Yellowstone National Park

Gateway communities at the park’s entrances provide many services that need not be duplicated in the park, thus reducing the visitor development needs in the park and lessening the impact of those needs on the park’s values. However, the type and scale of development at the gateway communities may impact the natural beauty of the park as well as animal movements between the park and the surrounding Greater Yellowstone Ecosystem (GYE).
In recent decades, population growth, development, and sprawl on private lands within the 20 counties that comprise the GYE have permanently converted hundreds of square miles of open space – all of it agricultural land, wildlife habitat, or both – into developed or urbanized land. Resulting habitat loss and obstruction of traditional wildlife migration corridors have adversely impacted the ecological integrity of the GYE and its extant populations of large ungulates and carnivores. The area of developed non-federal land in the 20 GYE counties grew from 345,300 acres 9539.5 square miles) in 1982 to 497,400 acres (777.2 square miles) in 2017, an increase of 44% or 152,100 acres (237.7 square miles). Approximately 67% (161 square miles) of this increase was related to population growth and 33% (79 square miles) to increasing per capita developed land consumption. In the most recent 2002-2017 subset, an even higher portion of the sprawl, 85%, and rural land lost to development were related to population growth. These results may underestimate the adverse effects of low-density exurban sprawl on habitat fragmentation and large mammal migration. This driver has grown especially pronounced since the Covid-19 pandemic, as wealthy out-of-staters have moved into the GYE from places like California, building large homes and ranchettes on often fenced large lots, which themselves can pose barriers to large mammal movement; this trend shows no sign of letting up. Under current demographic trends in the region, by 2060, the aggregate population of the GYE counties is projected to grow to 763,471, from 538,702 in 2022, an increase of 224,769 or 42%. If average population density were to remain constant, this growth would lead to the conversion of approximately another 231,500 acres (362 square miles) of non-federal rural land (e.g., natural habitat, ranchland) to developed properties. These newly developed areas would be unevenly distributed at varying densities throughout the GYE. In sum, their aggregate area and configuration – and the concomitant habitat loss and fragmentation – would entail potentially significant adverse, long-term direct, indirect, and cumulative effects on wildlife, especially large mammals with large home ranges and/or long seasonal migration routes (Kolankiewicz et al. 2024).

Fish from outside the park, including non-natives such as eastern brook trout (Salvelinus fontinalis) and lake trout (Salvelinus namaycush), which compete with native species, were introduced as early as 1890. Lake trout were discovered in Yellowstone Lake in 1994 and they increased greatly, while native cutthroat trout declined. Lake trout control measures began in 1995 and although numbers have been reduced, eradication is virtually impossible. Other non-native aquatic species include lake chub (Couesius plumbeus), brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss), Myxobolus cerebralis, a parasite that causes whirling disease in cutthroat trout and other species, New Zealand mud snails (Potamopyrgus antipodarum) and Red-rimmed melania (Melanoides tuberculatus) (National Park Service, 2020c). In 2016 the Greater Yellowstone Coordinating Committee published an Aquatic Invasive Species Cooperative Strategic Plan that calls for a) preventing new introductions and limiting the spread of existing populations; b) abating ecological, socioeconomic, and public health and safety impacts resulting from infestations of aquatic invasive species; and c) providing a cooperative environment that promotes coordination among all Greater Yellowstone Area stakeholders (Greater Yellowstone Coordinating Committee, 2016). There are 225 documented non-native species of plants in Yellowstone. They include Canada Thistle (Cirsium arvense), Dalmatian Toadflax (Linaria dalmatica), Houndstongue (Cynoglossum officinale), Leafy Spurge (Euphorbia esula), Ox-eye Daisy (Leucanthemum vulgare) and Spotted Knapweed (Centaurea maculosa) (National Park Service, 2020d). Non-native bird species include Eurasian collared dove (Streptopelia decaocto), starling (Sturnus vulgaris) and house sparrow (Passer domesticus) (National Park Service, 2014). Few non-native mammals are established in the park other than mountain goats (Oreamnos americanus). The impacts from these invasive and introduced species are felt throughout the park and result in loss of native habitats and species.

