Natural Connections: Glacial Refugia

Cade Campbell is from Bristol, Tennessee, and is currently studying Biology at East Tennessee State University. An avid naturalist, he spends most of his free time outdoors, and has both worked and volunteered with the Blue Ridge Discovery Center as a naturalist, and as a field technician elsewhere. Cade just finished his tenure as a Summer Naturalist Intern at the Cable Natural History Museum.

Lush hemlock boughs with tiny, thimble-sized cones wavered in the gentle breeze as I strolled along the crunchy gravel road behind the Forest Lodge Nature Trail. On the ground, familiar friends like wild sarsaparilla, Mayflower, and moccasin-flower were unleashing their vernal beauty. It felt like an evening back home in the Southern Appalachian Mountains. These are fragments of plant communities I know intimately from Appalachia, over a thousand miles away from Northwest Wisconsin to the south.

So why are they here?

During the last glacial period (which ended around 11,000 years ago), the inescapable Laurentide Ice Sheet wiped out all life in its path. Some northern inhabitants made their way south, beyond the ice. The mighty Appalachian Mountains, once the tallest mountains ever to exist on the planet, provided a suitable place where these northern plants, animals, and fungi could survive alongside southern counterparts in protected valleys and ridges. The Southern Appalachian Mountains became a “glacial refugium.”

“The mountains have provided a fortress: support and strength to survive” wrote Helen Matthews Lewis, the great Appalachian sociologist and activist, in her poem “Redbud Trees.” Without Lewis’ proverbial “safe place,” much of the beloved life now and formerly indigenous to the Northwoods would not have survived the last ice age. When the glaciers receded, plants, animals and all life spread back across the scoured continent from the mountains and other unglaciated areas. The confluence of two ecosystems prevented the last ice age from exterminating the species we know and love in the Northwoods today.

As I continued ambling down Lost Land Lake Road, starflowers and bunchberries illuminated the mossy knolls. The overwhelming fragrance of sweetfern, the satisfyingly curly sheets of peeling paper birch bark, and the lonesome spires of black spruce indicated that this was a very different place than the distant mountains. These plants survived glaciation in the Appalachian Mountains, but none of them grow in Southern Appalachia anymore.

Some northern and southern species are still mingling on high-elevation peaks in Appalachia, as the climate and habitats change. Black bears, ruffed grouse, and trillium are equally at home in both the Northwoods and the Appalachian Mountains, despite regional eccentricities. Bears do not spend the winter hibernating in most of the Southern Blue Ridge Mountains, and nodding trilliums have diverged into slightly different species. Genetically, they remain long-lost relatives.

Many more species, now common in the north, have been transformed into rarities by time and climate, stranded on cooler, wetter “islands in the sky” in Appalachian refugia. Black-capped chickadees, wood lilies, and any kind of spruce or fir trees are familiar friends in the Northwoods, but increasingly rare in much of Appalachia.

While leading a Junior Naturalist program for the Museum this summer, I watched a snowshoe hare creep from the woods mere feet away from our group. I was just as excited as the kids, if not more! Later, while driving at dusk, I straddled multiple hares with my car as they bolted across the road. Amazingly, none were harmed. But even if I’d run one over, there are plenty of hares deeper in the forest.

In contrast, snowshoe hares were likely extirpated from the southern mountaintops during my lifetime; the climate can no longer support them. They are just one of the species who have disappeared entirely. With each missing member, the health of the ecosystem is drastically weakened.

Where species once migrated south to escape a wall of ice, they must now escape in the opposite direction to avoid excessive heat. My beloved Appalachians are being inundated by wildlife from much farther south. Locations with habitat similar to the Northwoods mere decades ago host life more reminiscent of habitats in the coastal Carolinas or Georgia. Cold-adapted species are forced north or to an untimely local extinction.

This means the Northwoods are receiving new waves of southern species, from great crested flycatchers to swamp darner dragonflies…and for a short time, me. As I prepare for my own migration back south after a summer in the Northwoods, I’m saying goodbye to spruce and fir, black-capped chickadees, and the scarlet clusters of bunchberries. To the wild sarsaparilla, Mayflower, and moccasin-flower I can just say, “I’ll see you at home.” …At least for now.

Millennia after glaciation, the Northwoods of Wisconsin have become a refugium for species trying to survive a modern climate. Only time will tell if life is able to survive heat as well as it escaped ice.

For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is now open with our exciting Growing Up WILD exhibit. Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.