In the US and Canada there is a massive problem in cities caused by an excess of male trees and no females
TL;DR: City authorities find it resource-intensive to clean up fruit and seeds from femaie trees, and so have for many years only planted male trees, whose pollen blows away. This increases the amount of pollen in city air enormously, exacerbating asthma and other breathing-related conditions.
I wonder whether London has the same policy.
https://twitter.com/Flaminhaystack/status/1257648064954761216
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