On Dunes


Saltation
"[T]he real dune-building action happens within inches of the ground. Even in a modest offshore wind, sand grains moving on the beach either roll and ripple along in a movement pattern called surface creep or actually play a kind of micro-geologic hopscotch called saltation, tiny grains slamming hard enough into a sequence of downwind neighbors to send them bounding into the air."


Hidden Webwork
"Here, as in other coastal dune systems, a single blade of marram grass---or any of a handful of other colonizers---can begin the building of a giant. A tiny mound of blowing sand collects around the obstruction. More and more sand collects on the back side of the tiny mound, interrupting the force of wind enough for still more sand to drop out, until a ridge forms in a classic dune-ish shape: a long slope on the windward side, a steepdrop on the lee. In time beach grasses wil thoroughly colonize the new dune, stabilizing it with a webwork of roots and rhizomes."


Diversity
"The Indiana Dunes National Lakeshore is the most fragmented unit in all the national park system, its protected patches broken by housing and industrial development. At just over 14,000 acres, it is a tiny national park, compared with placed like the Everglades (1.5 million acres) or Yellowstone (2.2 million acres). Yet the dune park harbors more total biological diversity than all but three national parks, and by far the highest plant diversity per acre. Here you can find arctic bear-berry hundreds of miles south of its usual boreal range, growing within feet of prickly pear cactus; you can find southern dogwood just over a rise from jack pine, normally a tree of the far-north woods."

A classic article on dunes
Henry Chandler Cowles, "The Ecological Relationships of the Vegetations of the Sand Dunes of Lake Michigan" [1899].

Cowles studied the succession of plant communities, to climax forests, and first got the idea from hiking dunes and observing the changing plant communities. His study is the first example in America of the science of ecology, building on an idea that had been circulating among some contemporary European scientists that posited that ecosystems could change and evolve as species could. Cowles' was the first study to put these ideas to the test, with a detailed study of communities of plants and animals interacting in a specific environment over time.

On the Origins of the Name for Sleeping Bear Dune

"The Potawatomi, the Native American nation in the area that later became the state of Michigan, are the source for the 'sleeping bear' legend about the origin of the Manitou Islands that gave Sleeping Bear National Park in Michigan its name."

The tale as I remember it (I heard it as a child): One time on the other side of the lake, in the land now called Wisconsin, a huge forest fire raged. A mother bear gathered her two cubs together and set out with them to swim to safety across the lake. It was a long swim. After swimming for many hours the family came in sight the other shore. But the baby bears began tiring. They could go no more. The mother bear urged them to keep swimming. But they couldn't. She tried to push them and help them swim herself but she wasn't able to; she could barely keep swimming herself. The mother finally crawled ashore and feel asleep from exhaustion at the edge of the beach. In the morning she awoke and looked out over the water. She saw the backs of her two cubs sticking above the water. In her fear and her grief she couldn't let herself believe what had happened. She told herself that her cubs were just sleeping, just storing up energy for the last push to shore. She told herself that if she went back to sleep herself when she waked up her cubs would be with her again.

That is why there are two islands offshore and a huge dune watching over them.

All info from John R. Luoma, "Restless Dunes," Audubon Magazine, Nov./Dec. 1994: 78-89 (quoted and paraphrased).

Headings in bold not in Luoma, and the retelling of the Potawatomi story is my own, elaborated from the basic story I remember from childhood.



"The extraordinary biodiversity in rainforests and coral reefs is due in part to their complicated 'structure'---multilayered intermingling of micro-habitats. While old-fashioned shaded coffee farms [in Central America] are not as layered as natural forest, they offer much more structure than most crops---and surely more than coffee fields planted in full sun or even in groves of Inga trees."

Chris Wille, "The Birds and the Beans," Audubon Magazine, Nov./Dec. 1994: 62.




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