A Tribute to Dune Succession
It’s autumn. And a yellow Eastern cottonwood tree stood far in the distance, made evermore golden and bright by a spotlight of sun and the dark backdrop of a shadowy dune.
Little did I know, I was standing at the epicenter of the study of ecological succession and, more specifically, dune succession—along the Cowles Bog Trail, named after Henry Chandler Cowles for his groundbreaking research on the topic. The dunes of this national-park are the Birthplace of American Ecology.
The image was made on a foredune near the Michigan shoreline, not long after Zeke and I bounded down a high, steep dune (upper right in the photo) through powdery sand that supposedly “sings” when walked upon. We spotted that tree just after we landed. My photographer friend headed straight for it. I decided to stay back to appreciate and photograph the soft highlights and long, gentle shadows of a low sun, known for accentuating ephemeral shapes in the sand and the individual plants that make up any habitat.
Do you see those saplings of golden-leaved cottonwood in the foreground, mixed in with marram grass? Together, they make the perfect tribute to that dazzling distant tree and the building of the dunes through a few-thousand-year process known as dune succession. Nutrient-barren sand is transformed into a sea of grass, flowers, shrubs, sand-loving trees, like cottonwoods and black oaks, and, most remarkably, the towering dunes like the one I most recently plunged.
The currents and waves of Lake Michigan deposit barren grains of sand on the shoreline to create a lifeless beach. As sand is washed and blown inland, it is trapped by plants that, over time, form a foredune—a long, narrow mound that runs parallel to the beach.
The main collector of sand is marram grass, which is able to survive the brutal elements and a soil devoid of nutrients. It does this, in part, thanks to a rootlike structure of rhizomes, a type of stem that collects and stores nutrients while also spreading out horizontally to sprout more plants. This net of rhizomes can spread as wide as twenty feet to moor the wandering sand. Each winter, its foliage decays to the ground to further nourish the sand that, over time, becomes rich enough to support other plant species which, in turn, repeat the same pattern. Each new plant stabilizes the soil and amasses more sand, eventually supplanting and occupying the role of marram grass. The cycle continues until nutrient-hungry trees take hold atop towering dunes of sand.
Thanks to marram grass, we have our mighty dunes.
—Mike