Yellowstone Handbook 2019
Greater Yellowstone Ecosystem
Yellowstone Resources and Issues Handbook. Published by the National Park Service (NPS).
Greater Yellowstone Ecosystem At 3,437.5 square miles (8,903 km2),Yellowstone National Park forms the core of the Greater Yellowstone Ecosystem—one of the largest nearly intact temperate-zone ecosystems on Earth. Greater Yellowstone’s diversity of natural wealth includes the hydrothermal features, wildlife, vegetation, lakes, and geologic wonders like the Grand Canyon of the Yellowstone River. Heart of an Ecosystem Yellowstone National Park was established in 1872 primarily to protect geothermal areas that contain about half the world’s active geysers. At that time, the natural state of the park was largely taken for granted. As development throughout the West increased, the 2.2 million acres (8,903 km2) of habitat that now compose Yellowstone National Park became an important sanctuary for the largest concentration of wildlife in the lower 48 states. The abundance and distribution of these animal species depend on their interactions with each other and on the quality of their habitats, which in turn is the result of thousands of years of volcanic activity, forest fires, changes in climate, and more recent natural and human influences. Most of the park is above 7,500 feet (2,286 m) in elevation and underlain by volcanic bedrock. The terrain is covered with snow for much of the year and supports forests Quick Facts Space and Ownership • 12–22 million acres; 18,750– 34,375 square miles (Sizes, boundaries, and descriptions of any ecosystem can vary.) • States: Wyoming, Montana, Idaho • Encompasses state lands, two national parks, portions of five national forests, three national wildlife refuges, Bureau of Land Management holdings, private and tribal lands. • Managed by state governments, federal government, tribal governments, and private individuals Wildlife • One of the largest elk herds in North America Management Challenges • Climate change • Invasive species • Managing an ecosystem across political boundaries • Land use change • In Yellowstone: • Largest free-roaming, wild herd of bison in United States • One of few grizzly populations in contiguous United States −− Grizzly bear management • Rare sightings of wolverine and lynx −− High visitation −− Bison management −− Native fish conservation Greater Yellowstone Ecosystem 53 E CO S YS T E M The Greater Yellowstone Ecosystem, with Yellowstone at its core, is one of the largest nearly intact temperatezone ecosystems on Earth. the Yellowstone Plateau itself is a result of uplift due to hot-spot volcanism. Today’s landforms even influence the weather, channeling westerly storm systems onto the plateau where they drop large amounts of snow. The volcanic rhyolites and tuffs of the Yellowstone Influence of Geology Caldera are rich in quartz and potassium feldspar, Geological characteristics form the foundation of which form nutrient-poor soils. Thus, areas of the an ecosystem. In Yellowstone, the interplay between park underlain by rhyolites and tuffs generally are volcanic, hydrothermal and glacial processes, and characterized by extensive stands of lodgepole pine, the distribution of flora and fauna, are intricate. The which are drought-tolerant and have shallow roots topography of the land from southern Idaho norththat take advantage of the nutrients in the soil. east to Yellowstone probably results from millions of In contrast, andesitic volcanic rocks that underlie years of hot-spot influence. Some scientists believe the Absaroka Mountains Billings ! are rich in calcium, magLivingston ! Bozeman ! nesium, and iron. These minerals weather into M O N T A N A soils that can store more water and provide better Custer Gallatin Red Lodge nutrients than rhyolitic National Forest ! National Forest soils. These soils support Gardiner Cooke City ! ! more vegetation, which Beaverhead-Deerlodge adds organic matter and Yellowstone National Forest National Park enriches the soil. You can Red Rock Lakes see the result when you ! West Yellowstone National Wildlife Refuge drive over Dunraven Pass ! Cody Shoshone National Forest or through other areas of the park with Absaroka Caribou-Targhee National Forest rocks. They have a more diverse flora, including John D. Rockefeller, Jr. Memorial Parkway mixed forests interCamas National spersed with meadows. Wildlife Refuge Grand Teton Rexburg ! National Park Lake sediments deposited W Y O M I N G during glacial periods, National Elk such as those underlying Refuge ! ! Idaho Falls Jackson Hayden Valley, form clay Bridger-Teton soils that allow meadow National Forest I D AH O communities to outcompete trees for water. Grays Lake National Wildlife Refuge The patches of lodgepole pines in Hayden Valley Pocatello ! grow in areas of rhyolite rock outcrops. Because of the influBureau of Land Management Continental Divide ence rock types, sediFish and Wildlife Service Rivers and Lakes ments, and topography Forest Service 0 50 Kilometers State Boundary North National Park Service have on plant distribuState Land 0 50 Miles tion, some scientists theorize that geology The Greater Yellowstone Ecosystem. Description of an ecosystem’s size, boundaries, also influences wildlife and characteristics can vary greatly. E C O S YS T E M dominated by lodgepole pine and interspersed with alpine meadows. Sagebrush steppe and grasslands on the park’s lower-elevation ranges provide essential winter forage for elk, bison, and bighorn sheep. l 54 Yellowstone Resources and Issues Handbook, 2019 distribution and movement. Whitebark pine nuts are an important food source for grizzly bears during autumn. The bears migrate to whitebark pine areas such as the andesitic volcanic terrain of Mount Washburn. Grazing animals such as elk and bison favor the park’s grasslands, which grow best in soils formed by sediments in valleys such as Hayden and Lamar. The many hydrothermal areas of the park, where grasses and other food remain uncovered by snow, provide sustenance for animals during winter. The Clean Air Act Amendments of 1977 designated Yellowstone and Grand Teton among the 156 national parks and wilderness areas that are Class I airsheds, requiring the most stringent air-quality protection within and around their boundaries. Yellowstone and Grand Teton are in compliance with federal air quality standards for human health. However, airquality trends may be affecting other aspects of the ecosystem. Even at relatively low levels, such as those found in the Greater Yellowstone Ecosystem, air pollution and the subsequent deposition of pollutants in water and soil can leach nutrients from the Earth, injure vegetation, and acidify and over-fertilize lakes and streams. The thin soils, sparse vegetation, short growing seasons, and snow-based water supply of these high elevation areas limit the amount of nitrogen that plants can effectively use. These conditions make the area more vulnerable to the effects of acidification and nutrient enrichment from nitrogen deposition. For example, nitrogen in precipitation has increased at many western sites as a result of fertilizer use and feedlots. Although nitrogen is a nutrient needed for plant growth, too much nitrogen disrupts native plant communities that are adapted to low-nitrogen conditions; high nitrogen levels can advance the spread of nonnative species that increase fire frequency. Acidification of high-alpine lakes from sulfur and nitrogen deposition can cause the loss of macroinvertebrates and fish. Long-term changes in the composition of algae in several alpine lakes in Yellowstone and Grand Teton are correlated with increased nitrogen. Naturally occurring ozone in the upper atmosphere protects life by absorbing the sun’s ultraviolet rays, while ground-level ozone is a pollutant that forms when nitrogen oxides from vehicles, power plants, and other sources combine with volatile organic compounds. Ozone concentrations Sources of Particulate Matter The largest source of particulate matter in Greater Yellowstone is smoke from wildland fires, which is considered part of the area’s “natural background conditions” and is taken into consideration in establishing the threshold for “good” visibility. Emissions from prescribed fires have been relatively insignificant. Because of prevailing winds, Wyoming oil and gas development has not had a detectable effect on air quality in Yellowstone. Soundscapes The Greater Yellowstone Ecosystem has many biological sounds with important ecological functions for reproduction and survival. Birds, mammals, amphibians, and insects often need to hear or produce sounds to attract mates, detect predators, find prey, and/or defend territories. The occurrence of sounds in a particular area forms the soundscape. The natural soundscape of the Greater Yellowstone Ecosystem delights visitors during the fall elk rut, during birds’ spring choruses, along rushing streams, and in the still and profoundly quiet days and nights of winter. Natural soundscapes are a resource and are protected by National Park Service policies. Many park visitors come to national parks to enjoy serenity and solitude and expect to hear sounds of nature. Sounds associated with human activity, including road traffic, aircraft, and snowmobiles, often impact these natural soundscapes and are a source of growing concern. Aircraft noise, which is the most widespread human-caused sound in the park, is heard on average for less than 10 percent of the day. Yellowstone and Grand Teton national parks initiated a soundscape monitoring program in 2003. More Information Ambrose, S, and S. Burson. 