When city arborists began planting predominantly male trees along streets fifty years ago, they were more concerned with keeping fruit and litter from clogging the gutters than aggravating allergies. However, recent theories suggest that pollen released from these male trees may be the cause of increased asthma and allergies in urban areas.

?EUR??,,??Because ?EUR??,,??litter-free?EUR??,,?? landscapes are now highly desired, trees, shrubs, and ground covers that do not make a ?EUR??,,??mess?EUR??,,?? are preferred,?EUR??,,?? wrote Landscaper, teacher and writer Thomas Orgen of San Luis Obispo, Calif. on the Society of American Foresters website. ?EUR??,,??These seedless, fruitless, or cottonless plants are typically asexually propagated male clones. Virtually all of the dioecous [species with male and female flowers on separate plants] are primarily wind-pollinated, and with almost all of these, the male trees produce copious amounts of allergenic, airborne pollen.?EUR??,,??

Orgen admits that the problem may be worse in some areas than others, and some cities, boast trees that are more androgynous, therefore, less aggravating to allergies. However, tree variations that are believed to cause allergies include cottonwood, willow, elm, aspen,maple,poplar, and oak, which was just named America?EUR??,,??s National Tree by the National Arbor Day Foundation.

That most of the trees in many urban areas are male creates a powerful pollinating system when coupled with the tendency to plant monocultures along streets.

?EUR??,,??Urban landscapes often lack biodiversity, which leads to allergies and other problems,?EUR??,,?? said Orgen. Typically, entire streets will be lined with exactly the same kind of tree, resulting eventually in ?EUR??,,??pollen corridors?EUR??,,?? there and resulting in allergies.?EUR??,,??

Although other professionals agree that urban forestry often includes trees cultivated for form, color, flowers, low or high fruit production, pest resistance, and so-on, David Nowak of the USDA Forest Service Northeast Research Station claims that there is no evidence to reject nor support Orgen?EUR??,,??s claim.

?EUR??,,??From a field sampling, we are starting to get an understanding of species composition and distribution throughout urban areas,?EUR??,,?? explained Nowak. ?EUR??,,??We are using these data in conjunction with Mr. Orgen?EUR??,,??s tree species pollen index values to estimate overall urban forest pollen index values for various cities.?EUR??,,??

However, Orgen sees the pollen problem to lead to a decrease in residents?EUR??,,?? appreciation of trees.

?EUR??,,??The credibility of the nation?EUR??,,??s urban foresters is involved here, too.,?EUR??,,?? he states. ?EUR??,,??Will they step up to the plate and try to deal proactively with this perfectly real and serious problem, or will they just continue to ignore it??EUR??,,??