Annual Yellowstone National Park visitation has increased close to 59% since the early 2000s. Yellowstone visitation rose to historic levels of 4.8 million and 4.5 million visits in 2021 and 2023, respectively (National Park Service, 2025a). Staffing levels have remained relatively consistent since 2000. The increase in visitation poses several challenges with overcrowding, vandalism, loss of natural light and sound quality and reduction in wildlife viewing opportunity having been reported (Jorgenson, et al., 2019, National Park Service, 2014a). This increase in visitation has also brought safety issues including traffic volumes in high-use corridors approximately 30% higher than roads and parking lots can safely handle. Additionally, since 2008 a 90% rise in motor vehicle accidents, 60% more ambulance use, and 130% more search and rescue efforts. Vehicular demand was projected to exceed capacity between 2021 and 2023 (Otak, Fehr and Peers, 2017, 2018, Jorgenson, et. al., 2019). However, a 2018 Visitor Use Study indicates that visitor experience levels remain high, and monitoring efforts show no population level impacts or resource impairment at current visitation levels (IUCN Consultation, 2020). Moreover, impacts from increasing visitation, whether on resources, staff/operations, or experience, are reportedly localized and site-specific (IUCN Consultation, 2020).

In 2019, Yellowstone developed a strategy to better understand and respond to impacts from increasing visitation. The strategy focuses on visitor impacts to these four areas: Park Resources; Park Staffing, Operations, and Infrastructure; Visitor Experience; and Gateway Communities (Yellowstone National Park, 2023).

While the park continues to implement management actions to address increased visitation through a focus on improving operations and provide a better visitor experience in key congested areas, Yellowstone has not begun a formal planning process for visitor use management. If visitation continues to rise, future management strategies could include (but aren’t limited to): operational and staffing changes; communication and traffic management systems; shuttle systems or other transportation alternatives; and reservations or timed-entry systems at specific sites where demand exceeds capacity (Yellowstone National Park 2025b).

The site management are working to evaluate and respond to increasing visitation in the following key areas: 1) impacts on resource conditions; 2) impacts on staffing, operations, and infrastructure; 3) impacts on visitor service levels; and 4) impacts on gateway communities and partners. The park has and will continue to use a range of data to develop actions that improve performance in the four key areas. Recent and upcoming park actions include major projects at the Grand Canyon of the Yellowstone, a new North Entrance station, pilot projects to alter traffic and parking, mapping efforts and on-the-ground surveys to analyse social trails and resource impacts, evaluation of shuttle systems, improvements at Norris Geyser Basin, road improvement projects, and a West Yellowstone Gateway study (IUCN Consultation, 2020).

Restriction of grizzly bear range was identified by the World Heritage Committee (WHC) in 2010 as a threat to be addressed (Berger, 2004). While early studies expressed that isolation of the Yellowstone population over the past 100 years has led to a reduction in genetic variability and reduced the demographic viability of the population (Craighead and Vyse, 1996, Knibb, 2008; World Heritage Committee, 1978), more recent genetic data indicates that the population has grown since the 1980s with no loss in genetic diversity. Meanwhile, the effective population size has increased 4 –fold over a 25 year period (Kamath et., al. 2015).

To date, no radio-collared grizzly bears are known to have successfully travelled to the Selway-Bitterroot or the Northern Continental Divide Grizzly Bear Recovery Zones from Yellowstone, but they have expanded their range in recent years into closer, smaller areas of secure habitat.

To enhance the genetic viability of grizzlies in the Greater Yellowstone Ecosystem, and to better provide the conditions for the delisting of the grizzly bear from the Endangered Species list, Montana's Fish Wildlife and Parks translocated 2 grizzlies from the Northern Continental Divide Ecosystem to the Greater Yellowstone Ecosystem. The translocations included one subadult female moved south of Yellowstone National Park, and one subadult male moved inside Yellowstone National Park to the shore of Yellowstone Lake (Montana Fish Wildlife and Parks, 2024).