2004. Soundscape studies in National Parks. George Wright Forum 21:1 29–38. National Park Service Air Resources Division: www.nature. nps.gov/air. Greater Yellowstone Ecosystem 55 E CO S YS T E M Air Quality in Yellowstone typically peak in spring rather than summer, indicating that human influences are less significant than changes in atmospheric circulation and lengthening daylight. Nonetheless, in addition to potentially causing respiratory problems in people, ozone levels during the growing season may be high enough to prevent sensitive species, such as aspen, from reaching full growth potential. E C O S YS T E M Yellowstone waters provide essential moisture to much of the American West and water resources provide recreational opportunities, plant and wildlife habitat, and scenic vistas. Water The water that flows through Yellowstone National Park and the Greater Yellowstone Ecosystem (GYE) is a vital national resource. The headwaters of seven great rivers are located in the GYE, and flow from the Continental Divide through communities across the nation on their way to the Pacific Ocean, the Gulf of California, and the Gulf of Mexico. Precipitation (rain and snow) in the mountains and plateaus of the Northern Rockies flows through stream and river networks to provide essential moisture to much of the American West; and water resources provide recreational opportunities, plant and wildlife habitat, and scenic vistas. Water also drives the complex geothermal activity in the region and fuels the largest collection of geysers on Earth. Precipitation and groundwater seep down into geothermal “plumbing” over days, and millennia, to be superheated by the Yellowstone Volcano and rise to the surface in the form of hot springs, geysers, mudpots, and fumaroles. Yellowstone contains some of the most significant, Waters of Yellowstone near-pristine aquatic ecosystems found in the United States. More than 600 lakes and ponds comprise approximately 107,000 surface acres in Yellowstone—94 percent of which can be attributed to Yellowstone, Lewis, Shoshone, and Heart lakes. Some 1,000 rivers and streams make up approximately 2,500 miles of running water. Thousands of small wetlands—habitats that are intermittently wet and dry—make up a small (approximately 3%) fraction of the Yellowstone landscape. Lakes Yellowstone’s inland lakes are essential aquatic habitat for resident species. They are largely protected from many of the environmental stresses to which waters outside the park boundaries may be victim. These lakes maintain freshwater biodiversity, support elaborate food webs, and underpin plant and animal communities. Understanding the complexities of Yellowstone’s lake ecosystems allows park managers to successfully conserve Yellowstone’s lake resources in the face of nonnative invasive species, climate change, and pollution. Yellowstone Lake Area of Yellowstone National Park 3,472 mi2 (8,991 km2) Water surface area2,3 ~5% of park area Number of named lakes 150 1 Yellowstone Lake is the largest high-elevation lake (above 7,000 ft) in North America, covering up to 139 square miles, with an average depth of 138 feet, and just over 12,000,000 acre-feet of water. The lake is covered by ice from mid-December to May or June. Surface area of named lakes 24.7 mi2 (63.9 km2) Number of lakes with fish2 ~45 Number of named streams3 278 Total stream length3 2,172.52 mi (3,496,329 m) • Elevation: 7,731 feet (2,357 m) • Surface area: 131.8–135.9 mi2 (341–352 km2) ~200 • Perimeter (Shoreline): 141 miles (227 km) • Deepest point is due east of Stevenson Island at 430 feet (131 m) 1 Number of streams with fish2 Yellowstone Spatial Analysis Center data. Varley and Schullery 1998. 3 GRYN Water Quality Report 2009. 