Dimension of Elk Management in Yellowstone
Community Dynamics: Yellowstone National Park
to as America's Serengeti because of the large herds of wildlife
that graze on its rolling expanse."
Six species of ungulates are currently found in Yellowstone
National Park. Archaeological study has shown that bighorn sheep,
bison, pronghorn and deer (both mule and white tail) have coexisted
with elk for millennia in the Yellowstone River Valley.
Species and winter population estimates (1978) in the Northern
- Elk- 12,000
- Mule deer- 2,000
- Bighorn sheep- 500
- Bison- 260
- Moose- 200
- Pronghorn- 150
Elk are by far the most abundant ungulate in Yellowstone. Over
time, human harvest has greatly reduced mule deer, bighorn sheep
and pronghorn numbers (mid-1870-1880's). Since then, mule deer
numbers have recovered, however bighorn sheep are not as numerous
as they once were in the Yellowstone area. Houston (1982) reviewed
the dynamics of the five less abundant species were reviewed with
an emphasis on: resource division, relationships among species,
and the effects of elk upon other species.
Resource Division: To at least some extent, all
six species of ungulates are seasonally migratory. The most important
aspect of resource partitioning occurs during the winter months,
when snow levels limit food sources.
It is traditionally thought that interspecific competition,
or competition between different ungulate species, explains
resources partitioning during winter months. In Yellowstone,
it is more commonly thought that resource segregation
and food preferences (browse vs. graze) contribute
to ungulate resource division. Habitat utilization varies
seasonally by species; therefore, differences in habitat use
also play a role in the division of resources. For more detail
visit, interspecific competition
and resource segregation concepts.
Body size of the different ungulate species
also places limitations on species winter distributions. For
more information visit Allometry
concepts. This occurs for two reasons:
1) Metabolic needs: Smaller animals, such as pronghorn
and deer, need higher quality forage than larger grazers,
such as elk and bison.
2) Morphology constraint: Smaller stature animals
are not able to deal with deep snow, like larger stature animals
can. Animal chest height and foot loads are measures that
determine an animal's ability to cope with snow depth.
The effects of elk on other species: Even though
resource partitioning does occur, allowing different species to
exploit different resources, the large numbers of elk may still
impact the abundance of other ungulate species. Elk do overlap
in distribution and food habits with other species, which may
be affecting those species in a negative way. It is important
to remember that relationships between ungulate species are not
constant, and changes in climate, fire and succession may reflect
changes in interspecific partitioning and/ or competition.
Grazing Pressure: Yellowstone National Park,
and the Greater Yellowstone Ecosystem
A grazing bull elk.
Aspen: Where have they
Winter feed of elk in
human occupied winter rangeland.
How is grazing pressure created?
Elk in Yellowstone graze and browse. That is, they eat primarily
grasses and forbs. As the elk population increases in size, grazing
pressure on Yellowstone rangeland also increases. The elk population
in Yellowstone is large, and has increased in the Greater Yellowstone
Ecosystem by a factor of 2.5 from 1968-1988. In 1987-88, approximately
31,000 elk summered and 20,000 elk wintered within Yellowstone
National Park. Forage demands for elk must be met in the summer
as well as winter months. This presents a problem. Less land is
available to elk during winter months where snow covers food resources.
The consequence is increased elk density over less land area,
which increases grazing pressure on rangelands.
Is winter range limited?
Available winter range has been reduced by urban development,
agriculture, and ranching in the Greater Yellowstone Ecosystem.
Efforts have been made to reclaim historic elk winter rangeland.
Mountain Elk foundation, an independent conservation organization,
has been influential in efforts to acquire elk winter range. The
National Refuge System (USFW) acquired 25,000 acres of historic
winter rangeland for the National Elk Refuge in Jackson, Wyoming.
This is ¼ of the historic
elk winter range in the Jackson valley. Although land acquisition
efforts have achieved some level of success, many critics contend
that elk herds which summer in Yellowstone National Park are winter
range limited. Where elk have less access to winter range, grazing
pressure may reach levels higher than historically attained.
How do high levels of grazing pressure affect range condition?
