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Next year will mark the 100th anniversary of the publication of a series of scientific papers under the general title "The Ecological Relations of the Vegetation on the Sand Dunes of Lake Michigan." Written by Dr. Henry Chandler Cowles of the University of Chicago, the papers were a major contribution to the young science of ecology, a major shaper of what we now think of as the commonsense view of the structure and functioning of natural communities.

The story that has been handed down says that Cowles got interested in the dunes while on his way to Chicago to take up his position at the university. His train stopped somewhere in northwestern Indiana, and he became intrigued by plants he could see growing near the tracks. His subsequent investigations centered on the Indiana Dunes but also extended up the Michigan shore of the lake to Sleeping Bear Dunes and beyond.

The naturalists of the 17th and 18th centuries studied a world they considered quite young. There was creation, the catastrophe of the Noachian flood, and ever since things had been pretty quiet. All species were created in the beginning, and one of the satisfactions of the study of nature was discovering how beautifully individual species fit into their environments.

The 19th century brought time and change into the picture. Geologists kept increasing their estimates of the age of the earth. Fossils came to be understood as records of plants and animals that had once thrived but were now extinct. Darwin and others showed how new species could be created by the interactions between organisms and their environment.

As Cowles studied the flora of the dunes, he came to realize that a walk through the dunes was a walk through time as well as space. By studying the vegetation of the contemporary dunes, he could decipher the history of the place.

"The ecologist," he wrote, regards, "the flora of a pond or swamp or hillside not as a changeless landscape feature, but rather as a panorama, never twice alike. The ecologist, then, must study the order of succession of the plant societies in the development of a region, and he must endeavor to discover the laws which govern the panoramic changes. Ecology, therefore, is a study in dynamics. For its most ready application, plants should be found whose tissues and organs are actually changing at the present time in response to varying conditions. Plant formations should be found which are rapidly passing into other types by reason of a changing environment."

At the dunes Cowles found perfect examples of plant formations "rapidly passing into other types." The basis for the change was the extreme youth of the landscape. Our whole region was under ice until 14,000 years ago, and much of the land near the present shore of Lake Michigan was underwater until only 4,000 years ago. The history of the lake's retreat to its present size is written in a series of beach ridges that curve around the southern shore. The oldest of these ridges are as much as ten miles inland. Depending on the slope of the terrain, the youngest ridges may be only a few hundred yards from the present shore.

The vegetation of the present-day beaches is quite sparse. On the lower beaches, where the waves of summer storms regularly disrupt things, no plants grow. On the upper beach, where only the more violent storms of winter strike, a few scattered annuals can survive. Yet on old beach ridges just a short distance inland, forests thrive. Cowles recognized that the beach environment is a difficult one. On the Indiana shore winds sweep across the water before striking the land with immense force. Cowles recommended that people lie on the sand facing into the wind to get a real sense of how much sand is landing on the beaches. You can follow his advice today. The beach environment is subjected to a nearly continuous low-level sandblasting, an onslaught only the most thick-hided plants can survive.

Half a mile inland conditions are much more benign. Cowles's own research highlighted the contribution of the plants themselves to this more comfortable situation. You can study an example of this contribution at Montrose Beach. In 1994 an Illinois endangered species called sea rocket was found growing on the beach. The plant is a thick-skinned annual that specializes in life just above the summer-storm line. The Park District erected a fence around the plant, and ever since the fence has protected a small piece of the beach from human disturbance. Cottonwoods in great numbers have invaded the protected space. These are true dune builders. Their roots and trunks capture blowing sand and hold it near them. If the sand around them grows too deep, the trunks can sprout new roots.

Cowles noted the importance of cottonwoods, marram grass, and a few other pioneering plants as builders of dunes. The sand piles up around them. The plants grow new roots to stay above the deepening sand, and eventually you have dunes nearly 200 feet above the waterline. These dunes grow only along the southeastern and eastern shores of the lake. Prevailing northwesterly winds carry the sand to these shores. On the lake's eastern shore the dunes are low. The lake deposits sand along the shore, but the winds do not carry it inland.

In the lee of every high dune is a sheltered space, a low spot that the winds seldom reach. Here wetland plants less specialized for life on the windy dunes can find a home, and woodland and prairie species can thrive.

At every step in this process, Cowles discovered, the plants are active agents in the changes taking place. Their roots help stabilize the sand. Their shade moderates the shifts between hot and cold, between wet and dry. Their decomposing remains enrich the soil, turning sterile sand into fertile ground.

I visited Indiana Dunes State Park twice last month and was reminded of how strongly Cowles's research influences my view of the landscape. Walking the trails between the nature center and the beach, I stepped through every stage from sugar maple to marram grass. The dunes near the beach were cold and windswept. The bark of an ironwood tree growing on the foredune had been bleached from brown to gray by the wind. In the basins and on the slopes of the high dunes that have been built in the 4,000 years since the lake receded, sugar maples and basswoods grew under a canopy of oaks. Witch hazel, sassafras, and flowering dogwood formed a dense shrub layer. On the crests of the high dunes, where conditions were drier and windier, black oaks dominated the landscape and blueberries covered the ground under the shade of the oaks.

Cowles taught us to see these differences as moments in time. We should expect change, and if we study the landscape carefully we can predict the likely direction of that change. If things are not changing, there is a reason. Some forces are pushing the land in the direction of stability, and we can study those.

One of Cowles's students at the University of Chicago was May Thielgaard Watts. She popularized the work of Cowles and others in the fledgling science of ecology. Through a series of books with the general title of "Reading the Landscape" and through generations of classes at the Morton Arboretum, she taught laypeople that landscapes are ordered in both space and time. She taught that we can understand what is happening in these landscapes if we study their history and learn to interpret their present state as the product of that history.

Ray Schulenberg, who planted the first prairie restoration in Illinois at the Morton Arboretum, and Floyd Swink, senior author of the best book on regional flora in North America and a superb educator, both learned from May Watts. They in turn educated the educators who are working as naturalists in the local forest preserves, planning exhibits at local zoos and museums, and creating curricula for local schools. Cowles's insights guide land managers responsible for sustaining natural communities in parks and preserves. They have become local traditions, like 16-inch softball. His work, completed 100 years ago, is still helping protect our remaining natural communities.

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