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tl;dr Male trees were planted disproportionate to female trees in urban settings because they didn't shed messy seeds. The preponderance of male trees increase

tl;dr Male trees were planted disproportionate to female trees in urban settings because they didn't shed messy seeds. The preponderance of male trees increases the amount of pollen exposure. Author asserts this leads to an epidemic of allergies/asthma. Author asserts this indirectly leads to cancer. Author fails to apparently take into account that although we are exposed to more male trees than female trees, our total tree (and therefore, pollen) exposure is far lower than historic norms. If adverse consequences are due to pollen over-exposure, we would still be net underexposed to pollen, so any increase in adverse health consequences couldn't be explained by that. Author also presents themselves as a "horticultural epidemiologist." Worth noting that a google scholar search suggests this person is not an academic and holds no academic credentials, but he does make his income flogging a pair of books on this topic. I guess "Epidemiologist" isn't a protected title, but I usually don't see it applied to someone that doesn't actually work in epidemiology, or hold a degree in epidemiology.

droningparrot 7y ago
One thing that isn't clear is how effective female trees are at removing pollen from the air. Is it possible that even with a much higher population but a more balanced sex ratio, there would still be a lower airborne pollen count?
- floatingatoll 7y ago
  Yes, that's the core premise made by the author: If we're going to plant male plants, either we plant female plants (which have evolved to take up the maximum amount of pollen possible) or our lungs take up the pollen (which results in biological issues). There's an inflection point where the amount of pollen left in the air by a sparse male forest equals the amount of pollen left in the air by a dense balanced-ratio forest. The article doesn't say where that inflection point is, though — when you state that inflection point as "a balanced-ratio forest can be XYZ as dense as a male-only forest with same or lower pollen counts", XYZ could be 1.1x, 20x, 5000x. Extrapolating that to urban trees, with pollen measured at human face heights, would be the holy grail of prove-or-disprove the value of this approach. It is very likely that trees evolved to pollinate no more than is necessary to deliver the correct amount of pollen to the trees near them. I cannot find any estimates of this percentage at all, so as with XYZ above, it could be 1%, 10%, or 99%. More science is definitely required in both forest-shaped configurations and urban-shaped pockets.
  - gus_massa 7y ago
    Pollen is cheap and male trees overproduce it to get an edge over other male trees. Most polen just fall to the floor, a tiny part is lucky and reach the flowers in the female trees. That's why many plants have nice flowers and use the help of insect to transport the pollen from a plant to another plant. (By the way, the yellow balls in the legs of the bees are pollen that they collect and take to the hive, for food. They "stole" most of the pollen, a small part drops in the other flower.) Also, the link in the article in the sentence "The pollen grains do not just get to the female trees by accident; rather they are drawn there by this mutual attraction." is not a good justification of that "fact".
  - im3w1l 7y ago
    I wonder how good trees really are at attracting pollen. Intuitively it sounds like the forces should be small and the effect should be pretty marginal.
    - floatingatoll 7y ago
      Trees are 0.3 billion years old, so presumably they are not just good at it, but best at it.
      - mrob 7y ago
        And birds are about 160 million years old, but they can't fly as high or as fast as airplanes. Evolution doesn't plan ahead, so it easily gets stuck in local maxima.
        floatingatoll 7y ago
        Birds seem to fall out of the sky a lot less often. Could be the same is true for pollen. I don’t know if I agree with the guy, but I think he’s right to encourage more science time and money spent on it.
        jeremysalwen 7y ago

droningparrot 7y ago

One thing that isn't clear is how effective female trees are at removing pollen from the air. Is it possible that even with a much higher population but a more balanced sex ratio, there would still be a lower airborne pollen count?

floatingatoll 7y ago
Yes, that's the core premise made by the author: If we're going to plant male plants, either we plant female plants (which have evolved to take up the maximum amount of pollen possible) or our lungs take up the pollen (which results in biological issues). There's an inflection point where the amount of pollen left in the air by a sparse male forest equals the amount of pollen left in the air by a dense balanced-ratio forest. The article doesn't say where that inflection point is, though — when you state that inflection point as "a balanced-ratio forest can be XYZ as dense as a male-only forest with same or lower pollen counts", XYZ could be 1.1x, 20x, 5000x. Extrapolating that to urban trees, with pollen measured at human face heights, would be the holy grail of prove-or-disprove the value of this approach. It is very likely that trees evolved to pollinate no more than is necessary to deliver the correct amount of pollen to the trees near them. I cannot find any estimates of this percentage at all, so as with XYZ above, it could be 1%, 10%, or 99%. More science is definitely required in both forest-shaped configurations and urban-shaped pockets.
- gus_massa 7y ago
  Pollen is cheap and male trees overproduce it to get an edge over other male trees. Most polen just fall to the floor, a tiny part is lucky and reach the flowers in the female trees. That's why many plants have nice flowers and use the help of insect to transport the pollen from a plant to another plant. (By the way, the yellow balls in the legs of the bees are pollen that they collect and take to the hive, for food. They "stole" most of the pollen, a small part drops in the other flower.) Also, the link in the article in the sentence "The pollen grains do not just get to the female trees by accident; rather they are drawn there by this mutual attraction." is not a good justification of that "fact".
- im3w1l 7y ago
  I wonder how good trees really are at attracting pollen. Intuitively it sounds like the forces should be small and the effect should be pretty marginal.
  - floatingatoll 7y ago
    Trees are 0.3 billion years old, so presumably they are not just good at it, but best at it.
    - mrob 7y ago
      And birds are about 160 million years old, but they can't fly as high or as fast as airplanes. Evolution doesn't plan ahead, so it easily gets stuck in local maxima.
      - floatingatoll 7y ago
        Birds seem to fall out of the sky a lot less often. Could be the same is true for pollen. I don’t know if I agree with the guy, but I think he’s right to encourage more science time and money spent on it.
        jeremysalwen 7y ago