High levels of grazing pressure reduce the standing crop of vegetation,
can alter plant composition and presence, increase soil compaction
and ultimately lead to habitat degradation. The concept of "overgrazing"
is defined as an excess of herbivory that leads
to degradation of plant and soil resources. The resource management
strategy one is employing will qualify what level of herbivory
is in excess. If land is being used for ranching, the management
goal would be to keep range condition at a level that sustains
maximum population yield over time. This would require less grazing
pressure. On the other hand, where land is being managed to maintain
ecological processes, grazing pressure is expected to be high
and "overgrazing" is no longer a valid concept. Where
natural regulation, or maintenance of ecological process, is the
management objective, as it is in Yellowstone National Park, the
entire ecosystem must be intact. The Greater Yellowstone Ecosystem
is not fully intact, because accessibility to and availability
of historic winter range has been altered.
Are there signs of high grazing pressure in Yellowstone?
The issue of habitat alteration caused by high grazing pressure,
or "overgrazing", is controversial. Various investigators
and authors view cause-effect relationships of habitat alteration
in Yellowstone differently.
A research exclosure in Yellowstone National Park showing
growth of aspen inside the fence where grazing is not allowed.
| One example of the controversy is the reduction
in aspen and willow trees across the Yellowstone landscape.
Chase (1987) and Kay (1990) believe that declines in aspen
and willow can be attributed to excess herbivory by elk and
that these declines may adversely affect birds, small mammals,
beavers and grizzly bears. Others, such as Houston (1982)
and Despain (1986), believe that the decline of aspen in Yellowstone
means relatively little to the ecological function of the
park. Poor fossil record of aspen and willow, at least on
the northern range, suggests that neither have ever been a
major component of vegetation in Yellowstone, and probably
did not greatly exceed present day coverage of 3% (Houston
1982). They also contend that the decline of beavers can be
attributed to a drought in the 1930's, and that beaver numbers
were artificially high previously due to the removal of predators
from the system. Exclosure studies have been conducted in
Yellowstone, which show shifts in vegetative response inside
vs. outside the exclosures. However, exclosures are not accurate
indicators of a natural system, since some level of grazing
is natural and other ungulates browse/ graze as well. Hard
evidence is missing from both sides, and the controversy over
the effects of grazing pressure on aspen and willow communities
in Yellowstone continues today.
| Another habitat alteration that has received attention
is the rate of soil erosion. Study has been conducted
on what is affecting soil erosion in Yellowstone. These investigations
were conducted to determine if elk should be blamed for soil
disturbance to Yellowstone's rangelands. According to Huff
and Varley (1999), "Yellowstone shows no significant
differences from long standing erosion patterns dating back
thousands of years." The primary sources of sediment
loading in streams come from high elevation areas that elk
do not inhabit.
Quotes from cited professionals:
"To me, the point is the ecosystem.
Is the system functioning, or are things breaking down? Are we
getting an invasion of unpalatable plants, or breaking down soils
so that their rate of nutrient recycling is going to pot? That's
what I'm looking at. And I don't see that in Yellowstone. Therefore,
as a grazing system, this is a healthy one."
1995 interview with Sam McNaughton, botany professor at Syracuse
University, taken from Yellowstone's Northern Range Newsletter.
"For many Americans the illusion
of the park as a primitive ecosystem was too attractive to be
denied. 'Natural' according to a recent report on marketing, by
the 1970's had become the most popular word in America, preferred
even to 'new' and 'improved'. Natural regulation was a triumph
Austin Chase, Playing God in Yellowstone: The Destruction of
America's First National Park, 1987.
and Elk in Yellowstone
Image by Monty Sloan, Wolf Park,
A Brief History –
By the 1930’s, wolves were completely eliminated from Yellowstone.
Without wolves, elk in the park had no natural predators. In
1935, park managers began a culling program to reduce elk herds,
thus replacing predator-induced mortality with man-induced mortality.
In 1968, when the culling program was halted, the Northern elk
herd population was at about 5000. At this time, elk herds quickly
began to grow. By 1988, the Northern elk herd had reached a population
Their place in the ecosystem –
Wolves play an important role in the ecosystem of Yellowstone.