On January 8, 2025, the U.S. Fish and Wildlife Service rejected petitions from the states of Montana and Idaho to delist the grizzly bear from the list of endangered species under the federal Endangered Species Act (U.S. Fish and Wildlife Service, 2025). This current rule is now under review by the current administration, after a recent election.

Bison (Bison bison) are an iconic feature of Yellowstone and the national mammal of the USA However, the threat of brucellosis transmission to cattle and the real and perceived conflicts, such as competition for grasses, public safety and property damage, has limited the tolerance for bison that range outside the park. To address these issues and the management of bison generally inside the park, an Interagency Bison Management Plan (IBMP) was developed in 2000 by officials from the park and the State of Montana. A new bison planning process commenced in 2022 and was finalized in July 2024. The new Yellowstone National Park Bison Management Plan includes the following provisions: the National Park Service (NPS) will work with partners to control bison population numbers using Bison Conservation Transfer Program (BCTP) to restore bison to Tribal lands, Tribal Food Transfer Program (TFTP) to provide meat and hides to Tribes, Tribal and state harvests outside the park. The NPS will prioritize the BCTP and place bison in the BCTP when bison migrate to the park boundary and there is space in the facility. The NPS will establish a population assurance threshold of 5,200 bison. When the population reaches the 5,200 threshold, the NPS will begin to reduce the bison population by relying primarily on Tribal and state harvests. If harvests do not reduce numbers, the NPS will remove additional bison through the TFTP. When the population is below 5,200, the NPS will only place bison in the BCTP and use the TFTP to remove brucellosis-positive bison that are identified when animals are selected for the BCTP. If the late-winter population nears 3,000 animals, the NPS will protect the population inside the park and encourage partners to reduce hunting outside the park.

In 2024, 68 bison were removed: 5 placed in the BCTP, 14 donated to the TFTP, 48 harvested (15 by state hunters and 33 by tribal members), and 1 mortality in the NPS bison management facility (Interagency Bison Management Program, 2024).

In January 2025, the state of Montana filed a lawsuit in federal court against Yellowstone National Park arguing that park officials failed to provide adequate consultation and the park ignored their own science in an effort to increase Yellowstone National Park bison numbers and avoid vaccinating them against brucellosis (State of Montana, 2025).

Whitebark pine plays an important role in retaining snow, reducing erosion, acts as a nurse plant for other subalpine species and produces seeds that are an important food for birds, grizzly bears and other wildlife. A 2013 aerial survey showed approximately 46% mortality of whitebark pine inside the Park. White pine blister rust, caused by the nonnative fungus, Cronartium ribicola, slowly damages and can eventually kill infected whitebark pine trees. Periodic outbreaks of native mountain pine beetle (Dendroctonus ponderosae), quickly decimate infested whitebark pine forests. Beetles preferentially attack larger, mature whitebark pine. The historical suppression of wildland fire has resulted in more frequent, bigger, and hotter wildfires. Finally, climate change exacerbates each of these stressors. Specifically, warmer temperatures enable mountain pine beetle to reproduce in one-year rather than multi-year cycles. Between 2007 and 2009, this shift resulted in a mountain pine beetle epidemic that killed 80% of the oldest trees in the ecosystem (National Park Service, 2020f, 2020g).

The gray wolf (Canis lupus), eliminated from the park by the 1920s under a different park management philosophy, was successfully reintroduced into the Park in 1995 (State Party of the USA, 2015; Povilitis, 2015). Similarly, the grizzly bear (Ursus arctos horribilis), generally eradicated from the western United States except in Yellowstone, found refuge in the park. The grey wolf (Canis lupus) is an iconic species that represents Yellowstone. As wildlife generally has little understanding of park boundaries, hunting outside the park can have a significant effect on those animals that generally inhabit the park. For example, 13 wolves known to live in Yellowstone National Park, that represented 10% of the winter 2023-2024 Yellowstone wolf population, were hunted outside the park in Montana during the 2023-2024 hunting season (Outdoor Life, 2024).

Hunting can risk reducing overall wolf population size (Creel and Rotella 2010), longevity of family lineages, and intergenerational transfer of adaptive genetic and cultural information (Haber 1996; Haber and Holleman 2013).