1 2 56 Yellowstone Resources and Issues Handbook, 2019 Yellowstone Lake Quick Facts So da B utte C r r d ner R iver i ver Ga eR Rive Firehole River ID ws ton r Gi b b o n Madison River MT lo Yel Shoshone Lake Lewis Lake West Yellowstone Lake Thumb Heart Lake Snake R Major watersheds Shoshone River Missouri River E CO S YS T E M Lewis Lake is fed by the Lewis River and other tributaries. Shoshone Lake, the park’s second largest lake, is located at the head of the Lewis River southwest of West Thumb. Shoshone Lake is a valuable wilderness resource. Only accessible by foot, or by boat through the Lewis River Channel, one of the park's amazing geyser basins lies near the northwest shore. Shoshone Lake is 205 feet at its maximum depth, has an area of 8,050 acres, and contains lake trout, brown trout (Salmo trutta), and Utah chub (Gila atraria). Originally, Shoshone Lake was barren of fish owing to waterfalls on the Lewis River. The two types of r MT WY ive ar R Lewis and Shoshone Lakes eek L am Entering Yellowstone Lake are more than 141 tributaries, but only one river. The Yellowstone River, which enters at the south end of the southeast arm, dominates the inflow of water and sediment flows out. The only outlet of the lake is at Fishing Bridge, where the Yellowstone River flows north and discharges 2,000–9,000 cubic feet per second. Powerful geologic processes in Yellowstone National Park have contributed to the unusual shape of Yellowstone Lake, which straddles the southeast margin of the Yellowstone caldera. A smaller calderaforming event about 174,000 years ago, comparable in size to Crater Lake, Oregon, created the West Thumb basin. Several significant glacial advances and recessions continued to shape the lake and overlapped the volcanic events. Glacial scour deepened the central basin of the lake and the faulted south and southeast arms. More recent dynamic processes shaping Yellowstone Lake include currently active fault systems, development of a series of postglacial shoreline terraces, and postglacial hydrothermalexplosion events, which created the Mary Bay crater complex and other craters. (See “Yellowstone Lake Geology” in chapter four, for more information.) Many of the area’s 1,000 to 3,000 annual earthquakes occur under Yellowstone Lake, causing uplift and subsidence events which continually reshape the shoreline of the lake. Yellowstone Lake is also the site of one of the most extensive conservation efforts in the National Park Service. Lake trout (Salvelinus namaycush) which were illegally introduced to Yellowstone Lake have jeopardized the survival of the native population of cutthroat trout (Oncorhynchus clarkii bouvieri). See “Native Fish Species” and “Lake Trout” in the wildlife chapter for more information. i v er 0 0 10 km 10 mi Snake River Yellowstone River trout were planted beginning in 1890, and the Utah chub was apparently introduced by bait fishermen. This large lake is the source of the Lewis River, which flows to the Pacific Ocean via the Snake River system. The U.S. Fish and Wildlife Service believes that Shoshone Lake may be the largest lake in the lower 48 states that cannot be reached by road. Heart Lake Heart Lake is located at the south end of the park near the base of Mt. Sheridan. It sits in prime bear habitat, and there are several thermal areas along the northwest shore. Rivers Watersheds, or drainage basins, represent the surface area that contributes runoff to a particular river. The boundaries of a watershed are ridges or elevated areas which determine the direction surface water will flow. Any rain or snow that falls within the watershed will flow downstream to the basin’s mouth, unless it is removed from the flow by evaporation, freezing, absorption as groundwater, or diversion for human use. Yellowstone River The Yellowstone River is 671 miles long. It is the longest undammed river in the lower 48 states. The headwaters of the Yellowstone are outside the Greater Yellowstone Ecosystem 57 corner of the park and flows to the Missouri River. The Gardner flows into the Yellowstone first, joining near Rattlesnake Butte at the north entrance to the park. E C O S YS T E M Snake River Yellowstone River delta southeast park boundary on Younts Peak (Wyoming) and flows into Yellowstone Lake. It leaves the lake at Fishing Bridge, and continues north-northwest until it leaves the park near Gardiner, Montana. The Yellowstone River continues north and east through Montana and joins the Missouri River just across the North Dakota state line. Its watershed drains onethird of the state of Montana. It carves out the Grand Canyon of the Yellowstone in the middle of the park and runs over the Upper and Lower Falls and is home to Yellowstone cutthroat trout. The Yellowstone River is among the top recreational river