The Appalachians are an old, worn-down mountain chain that runs down the eastern side of North America. The ecology of the Appalachians is fascinating. For example:
Ecologists have tested many species of Appalachian trees to see how much cold they can survive. As you’d expect, for many trees the killing temperature is just a bit colder than the lowest temperatures at the northern end of their range. That makes sense: presumably they’ve spread as far north—and as far up the mountains—as they can.
But some other trees can survive temperatures much lower than that! For example white and black spruce, aspen and balsam poplar can survive temperatures of -60° C, which is -80° F. Why is that?
One guess is that this extra hardiness is left over from the last glacial cycle, which peaked 20,000 years ago—or even previous glacial cycles. It got a lot colder then!
So, maybe these trees are native to the northern Appalachians—while others, even those occupying the same regions, have only spread there since it warmed up around 10,000 years ago. Ancient pollen shows that trees have been moving north and south with every glacial cycle.
I learned about this issue here:
• Scott Weidensaul, Mountains of the Heart: a Natural History of the Appalachians, Fulcrum Publishing, 2016.
I bought this book before a drive through the Appalachians.
To add some extra complexity to the story, David C. writes:
I’d love to understand more and reconcile that with the fact that none of these trees do well above around 4500 ft in the northern Appalachians (New Hampshire).
and Brian Hawthorne writes:
Don’t forget that all the tree species had to move back into the areas that were under the last glacier.
Trees are awesome. I’m glad I live in Minnesota where I get to watch the leaves change every fall and the leaves return every spring. I used to live in Los Angeles where it was mostly palm trees, and the only change they experience is getting taller.
I learned a couple of years ago about how aspen trees are all the above ground appearance of a single underground plant. A grove of aspens are all clones of main plant. They vary by age, but if one looks closely, one can spot that they’re all identical — same branching structure. Not at all the same as birch trees despite similar appearances.