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Window on a Vanished World
| Article
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21910 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
7 / 1993 |
1,480 Words |
| Author
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Mary Meagher And Linda Wallace
Mary Meagher is a research biologist with the National Park Service and has studied the bison in Yellowstone National Park for over 30 years. Linda Wallace is an ecologist at the University of Oklahoma, specializing in ungulate-grass interactions. She has studied bison grazing influences on forage plant growth and ecosystem processes since 1981. |
The early morning mist lifts slowly. Through the golden dawn, an enormous, shaggy, dark form appears, followed by another and another. Gradually, a whole majestic herd of grazing bison comes into view.
Most people can easily envision a mystical scene of a massive bison herd thundering across the Great Plains, such as in Dances with Wolves. But that romantic scene is not the reality of most bison herds today in two ways. First of all, present-day bison are generally managed like, and are often equated with, cattle, either consciously or unconsciously. However large the refuge, reserve, or ranch, they are surrounded and dissected with fences. The result is that while bison as a species have rebounded from the near-extermination a century ago, their life has changed forever.
Secondly, if any image is most representative of the bison it is not a stampede, but a calm, persistent foraging of the land. Individually they forage as huge and somewhat indiscriminate mowing machines, taking large quantities of relatively low food-quality grasses and sedges. In large aggregations, they graze a site intensively, but briefly, and then move on. In Yellowstone National Park, they may return to a given site after a few weeks, but on the Great Plains the time they took to return may have been longer. Historic accounts describe vast herds, far larger than those of Yellowstone, but there were likely great expanses vacant at the same time, having been grazed earlier.
The plants the bison forage appear to have evolved with this intense but brief exploitation, and regrow rapidly in response to grazing. Ever notice how suburban lawns seem to grow faster after mowing? Forage species used by bison respond in the same way. Thus, when the bison return to graze again, the plants are ready.
To get a glimpse of the true world of bison, some scientists think it is important to maintain herds whose group behavior and population structure are not manipulated by humans. Such is the situation at Yellowstone, which is one of the few places where bison are truly free-ranging, primarily due to the park's vastness and the fact that the herd's numbers are not managed within predetermined limits. Managed thus, and free to move as they choose, they have done what any population will do: They have fully occupied suitable park habitat, and are looking for additional, vacant (at least to a bison) lands to occupy, sometimes to the chagrin of landowners at the park's perimeter.
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