destinations in the US and provides opportunities for boating and fishing enthusiasts, birders, and for recreation. Additionally, the Yellowstone River serves many downstream communities (e.g., Billings, Montana) and is recognized regionally and nationally for economic importance to agriculture, industry, and municipalities. Lamar River The Lamar River originates on the east side of the park. Park boundaries were adjusted in 1929 to include the entire Lamar watershed in order to protect this major tributary of the Yellowstone River. The Lamar River is joined by Soda Butte Creek as it flows across the northern range to the outflow of Yellowstone Lake. The Lamar River Valley is home to wild pronghorn, bison rutting, bear habitat, the most consistent viewing of wild wolves in the world, and first-rate fly fishing. Gardner River The Gardner River originates in the northwest 58 Yellowstone Resources and Issues Handbook, 2019 The Snake River—a major tributary of the Columbia River—originates in Yellowstone National Park, and then turns south, passing through the John D. Rockefeller, Jr., Memorial Parkway into Grand Teton National Park. The river flows through Idaho and joins the Columbia River in Washington. The Snake River is 1,040 miles long (1,674 km); 42 miles (68 km) of it are in Yellowstone National Park. The river feeds Jackson Lake—a natural lake augmented by a dam, resulting in regulated downstream flows since 1907. Visitors enjoy a multitude of recreational opportunities on the river such as rafting, fishing, and photography. The river is home to a wide variety of riparian and aquatic species, including the native Yellowstone cutthroat trout and an endemic variety, the Snake River fine-spotted cutthroat trout (Oncorhynchus clarkii behnkei). The 2009 Snake River Headwaters Legacy Act designated the river above Jackson Lake as a Wild and Scenic River. The Lewis River is a tributary of the Snake River. Firehole River Home to several species of trout, the Firehole River is a favored fly fishing spot. Most of the outflow from the park’s geyser basins empties into the Firehole River causing it to be warmer with larger concentrations of dissolved minerals (chemically richer) than FREQUENTLY ASKED QUESTION Does the Missouri River begin here? No, but its three tributaries begin in the greater Yellowstone area. The Jefferson River begins in the Centennial Mountains, west of the park. The Madison River forms inside the park at Madison Junction, where the Gibbon and Firehole rivers join. The Gallatin River also begins inside the park north of the Madison River. It flows north through Gallatin Canyon and across the Gallatin Valley, joining the Madison and Jefferson rivers at Three Forks, Montana, to form the Missouri River. other watersheds. The Gibbon and Firehole rivers join to form the Madison River. The Madison flows to Hebgen Lake, joins the Jefferson River and eventually the Missouri River on its way to the Gulf of Mexico. Water Quality The quality of the nation’s waters is protected by laws and policy at local, state, and federal levels. To understand and maintain or improve water quality and aquatic ecosystems, resource managers take inventory and actively monitor water resources throughout the region. Water quality in a national park may reflect activities taking place upstream of the park’s surface waters as well as within the park. The water quality in Grand Teton and Yellowstone national parks, where most of the watersheds originate on federally protected land, is generally very A volunteer collects a water sample at Soda Butte Creek. Collection of water quality data has continued at fixed sites since 2002. Long-term Water Quality Monitoring Monitoring water quality continues to be a high priority for Yellowstone, with standardized data collected at fixed sites since 2002. This long-term data is used to evaluate overall ecosystem health, ascertain impacts of potential stressors (e.g., upstream impacts from legacy mines), identify changes that may be associated with water quality degradation, and guide resource management decisions related to water quality. The characteristics of Yellowstone’s surface waters are influenced by season, elevation, precipitation, and weather. Some waters are also affected by the park’s geothermal features, generally resulting in warmer temperatures and higher dissolved ion concentrations. Park staff monitors water temperature, dissolved oxygen, pH, specific conductance, turbidity, and total suspended solids at 11 stream sites and 7 sites on Yellowstone