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Nov. 06, 2012

The Plant That Ran with Buffalo

by Kara Rogers

Click to enlarge images
Running buffalo clover produces a single, spiked flower, one that is quintessentially clover. But unlike other clovers, running buffalo is endangered -- it was once even thought to be extinct, for reasons that are reflected in its name. Indeed, in its native habitat in North America's Appalachian and Bluegrass regions, it ran with the bison, growing alongside the paths the animals trampled and in the fields they grazed. But that was before bison were hunted to extinction in those areas.

The decline of running buffalo clover (Trifolium stoloniferum) is linked inextricably to the larger history of European settlement in the Appalachian region of Ohio, West Virginia, and Kentucky and in the latter's Bluegrass region. As European settlers moved into those areas, tribes of Native Americans, including the Shawnee, Chickasaw, Cherokee, and Yuchi, moved out (in many cases, they were forced out). Land was converted for agriculture and was seeded with grasses ideal for livestock grazing, including bluegrass (Poa pratensis) and timothy grass (Phleum pretense). And there was an alarmingly swift decline in populations of large game animals, including deer, elk, and bison. Bison were hunted so intensely that they were extinct locally by 1800, eight years after Kentucky gained statehood.
 
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The American bison (Bison bison), because of its size and sheer number, was a destructive animal, trampling vegetation and tearing up soil. But it was exactly this disturbance that biologists suspect enabled the running buffalo clover to thrive. In eating the plants, the bison helped to disperse the clover's seeds. And the packed soil of the bison's wallows and the rough ground of its traces (migratory paths) limited the growth of trees, resulting in sparsely wooded habitat with just the right amount of shade and sun for running buffalo clover. Also, lacking Rhizobium bacteria, which convert nitrogen into ammonia and other compounds used by leguminous plants like clover, running buffalo likely acquired nitrogenous nutrients directly from bison manure.

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Like other types of clover, running buffalo has leaves divided into three leaflets, and it grows runners, or stolons, that extend laterally from the stem. Stolons frequently become buried beneath the soil, where nodes along its length grow roots and give rise to new plants, all genetically identical. Stolons may facilitate nutrient sharing between individual plants, allowing them to more efficiently use resources in disturbed habitats. But because each plant is a clone, a single population of clover, particularly a small population, typically has a low level of genetic diversity. This in turn could limit the plant's ability to adapt readily to major ecological change -- such as the relatively sudden loss of bison.

Other factors that are thought to have played a role in the running buffalo clover's decline include habitat loss, the introduction of invasive species, and changes in land management that facilitated ecological succession in formerly open woodlands. As a result, overcoming these factors is key to the species' restoration. And while there is much to be hopeful for, given the species’ rediscovery in 1985 and the continued discovery of new populations, its presence will be forever haunted by the ghost of the great animal that once dominated its habitat.
About Kara Rogers

Kara is a freelance science writer and senior editor of biomedical sciences at Encyclopaedia Britannica, Inc. She is the author of Out of Nature: Why Drugs From Plants Matter to the Future of Humanity (University of Arizona Press, 2012).

The views expressed are those of the author and are not necessarily those of Science Friday.

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