2018-06-28 / Nature

Airborne Seeds Invade in Untold Numbers

By Charles Avenengo

While sitting on a bench at Aquidneck Park earlier this week, attempting to enjoy what little warmth available, I noticed the air was alive with movement. Because the day was sunny and windy, a number of objects were in flight. In addition to the birds, the sky was filled with what I first thought were insects. Upon closer inspection, the objects turned out to be windborne dispersal seeds scattered from the park’s various trees.

Like Bob Dylan’s 1962 pop hit “Blowin’ in the Wind,” the breezes were steering the seeds in all directions. On this day, the projectiles were emanating from the Littleleaf Linden trees that line the Spring Street side of the park in front of the Newport Public Library. I was witnessing an airborne dispersal that literally is the fabric that creates forests.

“There certainly is a spring bloom,” said Newport Tree Warden Scott Wheeler, referencing the airborne flotilla. “The amount of ash, oak and elm seeds are staggering. This is essential for tree regeneration.”

Wheeler said that over Aquidneck Island’s five centuries of human activity, while the woodlands have been denuded for various reasons, the forests have always returned in various stages of succession.

“If you look at Ocean Drive from the sea, you see a contiguous forest,” said Wheeler. “Only a tiny percentage of it was planted by man. This natural regeneration is how Aquidneck Island became reforested.”

The regeneration process of airborne seeds can be placed into different categories, including gliders, helicopters and flutterers, parachuters, cottony seeds and tumbleweeds.

The gliders and helicopter seeds are similar, with lateral wings that resemble those of an airplane. When released from the tree’s fruit they sail through the air like a true glider or rotate to earth like a helicopter.

The seed of one species of climbing gourd in Asia, the Alsomitra macrocarpa, is five inches in length. It drifts through the air in wide circles and reportedly was the inspiration for the design of early aircraft and gliders.

The seeds that drop from maple trees are everybody’s favorite. Many people have tossed the so-called whirlybirds into the air and watched them spin back down to earth. Perhaps Igor Sikorsky, the grandfather of the late Sergei Sikorsky of Newport, and a pioneer of early helicopter flight, studied this phenomenon to create the prototype rotorcrafts.

The free fall of parachute seeds is more associated with plants like dandelions and sunflowers. Seen through a magnifying glass, the puff balls look like umbrellas and the slightest hint of a breeze can send the “floaties” as far as the wind allows.

Another type of windborne scattering is the cottony seeds. Currently, a number of trees and plants employ this technique for dispersal. Most notably are the cottonwood trees that release their characteristic seeds and fill the air with fluff that looks like tiny white clouds. In places where there is a large volume of cottonwood trees, it can look like there is snow on the ground. The number of cottony seeds can be staggering. A single spike of a common cattail can release a million cottony seeds, and each could pass through the eye of a needle. Researchers have estimated that a single acre of a cattail marsh can produce one trillion seeds.

Finally, there is the tumbleweed. While not exactly airborne, tumbleweeds are certainly windborne. As they are pushed along, they also scatter thousands of seeds in their wake. Surprisingly, these iconic symbols of the American West are naturalized in North America. They were introduced into the United States in the late 1800s from southeast Russia.

Sitting on the park bench and reflecting about the airborne onslaught, I began to consider writing about the spectacle. But given the many pollen sufferers, I worried. Later, when I began to investigate the topic, I learned that pollen is microscopic. In botanical terms, the unicellular pollen is the expedient for plants to fertilize. Seeds are the end product. Since I wouldn’t be praising pollen, but rather airborne seeds, I felt I was safe.

On this day, as the seeds were dropping onto Aquidneck Park by the hundreds, I calculated that this seemingly endless army of seeds was raining upon Newport by the thousands. Translated further afield, well, the numbers are incalculable.

“My old professor used to say, if you abandon a shopping mall, 50 years later, it will be a forest,” Wheeler said.

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