Lake. Staff collect chemical parameters from 10 stream sites, including anions, cations, and nutrients. Most waters in Yellowstone meet or surpass national and state water quality standards. Geothermal influence on some park waters can result in failure to meet state drinking or recreational water quality standards. For example, arsenic levels in the Madison River at West Yellowstone exceeded the State of Montana’s criteria on most sampling occasions. Arsenic in the Madison River is likely naturally occurring from geothermal geology in the watershed. Park staff also monitor three sites on the park boundary where stream segments in the Yellowstone River drainage have been listed as impaired by the State of Montana. Greater Yellowstone Ecosystem 59 E CO S YS T E M Fishing on the Firehole River. high. However, it is vulnerable to impacts such as road construction, recreational activities, and deposition from atmospheric pollutants. All Yellowstone waters are classified as Outstanding National Resource Waters, which receive the highest level of protection for surface waters under the Clean Water Act. Because of the relatively pristine nature of the park’s surface waters, they are often used to establish reference conditions for the northern Rocky Mountain region. Although most of the park’s watersheds originate within its boundaries and are minimally affected by human activities, they are vulnerable to impacts such as road construction, dewatering, atmospheric deposition, sewage spills, climate change, and runoff from mining sites outside park boundaries. Reese Creek E C O S YS T E M Irrigation by landowners north of the park has often reduced the lowermost reach of the stream during mid-summer and fall. The water flow becomes unsuitable for sustaining native trout and overall biological integrity. The adjudicated water rights stipulate that the creek is to have a minimum flow of 1.306 ft3/ sec from April 15 to October 15. A stakeholder group of federal agencies, private citizens, and conservation organizations are working together on projects to increase the flows in the main channel. Soda Butte Creek Soda Butte Creek is located near the park boundary, approximately 5 miles (8 km) downstream of the former location of the McLaren Mill and Tailings site. As a result of metal contamination from previous mining activity, dissolved and total metals (arsenic, copper, iron, and lead) persist in the floodplain. State and federal agencies completed a three-year effort to relocate mine tailings away from the floodplain and to reconstruct the former channel in 2014. Results from 2015 and 2016 monitoring activities in Soda Butte Creek downstream of the reclamation work show that iron levels associated with the former tailing site have been dramatically reduced. The resulting data from recent monitoring also led to a determination in November 2017 by the Montana Department of Environmental Quality (DEQ) that metals conditions in Soda Butte Creek support designated beneficial uses. Montana DEQ has now recommended removing Soda Butte Creek from the state’s impaired water 303(d) list. The 60 Yellowstone Resources and Issues Handbook, 2019 reclamation of McLaren Mill and Tailings site and subsequent removal from the 303(d) list represent important milestones in the restoration of Soda Butte Creek. Yellowstone River at Corwin Springs Similar to prior years, water samples were collected on the Yellowstone River from late February to early November 2017 and indicated that sites exceeded the EPA drinking water standard of 0.01 mg/L total arsenic but not the aquatic life criterion (0.15 mg/L). The higher total arsenic values in this drainage may be due to natural geological or geothermal influences on water chemistry. More Information Gude, P.H., A.J. Hansen, and D.A. Jones. 2007. Biodiversity consequences of alternative future land use scenarios in Greater Yellowstone. Ecological Applications 17(4): 1004–1018. Koel, T. et al. 2014. Yellowstone Fisheries and Aquatic Sciences Report 2012–2013. National Park Service: Yellowstone National Park. Levandowski, M. and A. Ray. 2017. Water quality summary for the Lamar River, Yellowstone River, and Madison River in Yellowstone National Park: Preliminary analysis of 2015 data. Natural Resources Report NPS/GRYN/ NRR-2017/1389. National Park Service, Fort Collins, Colorado. Marcus, W.A., J.E. Meacham, A.W. Rodman, A.Y. Steingisser. 