper bushes. Male junipers produce abundant pollen, often several times a year, and their pollen is quite potent. The boy went into anaphylactic shock and soon died. Someone who understood about plant sex and the effect it can have on human health said this to the boy's parents, "The city's landscape killed your son."
The parents sued the city and the case was settled out of court for an undisclosed sum of money, but as part of the settlement, the city agreed to put a ban on the sale or planting of any more male cloned trees and shrubs. Albuquerque hence joined the ranks of cities with pollen-control ordinances. However, the same sort of allergenic trees and shrubs that planting would net you a $500 fine in Albuquerque, these same allergenic plants are still being planted every day by well-meaning, but misinformed adults, in school yards all across the US and Canada.
Last year I was asked to write an Op-ed piece on city trees and allergies for the New York Times (see: http://www.nytimes.com/2010/04/06/opinion/06ogren.html ) The article provoked a good deal of heated discussion, but the city commissioner in charge of tree planting dug in his heels and declared that, "Trees are good." He made no promise to even try to plant fewer high allergy trees, and more allergy-free trees. It is unfortunate, but change doesn't seem to come unless people take charge, and demand changes.
When it comes time to plant trees, for every high allergy tree there is also a perfectly fine low-pollen, or even a pollen-free tree that could be selected. Certain trees and shrubs are locked into permanent juvenility and never bloom; they're allergy-free. Other trees and shrubs are separate-sexed, and with these species the female plants never produce any pollen at all. Certain hybrid trees and shrubs never produce any pollen. There are many possible low-allergy choices to select from. For over a decade now OPALS™ has been in existence, an easy to use, 1 to 10 allergy ranking system of thousands of commonly used landscape plants, where 1 is least allergenic, and 10 is the worst.
There is a phrase I first coined, now used in scientific journals devoted to pollen allergies, called "proximity pollinosis." Simply, what it means is this: the closer you are to an allergenic pollen producing tree or shrub, the greater will be your exposure, and your chances of having related health problems. It makes no sense at all to plant highly allergenic trees or shrubs in school yards.
I would appeal to all parents of school children: do not wait until your own school district decides to start using allergy-free landscaping practices & demand that they start doing so right now.
The Allergy Free School Yard© is the initiative of Peter Prakke, of Ancaster, Ontario, Canada. He began working on this when he realized the contradiction inherent in the statistic that more and more people are suffering from allergies and asthma, while we're trying to promote a healthier outdoor life. He decided it was time to do something to make it less of a challenge for everyone to enjoy the outdoors, especially children.
The author, Thomas Leo Ogren, has published six books and hundreds of articles on plants and human health. In 1999 he landscaped the American Lung Association headquarters with an allergy-free landscape. For over a decade the USDA has used OPALS™ in their research projects on urban allergies. Tom has been interviewed several times on NPR, on the CBC and on the BBC, and his work has often appeared in scholarly scientific journals and popular publications such as The London Times, Der Spiegel, and The New Scientist.
Co-contributor to this article, retired life long nurseryman, horticulturist, lecturer, and award-winning public educator, Peter Prakke, has recently been instrumental in getting school districts in Hamilton, Ontario, Canada to start planting only allergy-free trees and shrubs in their school yards. Peter first started the Allergy-Free School Yard© initiative and he can be reached at: http://www.healthyschoolyards.org