On Saturday the Times published two letters that responded to its recent op-ed piece by Thomas Lee Ogren on trees, pollen, and allergies.
One reader, Christine Lehrer, wrote:
Honeybees collect pollen from the very trees that are causing all the sneezing and runny noses. By taking a spoonful of honey daily, approaching and during allergy season, you inoculate yourself against the offending pollen and greatly reduce your allergic reaction.
Another, Joan Edwards, wrote:
Plants with showy colorful flowers like magnolia, black cherry, redbud and flowering dogwood … make pollen that is designed to affix to their pollinators. Their pollen is sticky, produced in small quantities, and large so it is less likely to be blown in the wind, where it can be inhaled by an unsuspecting passer-by.
Both of these cannot be true. My money is with the Edwards: Bee-pollinated trees don’t bother to release the kind of pollen that makes you sneeze, and wind-pollinated plants don’t bother to attract bees. (There may be belt-and-suspenders plants out there that can be pollinated by wind but would like also to be pollinated by bees, but this non-botanist isn’t aware of them. Readers?)
So by planting only insect-pollinated trees and the female cultivars of wind-pollinated trees, we can reduce pollen counts. Good information, as far as it goes, but neither Ogren nor Edwards successfully addresses the other qualities that urban trees require. Ogren writes:
In New York City, street trees are selected only for their hardiness in winter; their resistance to disease, insects and drought; their ability to withstand smog; and their size, shape and color.
Even when selecting ”only” for those criteria, the trees that pass muster make up a pretty short list. Adding a new criterion will only make the list shorter. And in fact, very few of the trees that Ogren and Edwards recommend would perform well as street trees.
It turns out New York’s criteria make sense. Size, for example, matters. A big tree does more to keep a city cool and clean than a small one does. It casts more shade, transpires more water, absorbs more noise, and (if its leaves are fuzzy) traps more particulates. Plus, a sidewalk tree’s lowest branches have to be higher than a tall pedestrian’s head, so the tree has to be large enough that it can be limbed up without looking like a broken umbrella.
Trouble is, most big trees are wind-pollinated. (Evolutionary biologists, pitch in here: Is it because more insects fly at dogwood-height than at oak-height, or are there some other phenomena at work? What is it that the tall insect-pollinated trees — tulip poplar, cucumber magnolia, caltalpa, horse chestnut — have in common?) Whatever the benefits of planting only the kinds of trees that don’t release a lot of pollen, our urban forests would be poorer for it, and our cities would be hotter, to the detriment of trees and people alike.
Instead of banning wind-pollinated trees altogether, what about mapping prevailing spring winds and vulnerable populations (schools, hospitals?), and designating zones in each city where only female and bee-pollinated trees would be planted? If we can put some allergists and public health specialists in the same room as some planners and urban foresters, we might get somewhere on this.
In the meantime, stir a little local honey in your tea. Probably won’t help. Can’t hurt.
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Deborah Howe
Toby Wolf
