North America’s Sagebrush Habitat is Disappearing
Written by Quentin Septer
Note: This is a modified excerpt from my book, Where Land Becomes Sky: Life and Death Along the Colorado Trail, available now.
Sunlight cascades down mountains to the west, and the forest comes alive with avian hymns. Rising, I leave the shadows of the woods and hike a few hundred yards up the mountainside, where the morning sun shines warmly on thickets of silvery blue sagebrush. Cattle graze among the sage, eying me wearily as I sit in the sun, writing in my Moleskine and drawing sketches of the rust and ivory and black colored ruminants against the backdrop of the Gunnison Basin, now miles away and thousands of feet downslope. Black-billed magpies flutter about aspen and evergreen canopies above the cattle, belting out coarse calls that reverberate throughout a still and quiet forest.
The corvids rise and fall, from the floor of the meadow to the branches of trees and back again. Against a green screen of quaking aspen crowns, a magpie stretches its wings with the sweeping motion of an unfurling Chinese hand fan. Metallic blue feathers gleam in the rising sun. The bird’s back, nape, and crown are colored a deep, obsidian black, enclosed by two bright white, half ovals at the base of its wings. The bird’s long and prominent tail feathers bear a shade of indigo. Its wing feathers wear hues of navy blue. Its outer wings: a pure shade of white, outlined by inky black feather tips. From a nearby pine, a magpie glides to the spine of a grazing cow. The bird lands on the cow’s back, perches and picks at something in the ruminant’s jet black hide.
Before Europeans brought cattle to the Americas, magpies lived among the buffalo. They forged a symbiotic relationship, the magpie and the buffalo. Ticks and other insects embedded in the hides of the bison provided a steady food supply for the magpies, who removed the pests from the massive ungulates. Today, with the buffalo extirpated from ninety-nine percent of the species’ native range in North America, the magpie occupies a similar niche among cattle.
I sit and watch the birds and the cattle eating their respective breakfasts of insects and grass. I eat a Clif bar and a few handfuls of dried fruit, myself. Downslope, sageland spreads toward the floor of the Gunnison Basin, where irrigated pastures and bunches of cheatgrass stain the landscape muted yellow tones. The cheatgrass has grown dry and brittle in the wake of a long, hot summer. The basin stretches toward a hazy horizon, where altocumulus clouds drift gently to the east, throwing shade upon golden hills.
As beautiful as it is, the view before me emblemizes an often under-appreciated ecological issue here in the American West: sagebrush is disappearing.
Sagebrush. Big sagebrush. Big mountain sagebrush. Great Basin sagebrush. Artemisia tridentata. It’s a modest shrub with silver-blue, needle-like leaves and a pungent, aromatic scent. If you’ve spent any time in the western United States, you’ve probably seen a good deal of it. Historically, much of the Intermountain West was characterized by an ecosystem called the sagebrush steppe. Imagine, if you will, a seemingly endless expanse of high country desert, studded with sage, rolling on toward distant mountains and a big, blue sky. The sagebrush steppe looks something like that. But it’s far from a monoculture of mere shrubbery.
Several subspecies of sagebrush exist. And sagebrush provides habitat to dozens of fellow plant species, dozens of mammal species, more than a hundred species of birds, hundreds of species of invertebrates, thousands of insects, and several endangered species across the Intermountain West. Among them is the greater sage-grouse, the population of which has declined by more than a third since 1985. “Historically,” a report from the Forest Service’s Rocky Mountain Research Station reads, “sage-grouse occurred in 16 states and 3 provinces from British Columbia east to Saskatchewan and south to Oklahoma and California. In 2016, they occured in 12 states and 2 provinces and their distribution was discontinuous.”
“Sage-grouse once occurred virtually everywhere there was sagebrush,” the report continues. Today, the greater sage-grouse occupies an area about half the size of its historic range, prior to the Euro-American settlement of the West.
Since 1965, approximately 80 percent of North America’s sage-grouse have disappeared. The Gunnison sage-grouse — a smaller subspecies of the greater sage-grouse — has been extirpated from more than 90 percent of its native range over the same period. The species occupies a portion of southwestern Colorado, as well as an adjacent part of Utah. The United States Fish and Wildlife Service estimates that five thousand of the birds remain in the state, all of whom in a handful of isolated, vulnerable populations. An estimated 86 percent of remaining Gunnison sage-grouse live in the Gunnison Basin, for which the species was named. In 2013, officials from the USFWS reported a population of 3,149 Gunnison sage-grouse in the region. By 2020, the population had dwindled to 1,667 — a 40 percent decline in six years. The Gunnison sage-grouse was listed under the Endangered Species Act in 2000, and still, the birds continue to vanish. In 2013, a total of 848 males were documented on “leks,” or nesting grounds, in the Gunnison Basin. By 2019, this figure dropped to 363 males.
