This is the first part of a series discussing the factors involved in designing for low allergy landscapes
“Our modern landscapes actually are killing us,”
says Thomas Leo Ogren, author of “Allergy Free Gardening. The Revolutionary Guide to Healthy Landscaping.”
Ogren has a master’s degree in agricultural science, is a former landscape gardening instructor, nursery owner and gardening radio host. In his book, “Safe Sex in the Garden (and other propositions for an allergy-free world)” he describes what he believes are some of the causes for the rise in allergies in the United States. Ogren relates how, over the past 30 years, the number of people suffering from allergies in the United States has risen from 2-5% to 30-40% of the population with the most widespread increase in diseases from allergies from plants. It turns out that there are a number of factors that have led to this increase in allergies, and for Ogren, the most serious is the human allergic reaction to the massive increase in pollen production. So why is there such a huge increase in pollen production? Countries from all over the world monitor airborne pollen and allergy symptoms and have determined that some the major factors in the dramatic rise in pollen productions are:
- Lack of Urban Planning
- Poor Choices in Plant Selection
- Botanical Sexism
- Global warming
Lack of Urban Planning
As cities and urban landscapes have grown, urban landscapers, developers and landscape architects have planted trees as a way to beautify the landscape and to help remove carbon dioxide and pollutants from the air. Research has shown that lower levels of domestic violence are recorded amongst residents living in areas with trees and that going outside in nature, leads to lower blood pressure and stress reduction. Cities and towns have invested heavily in the ‘greening ‘process as the solution to problems with pollution and air quality. Paradoxically, this has led to many of the health problems that now plague our communities. So how did this happen? How could investing in planting trees in our cities undermine the quality of our lives?
Poor Plant Selection
Problems arise when only a few species of trees and shrubs are selected and planted in the urban landscape: species diversity is positively correlated with higher quality of life. Too many of the same species in city spaces has a detrimental effect on the population. Some of the trees selected for urban cities produce enormous amounts of pollen with demonstrated allergic properties; some release volatile organic compounds (VOC) which combined with carbon dioxide and warmer weather, create smog. In some newly urbanized areas, many of the native trees and plants have been have been displaced by exotic and invasive species which have given rise to new sources of pollen allergies for local residents. Additionally, there is an increase in the use of male trees which are selected from asexually propagated clones that are pollen intensive.
Ogren (2000) writes that the increasing incident of pollen allergies in the urban environment is directly linked to botanical sexism.
“For reasons of convenience, more and more shrubs, trees and other plants are selected for their ‘litter-free characteristics’ that is-they are male types and generate no seeds or fruits”
When male trees are massed together with no females, the male trees produce even more pollen in an effort to reach and propagate a female tree. The rationale for seeking out “seedless” varieties is that seeds, berries and fruit are messy, may have an undesirable odor (such as the fruits of the female Gingko tree) attract insects, and cause slippery surfaces. Keep in mind that the male Gingko tree, on reaching maturity at approximately 10 years old, releases large amounts of pollen with a demonstrated allergenic capacity.
Global warming, with increased carbon dioxide and an earlier, warmer spring has led to earlier and longer pollen production from the males. Dr. Clifford Bassett, founder and medical director at Allergy and Asthma Care of New York predicted a “very robust pollen explosion” for the spring of 2015 -and he was right. “There are a couple of factors,” Dr. Bassett told weather.com. “One is the rising long term increase in carbon dioxide and its effect on increasing pollen production.” Another is what he calls the battle of the sexes: pollen producing male trees are dominating greenspaces in many cities.
Next Post : The rise of allergies in the residential landscapes and recommended plants for a low-pollen, low- allergy landscape