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Yes! In my travels as an officer of ISA, I frequently hear about and witness examples of arboreal sex discrimination. Many official city tree lists clearly specify preferred trees as male or female.

However, when purchasing trees or shrubs, home owners do not ask the nursery or garden center for a male or female variety. They may ask for pollen- or allergy-free trees or plants—or even for litter-free trees and plants. Trees can be pollen-free if they are a dioecious species and are female. One can avoid the litter of fruits, pods, seeds, and other reproductive debris by installing male dioecious plants—or female plants where there are no males for pollination. Proximity seems to be the key to this strategy because some pollen simply travels farther. And, despite our best efforts to avoid pollen and debris, most tree species are actually monoecious, having both male and female parts on the same tree. Inbreeding by monoecious plants and trees would seem to be a fertile area for research. I have heard Alex Shigo state on many occasions that “We don’t know enough about trees!” Obviously, we don’t! But, let’s not rush to judgment and totally blame male trees for allergies, asthma, and other respiratory system problems.

In an article in USA Weekend magazine (September 9, 2001), Todd Mitchell, a medical doctor, stated that if you are predisposed to having allergies (in other words, if you are diagnosed with atopic allergic hypersensitivity), you may want to move to a drier, more moderate climate where pollen counts are lower. Further, if you are a parent, Dr. Mitchell recommended that you not confine your kids to a spotless home to protect them from allergens. Scientists say that childhood exposure to dirt could train “T” cells, the infantry soldiers of the immune system, to bulk up against air and dirt allergens that will be inhaled later in life.

According to the Allergy, Asthma and Immunology Division of the Scripps Clinic in La Jolla, California, about 50 million Americans in 1999 had allergies to a variety of substances such as pollen. Other top allergens include peanuts, latex rubber, mold, stinging insects, shellfish, dairy products, and pet dander. The point being made here is that there are other causes of allergies beyond plant pollen.

Linda Ford, one of the nation’s leading allergy experts, says that she is well aware of the sexual politics of pollen. Dr. Ford served as chair of the American Academy of Allergy, Asthma and Immunology. Dr. Ford agrees that male plants are connected to allergies because they produce pollen. She also states that it does not make any difference because pollen blows around and displaces, so the sex of a particular plant is not the only factor. For example, global warming has changed pollen. Temperature changes caused by the greenhouse effect and increasing levels of smog (filled with carbon dioxide) in the inner cities have created more robust plants. The hot, smog-heavy plants are believed to produce more pollen. Dr. Ford also states that the reason allergies and asthma are increasing is multifaceted. We also have the problem of carpeting in homes and animals (pets) that once lived outside now living indoors.

Here’s some more food for thought about allergies. This information comes from The Skeptical Environmentalist by Bjorn Lomborg, associate professor of statistics in the Department of Political Science, Aarhus, Denmark:

• The British Medical Journal concluded that, despite the massive number of scientific studies, “the evidence for increased prevalence of asthma and wheezing is weak because the measures used are susceptible to systematic error.”
• It is also important to find out what causes asthma. It is to a large extent genetic because our genes partly determine whether we have a sensitive or “thick-skinned” immune defense system.
• It is estimated that around 380,000 asthma cases in the United States are caused by parental smoking.
• We also know that since the energy crisis began, we have dramatically increased the insulation of our homes to cut heating bills. Today, the indoor air in our homes is replaced, on average, ten times less frequently than it was 30 years ago. This lack of air replacement has led to a marked increase in atmospheric humidity and in the concentration of dust mites and other allergens.
• More and more researchers are beginning to agree that developing asthma is probably caused by a whole series of changes in our lifestyle.

Considering the variables in the causes of allergies, there does not seem to be much value in promoting an exclusively female tree and shrub population (or, for that matter, an all-male population). Without pollen from male trees, female vegetation could not produce colorful and healthy fruits, which are valuable assets for ornamental trees and shrubs. Fruiting ornamentals also attract wild birds, serving as viewing pleasure for home owners and bird watchers. Beneficial insects that rely on male pollen for survival would also suffer.

So, what is the answer to this dilemma of arboreal sex discrimination? We use the term “ecological system” to describe the organization and interaction of communities of living things, including humans, with the chemical and physical factors in their environment. Ecosystems are complex, dynamic, and ever changing. In natural ecosystems, there is a gender balance, with about equal percentages of each sex that interact to produce. Among other factors, species diversity also contributes to the stability of the system.

The same reasoning should apply to the urban ecosystem, except that change occurs as the result of human influence. Human activities result in direct and indirect impacts—both beneficial and adverse. To enhance benefits, public health, well-being, and, yes—economic vitality—we must have balance in the urban ecosystem. Meaningful, progressive, public education programs seem to be the logical answer.

Obviously, there is much more to the issue of pollen allergies and arboreal sex discrimination. Space simply does not allow for a comprehensive article, and additional research is necessary.