Top: An ornery bull poses by a fire hydrant in Mammoth Hot Springs. This one charged a number of people that made the mistake of moving in too closely while snapping pictures. This shot was taken with a 400 mm lens - a safe length for wildlife photography in Yellowstone.

From the Northern Range Newsletter: "When concern about overgrazing first surfaced in the 1920s, opinions on how the Northern Range "should" look were based on the only available criteria: that used to evaluate ranges grazed by domestic livestock. Scientists had no clear idea of how unmanipulated wildland grazing systems worked or what they typically looked like because by that time they were already gone in the United States, often replaced by domestic livestock operations which have entirely different goals and effects on the landscape. But wildlife are not livestock, which move primarily when and where humans move them. Wild ungulates have evolved with their range, which has adapted to survive their grazing.

Consequently, a wildland range does look different from a commercial range; its appearance depends entirely on environmental factors, instead of on close supervision by someone whose primary goal is to maintain the highest sustainable level of livestock production. What a wildland ecologist would consider normal grazing effects, a livestock manager might consider unacceptable. For example, ranchers view evidence of erosion with alarm because soil is an economic asset. But in a wildland area where natural processes are to function as much as possible without human interference or economic considerations, erosion is an inherent part of the landscape, whether caused by the movement of animals or long-term geological forces.

Instead of assessing a range based on its appearance, scientific appraisals of both commercial and wildland ranges depend on the measurement of criteria such as plant productivity. In Northern Range research, these evaluations have been done by comparing grazed areas to areas inside plots that have been fenced to prevent grazing.

Although plants on ungrazed plots are taller, research on the Northern Range has shown that, except in drought years, grazing does not reduce the seasonal protein content or volume of grass, or the seedling establishment or growth of big sagebrush.

How can this be? Elk move across the range as foraging conditions dictate, seldom grazing forbs and grasses during their most vulnerable period and generally moving to higher elevations before the plants flower and seed. In addition, the effect of processing plants through an ungulate's digestive tract is very different from plants being left to die as leaves and stems on the ground. Grazers enhance the cycling of nutrients by tilling the soil with their hooves and by speeding up the decomposition process, converting plant matter to feces and urine that are quickly cycled back into the system along with their own carcasses.

The appearance of the Northern Range is affected by grazing, but ungulates are only one of many contributing factors; the primary influence over the long term is climate.

Research has shown that about 83% of the elk's winter diet comes from grasses and forbs, the rest from woody vegetation. Although some observers have attributed a decline in willows and aspen on the Northern Range to overbrowsing by elk, other factors may be involved. Where willows grow in Yellowstone is almost entirely determined by altitude and precipitation: 99% of the park's willow communities are found in areas that are above 7,000 feet and/or receive more than 20 inches of annual precipitation, which excludes most of the Northern Range. Although old photos show that some Northern Range locations had much taller willows in the 1890s than they do now, most of the decline in the last century has been during droughts rather than periods of large elk populations. No significant decline in Northern Range willows has occurred since 1959 despite a quadrupling of elk numbers.

Like willows, aspen thrive in areas of the park where the climate is better suited to them, including ungulate summer ranges and other places that receive more than 25 inches of precipitation a year. A 1995 tree-ring study showed there's been only one period since the early 1800s when Northern Range aspen were able to escape browsing and reach tree height. Most of the aspen that are growing old on the Northern Range now were just getting started during the period from the 1870s to the 1890s.

While this evidence suggests that the sparseness of Northern Range's willows and aspens cannot be explained simply by the size of the elk population, its woody vegetation has been studied far less than its grasses and sagebrush. The park strongly supports the need for more research on the relationship of willows and aspen to other plants and animals on the range."

Below: A bull in velvet chews away at the abundant greens of spring on the Blacktail Plateau in northern Yellowstone.