As the top carnivore, they act as a natural regulator for prey
species, including elk. It is believed by many ecologists that
elk herds (as well as other ungulates in the park) experienced
a population explosion in the absence of the wolf. However, when
the wolf was restored to the park in 1995, it was not the belief
of biologists that elk numbers would suddenly be controlled.
Elk can benefit from the presence of wolves in the park. While
wolves usually prey upon females or younger elk, it is not uncommon
for them to kill the weakest members of the elk herds. The weaker
elk generally can’t escape as fast as the healthier elk. By removal
of the “less fit,” or weaker, elk and persistence of the “more
fit,” or stronger elk, natural selection for a strong herd takes
So will the wolves impact elk populations?
Between the years of 1995 and 1997, a total of 41 wolves were
released in the park. Each wolf pack takes one elk every one
to five days. 85% of a wolf's diet consists of elk. In the year
1997, there were 86 wolves in the Greater Yellowstone area. In
that same year, 234 elk kills were detected by wolf project staff,
who monitor predation on ungulates. Today, there are about 115-120
wolves present in the Greater Yellowstone area. Compared to the
over 120,000 elk that reside in the Greater Yellowstone area today,
it may be several years before wolves have an impact on elk populations.
It is believed by experts that ten years after reintroduction,
100 wolves would reduce the elk population by less then 20%. However,
according to Kerry Murphy, a wolf biologist from Yellowstone,
there has been an 8-20% decrease in elk populations due to wolf
predation within the last five years.
It is unknown if the current elk population trends are due to
wolves or some other environmental factor. The wolves were released
in 1995 and there were no elk counts made for two years. A 1999
elk count showed a drop in elk population, but it's too soon to
attribute that to wolves.
For more information on wolves in Yellowstone, click
Influence of Human Disturbance on Elk of the Yellowstone National
main roads system found in Yellowstone.
Roads can affect the elk within the Yellowstone
National Park area. There are five park entrances, 466 miles
of roads and 1000 miles of backcountry trails, which all effect
elk in their migratory patterns and foraging ability. The
total number of vehicles on the roads in July of 1999 was
398,680, and in January 2000 were 62,815. The number of vehicles
deters the elk from coming in contact with certain areas of
the park. Roads increase sedimentation in streams and waterways
leading to a decline in water quality. Motorists can kill
elk crossing roads. Elk also have smaller habitats to occupy
because of motorists disturbance. When elk use the roads
during winter months for easier traveling, they run the risk
of getting hit by cars. Elk crossing the highways often lose
group members; thus spending extra energy trying to locate
lost members during migration. The above is a diagram of the
main roads located in Yellowstone National Park.
mortality on the edge of human settlement.
Human settlement has an impact on the
elk population, densities and migratory patterns. 3000 to
4000 elk spend the summer in the southern areas of the park
then migrate to northern Yellowstone National Park for better
feeding grounds. Migration North occurs to increase the quality
of forage and decrease the energy spent on finding food. Humans
have taken up residence in the winter range of the elk for
agriculture or developments. Human settlement has lowered
the quality of forage and increased competition with livestock.
In response, elk have changed migration routes to avoid humans.
example of an ungulate- snowmobile interaction.
Winter activities have flourished in
the Yellowstone National Park area. One form of winter recreation
in particular is snowmobiling. With snowmobiles, people are
able to go places not possible before. When snowmobile activity
increased, elk population counts lowered in those areas, decreasing
habitat availability. Compacted snowmobile trails offer a
slight benefit to elk by lowering energy use during migration
foraging along a riverside.
Water quality has become a major issue
within the park because of human disturbance. Road building
increases the level of sediment input to stream and river
systems. Human settlement leads to a reduction in available
clean water and increases in waste. Agriculture and industrial
water uses have also increased. Hydro-development and pollution
from mining, herbicide, and pesticide use from timber and
crop production negatively affect water quality. All of
these circumstances impact habitat that elk use.
The Bureau of Land Management and the National Park
Service have an opportunity to utilize the resources available
on Yellowstone. One resource that has been utilized is the timber.
As far as the economics of the timber industry within Yellowstone,
the Bureau of Land Management states that for the year of 1999
timber, wood products and non-timber product sales were $52,891.95.
Yellowstone National Park has turned logging that once was a seasonal
occupation into a year-round activity. This change has also affected
the elk within these areas.