2012. Atlas of Yellowstone. University of California Press. Staff Reviewer Andrew Ray, Ecologist, Greater Yellowstone Network. Jeff Arnold, Fishery Biologist. The ecological diversity of the Greater Yellowstone Ecosystem contributes to its value, and its controversy. Yellowstone's northern range has been the focus of debate since the 1930’s. Cycles and processes are essential connections within an ecosystem. Photosynthesis, predation, decomposition, climate, and precipitation facilitate the flow of energy and raw materials. Living things absorb, transform, and circulate energy and raw materials and release them again. Life forms are active at all levels. Microbes beneath Yellowstone Lake thrive in hydrothermal vents where they obtain energy from sulfur instead of the sun. Plants draw energy from the sun and cycle nutrients such as carbon, sulfur, and nitrogen through the system. Herbivores, from ephydrid flies to elk, feed on the plants and, in turn, provide food for predators like coyotes and hawks. Decomposers—bacteria, fungi, other microorganisms—connect all that dies with all that is alive. The ecosystem is constantly changing and evolving. A wildland fire is one example of an integral, dynamic process. Fires rejuvenate forests on a grand scale. Some species of plants survive the intense burning to re-sprout. Some cones of lodgepole pines pop open only in heat generated by fires, spreading millions of seeds on the forest floor. After fire sweeps through an area, mammals, birds, and insects quickly take advantage of the newly created habitats. Fires recycle and release nutrients and create dead trees or snags that serve a number of ecological functions, such as the addition of organic matter to the soil when the trees decompose. These cycles and processes are easily and frequently observed on Yellowstone’s northern range, which refers to the broad grassland that borders the Yellowstone and Lamar rivers in the northern portion of the park and into Montana. This area sustains one of the largest and most diverse communities of free-roaming large animals seen anywhere on Earth. Many of the park’s ungulates spend the winter here. Elevations are lower, and the area receives less snow than elsewhere in the park. Often, the ridge tops and south-facing hillsides are clear of snow, a result of wind and sun. Animals take advantage of this lack of snow, finding easier access to forage. As a result of its incredible biodiversity, relatively complete ecosystem integrity, and year-round access, research conducted on the northern range has informed much of our current scientific understanding of native species and the ecological processes that sustain them. Biodiversity Each species—no matter how small—has an important role to play in a functioning ecosystem. They all participate in various ecosystem processes like transferring energy, providing nutrient storage, or breaking down pollutants. That is why biological diversity, or biodiversity, is a benchmark for measuring the health of an ecosystem. Biodiversity can be measured in many ways, including the number of different species (also called richness) and the abundance of each species (also called evenness). The biodiversity and ecological processes that are protected in the park support a healthy ecosystem. Significantly, Greater Yellowstone’s natural diversity is essentially intact. The region appears to have retained or restored its full historical complement of vertebrate wildlife species—a condition unique in the wildlands of the contiguous 48 states. The extent of wildlife diversity is due, in part, to the different habitats found in the region, ranging from high alpine areas to sagebrush country, from hydrothermal areas, to forests, meadows, and other habitat types. All of these are connected, by landforms, through links provided by streams and rivers that course through the changing elevations, and by the air that circulates between them. Greater Yellowstone Ecosystem 61 E CO S YS T E M Cycles and Processes Gardiner Mammoth Hot Springs Yellowst on e La m ar Ri v er E C O S YS T E M ver Ri Tower Junction = Yellowstone's northern range The northern range is a broad grassland that borders the Yellowstone and Lamar rivers in the northern portion of Yellowstone and into Montana. Biodiversity also supports the resilience of an ecosystem. When a variety of organisms contributes to ecosystem processes, an ecosystem can be more flexible through dynamic events like floods or fire. Knowledge of the park’s biodiversity expanded in 2009 with Yellowstone’s first bioblitz. Intricate Layers The reintroduction of the wolf to Yellowstone restored an important element of ecological compl