Forests Reveal Lingering Effects of Native Cultures

The distribution of trees found in the forests of the Eastern United States may reflect Native American agriculture more than habitat.

Robert J. Warren, assistant professor of biology, shows that the distribution of Gleditsia triacanthos (honey locust) throughout the southern Appalachian Mountain region in the United States can be best explained by ancient cultivation practices of the Cherokee.

“Native Americans may have affected the concentration of plant species long before Europeans came to North America,” said Warren. “The purpose of this research was to test the hypothesis that a centuries-old legacy of Cherokee cultivation explains current regional G. triacanthos distribution patterns.” Warren described his findings in Ghosts of Cultivation Past: Native American dispersal legacy persists in tree distribution, published in PLOS ONE in March.

Warren began his surveys and field experiments, including seedling introductions, in 2009. “I always have an underlying interest in the patterning of plant species,” he said. “While I was doing field work in Southern Appalachia, I noticed that whenever I saw a honey locust, I could throw a rock and hit a Cherokee archeological site. I knew that, in the late Pleistocene era, the main source of dispersal for honey locusts was megafauna such as mastodons. But mastodons disappeared more than 10,000 years ago. You’d expect plant species that relied strictly on extinct megafauna for seed dispersal would only exist in small, remnant populations.”

Several theories regarding the persistence of G. triacanthos include dispersal by smaller animals such as white-tailed deer; livestock introduced by European settlers; and water transport. However, Warren—whose research focuses on biotic dispersal of plant seeds leading to plant distribution—decided to investigate further.

“When we look at distribution of plant species,” he said, “ecologists are accustomed to assume that plants thrive in habitats with abiotic characteristics—water, sunlight, soil type— that meet the plants’ needs. Questioning that assumption leads to interesting discoveries.” Warren explores mutualism between biotic (living) organisms such as insects and the plants that depend on them. In Ghosts of cultivation past, he notes that “…some plant distributions better reflect the niche requirements of the mutualist than the plant itself.”

He points out that the Cherokee had reason to cultivate the honey locust as a source of sugar, and as wood for game sticks and weapons. The tree also had spiritual significance. He conducted extensive searches for honey locust trees and then used sources including military maps, historical accounts, archeological research, and historical markers to identify Cherokee settlement sites. He verified the information with sources including the Eastern Band of the Cherokee Nation (EBCI) Tribal Historic Preservation Office. His results strongly suggest that G. triacanthos distribution in the Southern Appalachian region is more strongly patterned by Native American settlements than by niche requirements or alternative methods of seed dispersal.

Warren said that the same may be true for other trees, including paw paws and the Kentucky coffee tree, and probably many others. “Native Americans of North America were shaping their environment long before the colonial period,” said Warren. “Instead of pyramids and temples, they left their mark in the ecosystem they helped to create.”