Henry Chandler Cowles (1869-1939) was a University of Chicago botany professor and conservationist. His studies of plant life in the Indiana Dunes made Cowles one of America's most notable early ecologists.
Cowles was born on February 27, 1869, in Kensington, Connecticut. His love of nature started when he was a child. His mother taught him the names of flowers and trees on their walks together, and he raised flowers and vegetables on the family farm.
Cowles earned a degree from Oberlin College in 1893 and spent a year as a natural science teacher at Gates College in Nebraska before arriving at the University of Chicago as a graduate student in 1895.
Ecology in the 1890s was a relatively new area of study. German zoologist Ernst Haeckel coined the word “ecology” in 1866. In addition to this new scientific field, Charles Darwin's On the Origin of Species (1859) and Charles Lyell's Principles of Geology (1830-1833) were causing scientists to think about the relationships between animals, plants, and their environment in new ways.
In 1896, Cowles traveled to the southern shore of Lake Michigan to see the Indiana Dunes for the first time.
Sand dunes are formed when grains of sand are blown by the wind into mounds or ridges. Dunes are among the least stable landforms on Earth. Because changes to the dune ecology happen so fast, plants must adapt quickly to a new environment, Cowles noted.
Plants “are obliged to adapt themselves to a new mode of life within years rather than centuries, the penalty for lack of adaptation being certain death," said Cowles.
For an ecologist, the dunes around Indiana’s Lake County and Porter County were an ideal laboratory for studying the relationships between plants and their environment.
Cowles traveled back and forth from Illinois to northwest Indiana to observe the dunes in all seasons. He saw that dunes moved steadily away from the shore due to wave action and the westerly winds blowing across Lake Michigan.
As he walked farther inland, Cowles noticed that different types of plants grew in the sand dunes. The sand dunes closest to the beach only supported the hardiest plants, such as marram and sand reed grasses. When these plants died, the decomposing matter created conditions favorable to other types of plants, such as bladderworts and cottonwood trees. More plants, roots, and rotting plant matter led to an even greater variety of plants, like juniper bushes and pine trees.
Plant Succession and Climax Formation
Between 1899 and 1901, Cowles published three landmark papers. He observed that the shape of the land, or topography, and the type of soil have an enormous influence on the type of plants that grew there. These findings introduced ecologists to two important ideas: plant succession and climax formation.
In plant succession, one plant community will create the conditions ideal for other plants to replace, or succeed, it. Every stage of plant succession is more stable than the one that came before.
"Each species affects the soil in a way disadvantageous to itself and thus paves the way for different species to replace it," said Cowles.
This process of plant succession led to Cowles' second important theory: climax formation. A climax formation is the most stable plant community created by plant succession. All plant successions are headed toward the establishment of a climax formation.
A climax formation will stay the same unless something destroys the plants or changes the shape of the land. Forest fires and human activity can change the shape of the land. Plant succession will usually start all over again, ultimately leading to a climax formation.
In the dunes, the climax formation is an oak forest. The sand dunes near the beach give way to beach grasses, which give way to cottonwood trees, which give way to pine trees. Ultimately, pine trees give way to an oak forest.
Cowles compared the plants from the Lake Michigan dunes with plants from dunes in the Chicago area. Then, he compared these dunes with dunes in Connecticut, Montana, northern Michigan, and Tennessee. The climax formation pattern was the same in all dune ecosystems.
The Botanical Gazette published Cowles' PhD thesis, "The Ecological Relations of the Vegetation on the Sand Dunes of Lake Michigan," in 1899.
After 1901, Cowles concentrated on teaching at the University of Chicago, where he spent the next 30 years. His best-known class was a course called Botany 36. Groups of 15 students visited Lake Michigan, Lake Superior, and Lake Huron. Some classes traveled as far as California, Oregon, Washington, and British Columbia, Canada, to study local plant communities.
In 1913, Cowles led a group of German scientists on an ecological tour of the United States. Cowles said, "As there was so much to see in the brief time that we had to see it in, I asked these people who had come here to indicate what they wanted to see in the United States in two months. There were three or four things that all of them mentioned as highly worth seeing, even in the briefest trip to the United States. They were the Grand Canyon, Yosemite, Yellowstone Park, and the fourth was the Lake Michigan dunes."
The Ecological Society of America (ESA) was a result of the 1913 meeting. An offshoot of the ESA later became the Nature Conservancy. Today, the Nature Conservancy is a nonprofit organization dedicated to preserving wildernesses and natural habitats.
After World War I, an Indiana state park was established in Cowles’ honor. On December 2, 1965, 56 acres of Porter County, Indiana, were designated Cowles Bog National Natural Landmark. Congress authorized the creation of Indiana Dunes National Lakeshore in 1966.