Everyone in the United States learns about the classic cycle of the seasons in elementary school. But as the world reaches record temperatures due to heat-trapping air pollution, that cycle is being disrupted.
A 2021 study found that red maple leaves today change to their iconic fall colors a month later than they did 140 years ago — and this could have dramatic effects on forest health, National Geographic reports.
What's happening?
The changes we see in leaves in the fall are due to chemical processes inside the trees. As National Geographic explains, the green comes from chlorophyll, which captures sunlight. When the weather gets colder, trees stop making chlorophyll and reabsorb the nutrients in the leaves, revealing the yellow and orange colors behind the green. Some species, like red maples, also make red chemicals that help with absorbing nutrients.
As the weather gets hotter and this change happens later, trees have a shorter fall season. As Howard Neufeld, a biologist at Appalachian State University, told National Geographic, "The harm could come if you get a sudden freeze. The trees may not be acclimated, and the leaves may fall off before they've withdrawn all their nutrients."
Why does the changing timeline of fall matter?
For a deciduous (not evergreen) tree, losing its leaves and going dormant over the winter is sort of like going to sleep at night for a human being. It's a period of rest that's necessary so the tree can start afresh and grow rapidly in spring.
In the 2021 study, researchers Rebecca Forkner and Alexis Garretson found that modern trees that lost their leaves later than historical ones showed more signs of stress and disease, National Geographic reveals.
The long-term outcome could be disastrous. Forkner told National Geographic that it would have "consequences for the lifespan" of each tree. Some fruit trees won't produce a harvest if they don't go through this cycle correctly, too. Georgia just lost 90% of its expected peach crop that way.
Meanwhile, according to National Geographic, it's unclear whether trees under this kind of stress remove as much heat-trapping carbon from the atmosphere. It's possible that a shorter fall means we're not getting as much climate benefit from forests as we could.
What can be done about the disrupted seasons?
Cooling the Earth down by reducing heat-trapping pollution is the No. 1 way we can restore a more natural climate. That requires working together to make eco-friendly policy changes while also supporting them with individual choices like switching to electric cars and appliances instead of gas.
Neufeld suggested, "If more people get out and see nature and appreciate its fragility, they might be more conducive to doing something to protect nature."
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