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Ragweed found to spread easier along roads with high traffic

Friday, April 16th 2021, 1:48 pm - The findings could help city planners devise ways to stop the spread of ragweed.

Ragweed is common in southern Canada, and seasonal allergy sufferers can usually tell when it's in bloom.

During ragweed season, one plant can release a billion grains into the air, causing symptoms like stuffy noses, sneezing, and itchy eyes. And in asthma sufferers, it can tricker attacks.

Though native to Canada, ragweed is invasive in parts of Europe. And now, a new study from Andreas Lemke, Sascha Buchholz, Ingo Kowarik, and Moritz von der Lippe of the Technical University of Berlin and Uwe Starfinger of the Julius Kühn Institute have found human activity might help the plant proliferate.

The paper mapped 300 km of roadsides in the German state of Brandenburg, a ragweed hotspot, and found ragweed grows exceptionally well along roadsides that experience heavy traffic.

That explains a lot, researchers say. Ragweed has a natural dispersal rate limited to around 1 metre -- but it's expanding across Europe rapidly, suggesting other factors are helping it along.

Common ragweed

Common ragweed is an annual plant whose allergenic pollen affects human health. It's an invasive species particularly well-adapted to living at roadsides. New research, published in in the open-access, peer-reviewed journal NeoBiota, found high population growth along high-traffic roads even in shaded and less disturbed road sections, suggesting that seed dispersal by vehicles and by road maintenance can compensate, at least partly, for less favorable habitat conditions. {Caption courtesy} | photo courtesy: Uwe Starfinger CC-BY 4.0

The scientists looked at roadways over five years, recording plant densities and noting habitat diversity.

"Surprisingly, high-traffic road cells displayed a consistently high population growth rate even in shaded and less disturbed road sections - meaning that shading alone would not be enough to control ragweed invasions in these sections," the authors say.

"Population growth proceeded even on roadsides with less suitable habitat conditions - but only along high-traffic roads, and declined with reduced traffic intensity. This indicates that seed dispersal by vehicles and by road maintenance can compensate, at least partly, for less favorable habitat conditions."

This could help city planners devise a plan to stop the spread of ragweed, including an increased mowing routine and planting dense, native vegetation that can outcompete ragweed.

The findings have been published in the journal NeoBiota.

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