by Delia Malone
Wolves represent wilderness. Colonizers viewed wilderness as a frontier to be conquered and converted into a landscape that mirrored Europe. This meant that wolves had to go. So, as Michael Robinson writes in Predatory Bureaucracy, wolves were killed with a vengeance not experienced by any other wildlife species — a vengeance that continues today in much of the United States.
Just as Aldo Leopold originally believed that “because fewer wolves meant more deer, no wolves would mean hunter’s paradise,” A common refrain among ranchers is, “There’s a reason that we got rid of the apex predator in the first place.” Yes, without wolves on the landscape, ranchers could graze their livestock without human supervision, but unforeseen and far-reaching ecological changes resulted from both wolf extirpation and unmanaged livestock grazing.
Mitochondrial DNA evidence implies a population of around 400,000 wolves in the western U.S. and Mexico since the last glaciation and prior to European expansion. In just a few short decades, between the 1880s and 1920s, the war on wolves had all but exterminated them from the lower 48 states. The rapid loss of this ecological keystone carnivore reverberated throughout the landscape.
Preceding the extirpation of wolves, there was the market-hunting-driven loss of native ungulates followed by severe overstocking of the range with livestock. In response to the demise of native prey, wolves turned to livestock for their prey. In response, the livestock industry used its political clout to fund a state bounty system to trap, hunt, and kill wolves. As Robinson has documented, only a handful of lone wolves survived into the 1930s and ’40s. The widespread use of strychnine was the wolf’s death knell. Poisoned animal carcasses were left out for wolves, and those carcasses also killed eagles, ravens, foxes, bears, and any animals that fed on the poisoned carrion. In Colorado wolves were functionally exterminated by 1900. According to Robinson, Colorado’s last wolf, Lobo, was killed in 1945 in Conejos County.
Data from Rocky Mountain National Park shows that market hunting had generally eliminated elk by 1880. Yet, wolves and other predators were designated a threat to big game and targeted for elimination. Gray wolves, the only significant predator of elk in the region, were largely absent from Colorado by 1900. In 1915 when Congress designated Rocky Mountain National Park, wolves were gone, other apex predators had been greatly reduced in number, and elk from Yellowstone had to be introduced to the park. Today in Rocky Mountain National Park, elk management practices seek to restore the ecosystem by substituting wolves with human interventions. But as demonstrated by a study published in 2014, this “functionalist” strategy substitutes the role of wolves in the ecosystem with human intervention and implicitly conflates the role or function of wolves with wolves themselves.
In his book The Wilderness Hunter, Theodore Roosevelt referred to wolves as “the beasts of waste and desolation.” As he learned more about North American predators, Roosevelt’s opinions changed, but his statement represented the prevailing view of the early 1900s in Yellowstone National Park. As a result, wolves were eliminated from the Park by 1926. Even though elk were still preyed upon by cougars and bears, a 2003 article by Douglas Smith et al., “Yellowstone after Wolves,” shows that the absence of wolves in Yellowstone took huge predatory pressure off elk, resulting in increased browsing on key forest species such as aspen and cottonwood as well as willow shrublands. Increased browsing pressure resulted in the decline of these forests and shrublands, impacts which rippled throughout Yellowstone’s ecosystems.
As documented in multiple studies, aspen forests are one of our most species-rich Rocky Mountain ecological systems, supporting numerous other organisms with a greater variety of plant associations than the typical conifer forests as well as increased bird species richness and total abundance. Yellowstone’s declining aspen ecosystems also result in diminished biodiversity, broken ecosystem connections, and altered system processes. Yellowstone ecosystems not only responded to the absence of wolves but to their return — i.e., species relationships changed with their absence and reciprocally with their restoration.
“Rewilding the American West,” a 2022 paper published in Bioscience, demonstrates that, as an apex predator, wolves can trigger strong ecological effects on prey and plants across a variety of landscapes of western North America, including aspen forests. With the restoration of wolves and a corresponding increase in the abundance of cougars and grizzlies in Yellowstone National Park, the elk population was appropriately reduced, and their behavior changed.
Smith et al. demonstrate that, instead of remaining stationary in the winter and overbrowsing aspen, cottonwood, and willow near streams, elk responded to wolves by moving around, which mitigated ecosystem damage, especially in riparian zones. Aspen began regenerating for the first time since wolf extirpation in 1926.
Wolves make landscapes healthier by keeping elk populations within ecological carrying capacity so that vegetation thrives. Regenerating woody vegetation provides habitat for other species, reestablishing ecosystem connections and re-enabling system processes such as nutrient cycling and energy flow. As the Smith study shows, aspen forests and riparian woodlands and shrublands regenerated after elk browsing pressure decreased. As a result, songbird diversity increased, beavers returned, and stream health is recovering. Wolves initiated a trophic cascade that restored ecological connections and relationships.
A recently published long-term study (1998-2021) of aspen recruitment in Yellowstone shows that restoration of large carnivores in the late 20th century resulted in a sustained reduction of Rocky Mountain elk and their overbrowsing, which facilitated new growth of quaking aspen saplings. Researchers found that both aspen saplings (≥2 m tall) and small trees were absent in 1998 but increased rapidly after 2007 to a mean density in 2020-21 of 1,460 small trees per hectare and that 43% of stands contained a new cohort of small trees (5-10 cm dbh), the first documented recruitment of overstory aspen trees in northern Yellowstone since the 1940s.
Across the Intermountain West, aspen forests are hotspots of biodiversity. In Colorado, there are more aspen forests than in any other state in the West, covering 5 million acres, more than any other forest type in Colorado (20% of Colorado’s forested land). As demonstrated by Kouki et al., because aspen forests cover a large area and provide refuge for a high diversity of native species, their protection provides outsized capacity for influencing regional and continental biodiversity.
But across the West, aspen stands have recently shown substantial decreases. Multiple studies show that primary threats to aspen ecosystems include fire suppression, drought-triggered mortality, chronic browsing of young aspen shoots by elk (resulting from a decrease in natural predators), and livestock.
Bird species diversity is high in healthy aspen forests. Conversely, where aspen stands in the southwest U.S. are in decline, bird diversity has decreased. About a third of all American bird species are of high or moderate concern due to low populations, declining trends, or other threats. Because aspen ecosystems and even small patches of aspen provide habitat for a disproportionately high number of bird species, protecting and conserving aspen forests and woodlands warrants conservation focus and is important to preventing continued declines.
Aspen woodlands are centers of bird abundance and diversity, but a 2017 U.S. Geological Survey report shows that they have been adversely affected by land-use practices, particularly livestock grazing. Likewise, a 2022 study by Ripple et al. demonstrates that retirement of grazing allotments within potential reserves offers great benefits for biodiversity.
Contemporary forest management needs radical re-visioning to stewardship that relies on native species and processes to restore ecosystem function and health. Grazing-allotment retirement provides a strategy for rewilding the landscape to restore native biodiversity to its rightful place in the self-management of wild populations guided by a complete suite of native carnivores, especially gray wolves.
Delia Malone is an ecologist with the Colorado Natural Heritage Program (retired). She is also the founder and president of ColoradoWild, wildlife chair for Colorado Sierra Club, and vice chair of Roaring Fork Audubon. As a field ecologist for the past 30 years, she’s conducted ecological assessments and biological surveys across Colorado. These decades of ecological and biological analyses have informed Malone’s purpose and demonstrated the need for protecting and restoring native wildlife and plants to Colorado wildlands. When she isn’t conducting field surveys, you can find Malone hiking, skiing, snowshoeing, or birding.
Photo: A wolf surveys its territory from a ridgetop in the Rocky Mountains.
