Trees on the Move

Birds are doing it, now trees are too.

All over the world, trees are moving to new places to escape warmer temperatures. They are taking root at higher elevations as well. But this isn’t happening in response to hot summer temperatures: warmer WINTER temperatures are the cause.

In BBC News, Matt Walker quotes biologist Melanie Harsch as saying, “We expected growing season warming to be the dominant driver, but we found that it was not, winter temperature was.”

Walking outdoors in the fall in Europe, you can enjoy the lovely yellow leaves, while the US and East Asia, the turning leaves are mostly red. What causes the differences in autumn leaves around the world? The answer goes back 35 million years.

The green of a tree’s leaves is from the larger proportion of the chlorophyll pigment in the leaves. The change in color to red or yellow as autumn approaches is not the result of the leaves’ dying, but of a series of processes, which differ between the red and yellow autumn leaves. When the green chlorophyll in leaves diminishes, the yellow pigments that already exist become dominant and give their color to the leaves.

But red autumn leaves result from a different process: As the chlorophyll diminishes, a red pigment which was not previously present, is produced in the leaf. So why do some trees create red pigments just as they are about to shed their leaves?

An evolutionary approach theorizes that the strong autumn colors result from the long war between the trees and the insects that use them as hosts. During the fall season, which is when the insects suck the amino acids from the leaves and later lay their eggs, a tree that is vulnerable to these attacks colors its leaves in red because aphids are attracted to yellow leaves. Yellow leaves are predominant in parts of the world that do not have these insects.

Let’s hope we figure out what’s going on with our trees before it’s too late to save them! And let’s hope more of our readers and listeners start supporting this website (and our great radio shows) before it’s too late to save US! You can keep us going for less than a latte a WEEK: Less than $12 gets you a 3-month subscription. So what are you waiting for? Subscribe today. And come on out and starwatch with us in the desert in October!

Art credit: Dreamstime.com

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