One of those ways creates quite a bit of suffering for humans: pollen, the infamous male gametophyte of the plant kingdom
Evolution has fostered many
reproductive strategies across the spectrum of life. From dandelions to
giraffes, nature finds a way.
One of those ways creates
quite a bit of suffering for humans: pollen, the infamous male gametophyte of
the plant kingdom.
In the Southeastern US, where
I live, you know it's spring when your car has turned yellow and pollen
blankets your patio furniture and anything else left outside. Suddenly there
are long lines at every car wash in town.
Even people who aren't
allergic to pollen – clearly an advantage for a pollination ecologist like me –
can experience sneezing and watery eyes during the release of tree pollen each
spring. Enough particulate matter in the air will irritate just about anyone,
even if your immune system does not launch an all-out attack.
So, why is there so much
pollen? And why does it seem to be getting worse?
2 ways trees spread
their pollen
Trees don't have an easy time
in the reproductive game. As a tree, you have two options to disperse your
pollen.
Option 1: Employ an agent,
such as a butterfly or bee, that can carry your pollen to another plant of the
same species.
The downside of this option
is that you must invest in a showy flower display and a sweet scent to
advertise yourself, and sugary nectar to pay your agent for its services.
Option 2, the budget option,
is much less precise: Get a free ride on the wind.
Wind was the original
pollinator, evolving long before animal-mediated pollination. Wind doesn't
require a showy flower nor a nectar reward. What it does require for
pollination to succeed is ample amounts of lightweight, small-diameter pollen.
Why wind-blown pollen makes
allergies worse Wind is not an efficient pollinator, however. The probability
of one pollen grain landing in the right location – the stigma or ovule of
another plant of the same species – is infinitesimally small.
Therefore, wind-pollinated
trees must compensate for this inefficiency by producing copious amounts of
pollen, and it must be light enough to be carried.
For allergy sufferers, that
can mean air filled with microscopic pollen grains that can get into your eyes,
throat and lungs, sneak in through window screens and convince your immune
system that you've inhaled a dangerous intruder.
Plants relying on
animal-mediated pollination, by contrast, can produce heavier and stickier
pollen to adhere to the body of an insect. So don't blame the bees for your
allergies – it's really the wind.
Climate change has a role
here, too
Plants initiate pollen
release based on a few factors, including temperature and light cues. Many of
our temperate tree species respond to cues that signal the beginning of spring,
including warmer temperatures.
Studies have found that
pollen seasons have intensified in the past three decades as the climate has
warmed. One study that examined 60 location across North America found pollen
seasons expanded by an average of 20 days from 1990 to 2018 and pollen
concentrations increased by 21%.
That's not all. Increasing
carbon dioxide levels may also be driving increases in the quantity of tree
pollen produced.
Why the Southeast
gets socked
What could make this
pollen boost even worse?
For the Southeastern U.S. in
particular, strong windstorms are becoming more common and more intense - and
not just hurricanes.
Anyone who has lived in the
Southeast for the past couple of decades has likely noticed this. The region
has more tornado warnings, more severe thunderstorms, more power outages. This
is especially true in the mid-South, from Mississippi to Alabama.
Since wind is the vector of
airborne pollen, windier conditions can also make allergies worse. Pollen
remains airborne for longer on windy days, and it travels farther.
To make matters worse,
increasing storm activity may be doing more than just transporting pollen.
Storms can also break apart pollen grains, creating smaller particles that can
penetrate deeper into the lungs.
Many allergy sufferers may
notice worsening allergies during storms.
The peak of spring wind and
storm season tends to correspond to the timing of the release of tree pollen
that blankets our world in yellow. The effects of climate change, including
longer pollen seasons and more pollen released, and corresponding shifts in
windy days and storm severity are helping to create the perfect pollen storm.
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