Be sure to view the National Academy of Sciences and National Research Council's report on Yellowstone's Northern Range (3/26/02).

When Congress set Yellowstone's boundaries in 1872, the primary goal was preservation of the geysers and other geothermal wonders. Little thought was given to the migratory habits of its wildlife, about which little was known. The park's higher elevations provide summer range for an estimated 40,000 hoofed grazing animals (ungulates)—elk, bison, pronghorn, deer, bighorn sheep, and moose. Each year the accumulating snow of winter spurs them to lower grassland areas that are warmer and drier, where there is more open range.

Yellowstone’s largest herd of elk winter on the northern range, which covers 540 square miles along the Lamar and Yellowstone river basins, overlapping the boundary between Wyoming and Montana. A third of this area is on public and private lands north of the park.

Earlier this century it was commonly thought that the elk were "overgrazing" the northern range—eating the vegetation more quickly than it could recover and damaging the plant communities, including willow and aspen. To maintain "the right balance" between elk and their habitat, biologists believed the elk numbers had to be periodically reduced. Bison and pronghorn were also blamed for overgrazing. As a result, Yellowstone's grazers were trapped and shipped to other ranges across North America or were shot in the park. When thousands of elk were slaughtered in the 1960s, public outcry led to the reductions ceasing in 1968.

Since then, wildlife managers at Yellowstone and throughout the United States have come to recognize that populations of elk and other animals fluctuate over time, their birth and death rates affected by a combination of factors including population density, winter severity, and the quantity and quality of available food.. When the process often referred to as "natural regulation" is permitted to take place, there's no "right" number of elk for the range. Most animals are subject to hunting when they leave the park; hunters take about 10% of the elk that migrate north out of the park each year. And although it is often said that wolves were restored to Yellowstone "to restore the balance between predators and prey," this ignores the fact that other carnivores, including mountain lions, coyotes, golden eagles, and bears, have long preyed upon elk, taking up to 25% of each year’s newborn calves.

In response to continuing controversy over Yellowstone elk, in 1986 Congress ordered studies on the effects of natural regulation. This research initiative resulted in more than 40 projects by park biologists, university researchers, and scientists from other federal and state agencies, who have made substantial progress in clarifying the complex ecology of wildlands. The research demonstrates that the northern range continues to support large, healthy ungulate herds year after year, and that despite certain localized impacts, elk do not appear to have had any significant effect on the overall biodiversity of native animals and plants. Visible changes in vegetation such as a browse line on Douglas-fir stands and a lack of aspen reproduction are not simply the result of elk "overpopulation," and may be part of long-term ecological processes we are only beginning to understand. Ungrazed plants protected by research exclosures, as expected, grow taller. But except in drought years, grazing does not reduce the protein content or total volume of grass, nor does it inhibit the seedling establishment and annual growth of big sagebrush.

How can this be? Elk move across the range throughout the season, seldom grazing forbs and grasses during their most vulnerable period and generally moving to higher elevations before the plants flower and seed. Also, grazers enhance nutrient cycling by tilling the soil with their hooves and speeding up the decomposition process, converting plant matter to feces and urine that are quickly cycled back into the system. The appearance of the northern range is affected by grazing, but elk are only one of many contributing factors; the primary influence over the long term is climate and climate changes.

While it is the hope and intent of park managers that decisions will be steered by the best available scientific information, the debate over whether and how to intervene with natural systems will continue to be fueled by political processes and public pressure. Ultimately, the question of whether natural regulation is the right policy for Yellowstone is as much philosophical as scientific. The northern range provides one of the world's best laboratories for studying the complexities of landscape ecology. The park believes there is great value in preserving its components and preventing unnecessary interference with natural processes, for our future learning and appreciation. For more information write to the Yellowstone Center for Resources, P.O. Box 168, Yellowstone National Park for a copy of the 1997 report Yellowstone's Northern Range: Complexity and Change in a Wildland Ecosystem summarizing the history and research of this complex and fascinating topic.

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