Yellowstone has partnered with neighbouring states and associated foundations to increase the knowledge of these species and conduct public outreach and lessen the impact of hunting outside the Park. These partnerships include the Interagency Grizzly Bear Committee, Wyoming Bear Wise Project and the Yellowstone Ecosystem Committee (State Party of the USA, 2015).

In 2017, grizzly bears were removed from the U.S.A. Endangered Species List by the U.S. Fish and Wildlife Service, though the Endangered status was reinstated by court action in 2018. The court ruled that the government did not adequately consider the role of connectivity of isolated grizzly subpopulations in ensuring genetic variability (Washington Post, 2018). Currently, wolves are not listed under the Federal Endangered Species List in Montana, Wyoming and Idaho, the three states bordering Yellowstone National Park. Wolves are hunted in the three states under state hunting regulations (Yellowstone National Park, 2025a).

Future climate models for the Greater Yellowstone Area (GYA) all predict increasing temperatures, but differ in whether to expect more, the same, or less precipitation (National Park Service 2020j). Increased evapotranspiration driven by warmer temperatures is projected to be large enough, however, to result in overall drier conditions, regardless of the precipitation scenario. Conditions in Yellowstone, therefore, are projected to become hotter and drier, especially during the summer and fall. In Mammoth Hot Springs, the five-year running mean of average annual daily maximum temperature has increased by 1.2° Celsius (2.1°F) and the average annual daily minimum temperature has increased by 2.2° Celsius (3.9°F) during 1941–2016 (Yellowstone Center for Resources, 2018, National Park Service, 2020g). By the middle of the 21st century (2030-2059), average temperatures in the Greater Yellowstone Area in the spring are expected to warm by 1.6 to 2.4°C (2.9° to 4.3°F), in the summer by 2.6 to 3.0°C (4.7° to 5.4°F), in the fall by 2.3 to 2.7°C (4.3° to 4.9°F) and 1.7 to 2.3°C (3.1° to 4.1°F) in the winter (National Park Service, 2020i). There is an overall continued decline in snowfall projected for Yellowstone over the coming decades most pronounced in spring and summer (National Park Service, 2020j).

Total annual precipitation at Mammoth Hot Springs since 1976 has been generally below the long-term mean of 38.9 cm (15.3 inches). The five-year running mean of annual peak snowpack at the Northeast Entrance has declined 30% since 1966, from 38.2 cm to 26.5 cm (15.02 inches to 10.44 inches). Analyses of streams during 1950–2010 in the Central Rocky Mountains, including those in the Greater Yellowstone Ecosystem, show an 89% decline in stream discharge (National Park Service, 2020j).

Snowy conditions have been prevailing for a shorter period during the year. The 10-year running mean of winter length at the Northeast Entrance SNOTEL station has decreased 15% during 1966–2017, from 216 to 183 days. Even if precipitation recovers to historical levels, which models indicate is possible, increased temperatures and evapotranspiration will reduce water availability (National Park Service, 2018, 2020g).
Potential impacts of decreased snowpack and less precipitation leading to extended periods of drought in the region in the future may result in geyser eruption intervals lengthening and perhaps even cessation of geysering due to the inability of geysers to replenish themselves (Hurwitz, et al., 2008).

Impacts from these climate change-induced conditions include a) an increase in size, intensity and frequency of fires due to climate change; b) declining air quality in summer months due to increased forest fires; c) increases in temperature and water temperature may increase suitability for the spread of aquatic invasive species and invasive plants (Yellowstone Center for Resources, 2018); d) increased frequency of and intensity of insect outbreaks including bark beetle infestations have resulted in a 79% mortality rate of mature whitebark pine trees (National Park Service, 2020j); e) longer growing seasons and changes in seasonal growth patterns will likely disrupt vegetation growth and development, causing plants to bud, flower, fruit and die at different times of the year than they do now. Those changes, in turn, would alter or seriously disrupt wildlife migrations, in particular, elk (Cervus canadensis) that move through the park (Rickbeil, et al. 2019), one of the key resources for which Yellowstone National Park is globally treasured (National Park Service, 2020j).