America’s “Serengeti” at risk: Population-driven sprawl threatens the Greater Yellowstone Ecosystem

From the Everglades to the Arctic plains, population growth and associated development threaten America’s protected areas. A recent study from NumbersUSA, Greater Yellowstone: An Ecosystem at Risk, documents this for the United States’ flagship national park.

By Leon Kolankiewicz and Rob Harding

Rampant development and a surging human population are imperiling what has been dubbed “America’s Serengeti”: the iconic Greater Yellowstone Ecosystem.

Established in 1872, Yellowstone National Park was the very first in the world. While originally set aside for its unrivaled geologic and hydrothermal features (e.g., geysers and hot springs), Yellowstone has also played a critical role in the survival of such iconic wildlife as the American buffalo or bison (Bison bison), gray wolf (Canis lupus), and grizzly (brown) bear (Ursus arctos).

Yellowstone preserves some 2.2 million acres (about 890,000 hectares or 8,900 square kilometers) of wildlands and wilderness reaching into three states in the northern Rocky Mountains: Wyoming, Montana, and Idaho. Urban developments such as housing subdivisions, office districts, and shopping malls are all prohibited in this publicly-owned and protected national park. These habitat-destroying incursions are also banned in neighboring Grand Teton National Park, five national forests, three national wildlife refuges, and the Wind River Indian Reservation, collectively known as the Greater Yellowstone Ecosystem (GYE) or just Greater Yellowstone.

However, privately-owned lands make up about one quarter of Greater Yellowstone’s 23 million acres (93,000 square kilometers, larger than Scotland!). Most of these private lands are still rural – in a mix of cropland, pastureland, rangeland, and forest – that is, mostly cultivated farmland and ranchland used for crop and forage production and livestock (mostly cattle) grazing.

While privately-owned and often altered or degraded by agricultural practices, these typically lower-elevation lands are still ecologically crucial for the migration and over-wintering of large ungulates (herbivorous hooved mammals) such as elk or wapiti (Cervus canadensis), mule deer (Odocoileus hemionus), pronghorn (Antilocapra americana), moose (Alces alces), and bison. Even with a warming climate, the rugged mountain ranges and high elevations in the Northern Rockies still experience deep snow and harsh conditions, which many mammals have avoided since time immemorial by migrating to lower lands and habitats for the winter months.

Unfortunately, these ancient seasonal pilgrimages and survival strategies in the GYE are now threatened by a booming human population, the development and sprawl it engenders, and the attendant loss and fragmentation of crucial winter habitat. 

Increasing human numbers in Greater Yellowstone not only leads to permanent wildlife habitat loss, degradation, and fragmentation, but increased mortality of wildlife from collisions with vehicles on ever busier roads. This past October, arguably the most famous grizzly bear in the world, Grand Teton National Park’s Grizzly 399, a 28-year old female that was still reproductively active and known to have raised 18 cubs over her lifetime, “was fatally struck by a vehicle on Highway 26/89 in Snake River Canyon, south of Jackson, WY outside of Grand Teton National Park,” according to the National Park Service.

Already the third-most populous country on Earth in 1990 at 250 million, America’s numbers grew by 32 million in the 1990s, 27 million in the 2000s, and 22 million in the 2010s. At the peak of de facto “open borders” immigration folly under the recent Biden Administration, immigration alone added another 3.5 million in a single year (2023). If extended for a decade, and added to net natural increase (births minus deaths), this would easily exceed 40 million. Today the United States is pushing a bloated 340 million human residents and the population continues to grow with no end in sight. 

While the new Trump-Vance administration promises to slash illegal immigration, they seem supportive of increasing legal immigration, and the new vice-president has heaped scorn on “childless cat ladies.” It appears that the new administration endorses the mantra “growth is good and more is better.”

This rapid national growth has paralleled and helped propel a population boom in the Northern Rockies, as more Americans flee overpopulated, overcrowded, increasingly dysfunctional states like California for the “greener pastures” of regions that until recently, enjoyed quite low population density or what Americans call ample “elbow room”.

NumbersUSA recently completed a study, called Greater Yellowstone: An Ecosystem at Risk, which quantifies the relative importance of the two main factors driving urban sprawl and the permanent conversion of rural land to developed land in the Greater Yellowstone Ecosystem. All of this rural land is wildlife habitat, agricultural land, or both.

These two main drivers of sprawl are: 1) population growth, that is, an increase in the number of residents (consumers of developed land); and 2) increase in the average consumption or use of developed land per capita, i.e., per person.  

We used a mathematical formula originally used to assess the relative weights of increasing population size and per capita energy use in determining America’s aggregate energy consumption. This approach can be extended to any natural resource, the aggregate consumption of which is increasing over time, due to a changing number of resource consumers, changing per capita resource consumption, or both. In our study, rural, undeveloped land is the natural resource in question.

We used data from two federal government agencies: the Natural Resources Conservation Service (NRCS) of the U.S. Department of Agriculture and the U.S. Census Bureau (USCB). NRCS National Resources Inventories (NRIs) have estimated land use and cover on America’s non-federal lands in all 3,144 counties in the U.S. every five years since 1982. USCB estimates county populations annually. With both datasets available from 1982 to 2017 (the most recent year for the NRI), we derived estimates of the percentage of sprawl in Greater Yellowstone related to population growth and to increasing per capita developed land consumption. That is to say, if the area of sprawl increased to the same extent as population growth, with the same area of developed land per person, then the sprawl would be due solely to population growth. However, if the area of developed land per person also increases then part of the impact is due to per capita land consumption.

The area of developed non-federal land in the 20 GYE counties grew from 345,300 acres (140,000 hectares or 540 square miles) in 1982 to 497,400 acres (201,300 hectares or 777 square miles) in 2017, an increase of 44% or 152,100 acres (61,550 hectares or 237 square miles). Approximately 67% of this increase was related to population growth and 33% to increasing per capita developed land consumption. In the most recent 2002-2017 subset, 85% of the sprawl was related to population growth. These results may underestimate the adverse effects of low-density exurban sprawl on habitat fragmentation and large mammal migration. 

By 2060, the aggregate population of the GYE counties is projected to grow from approximately 540,000 in 2022 to about 765,000, an increase of about 225,000 or 42%. If average population density were to stay the same, this would lead to the loss of another 232,000 acres (94,000 hectares, or 362 square miles) of rural land (e.g., habitat, ranchland). This loss would likely entail significant adverse, long-term effects on biological diversity and abundance, in particular Greater Yellowstone’s large mammals.

As we said to the 16^th Biennial Scientific Conference on the Greater Yellowstone Ecosystem in September 2024:

Avoiding this undesirable outcome will require a combination of: 1) effective local planning measures and, 2) commitment to national population stabilization. Each is necessary, neither is sufficient in itself, to preserve the unique character and iconic wildlife of the GYE.

The good news is that there is political support both among Americans generally and Greater Yellowstone residents in particular for actions to control sprawl at both the local and national levels. This was clearly revealed in the results of polling conducted last summer by Rasmussen Reports and NumbersUSA. Majorities supported both local measures such as zoning and urban growth boundaries, and national measures such as reducing the level of annual immigration admissions to slow national population growth that is the indirect or underlying driver of growth in the GYE and development pressures wildlife face. 

Both local and national measures face stiff political headwinds among elected officials, but so have many ultimately successful conservation efforts over the years. As author and veteran journalist Todd Wilkinson, founder of the conservation journalism website Yellowstonian (yellowstonian.org), wrote in the closing words to the foreword of our study:

…there is only one Yellowstone and one Greater Yellowstone Ecosystem. If we can’t succeed in protecting this bioregion, then what hope, really, do we have for saving anyplace else?

Leon Kolankiewicz is an environmental consultant, conservation biologist, vice president of Scientists and Environmentalists for Population Stabilization, and scientific director at NumbersUSA.

Rob Harding is Sustainability Outreach Liaison at NumbersUSA, board member of The Rewilding Institute, trustee of WILD Foundation, and chapter director of Center for the Advancement of the Steady State Economy.