Sage-grouse are known as “sagebrush-obligate species,” among ecologists. Plainly, these species — sage grouse, sage thrashers, sagebrush sparrows, and Brewer’s sparrows, among others — need healthy sagebrush habitat to survive. “Sagebrush is the single most important item in the adult sage-grouse diet year-round,” to draw again upon the words of officials from the Forest Service’s Rocky Mountain Research Station. Sagebrush also provides the birds with mating habitat, shelter from the elements, and winter nesting grounds.
“The greater sage-grouse is a sagebrush obligate species whose populations generally track declines in sagebrush, and is highly influential in shaping state and national use policy.” These are the words of researchers from the United States Geological Survey and the United States Fish and Wildlife Service, writing in a 2016 study published in the Proceedings of the National Academy of Sciences. The paper was lead-authored by Peter S. Coates, a wildlife biologist with the U.S.G.S. “If wildfire trends continue unabated,” the paper continues, “model projections indicate sage-grouse populations will be reduced to 43% of their current numbers over the next three decades.” Sagebrush isn’t simply disappearing, you see, it’s going up in flames. The sagebrush steppe has been burning and otherwise declining so rapidly over the last century, in fact, that researchers writing in Western Birds have deemed sagebrush habitat “one of North America’s most imperiled ecosystems.”
Across the West, the sagebrush steppe has been fragmented and disrupted. Sagebrush habitat has been overgrown with nonnative species like cheatgrass, overgrazed by cattle on both public and private land, plowed up and replaced by ranchlands, roadways, and cityscapes. Prior to the European settlement of North America, the sagebrush steppe occupied some 375 million acres across the western United States. Today, America’s remaining sagebrush habitat spans an area about half that size. The Bureau of Land Management (BLM) estimates that over 60 percent of the “pre-Columbian sagebrush steppe has been invaded by exotic plants, changing its structure.” And some of these changes in the structure of the sagebrush steppe have made these ecosystems more flammable.
The sagebrush steppe, like any other terrestrial ecosystem, burns at historically predictable intervals. It’s what’s known as a “fire interval” in ecology — how often a landscape tends to go up in flames. Traditionally, the sagebrush steppe of the American West burned once every 30 to 80 years, on average. Some sagebrush ecosystems burn more frequently, others less so, depending on factors like soil moisture and local temperatures, plant communities, weather, topography, among other variables influencing a landscape’s combustibility. When invaded by cheatgrass, sagebrush ecosystems burn much more frequently — once every three to five years, on average. And on freshly fire-scorched portions of the sagebrush steppe is where the issues of cattle grazing, invasive species the likes of cheatgrass, and vanishing sagebrush habitat become more deeply intertwined.
As cattle waddle across the landscape, they accumulate and carry seeds on the soles of their hooves, which they go on to plant elsewhere in the soil with a ponderous hoovestep. A species with an uncanny knack for hitching a ride on the underside of cattle hooves is cheatgrass — Bromus tectorum. A native grass of Eurasia, cheatgrass is thought to have been introduced to North America in contaminated grain shipments brought to the United States in the mid-1800s. The species was first documented on the east coast in 1861; first seen on the west coast in the concluding years of the nineteenth century. In the words of the late conservationist Aldo Leopold, writing in his seminal work, A Sand County Almanac:
Today the honey-colored hills that flank the northwestern mountains derive their hue not from the rich and useful bunchgrass and wheatgrass which once covered them, but from the inferior cheat which has replaced these native grasses.
“If you had to pick just one,” ecologist and science writer Jonathan Thompson wrote, “cheatgrass invasion is perhaps the greatest threat to sagebrush habitat.” Cheatgrass spreads like wildfire. In just over 150 years, the species has diffused far and wide across the western United States, covering an estimated 100 million acres. And cheatgrass spreads with a special kind of tenacity on the sagebrush steppe. The species burns much more frequently than sagebrush, and the fast-growing grass grows with vigor in freshly charred soils. Thus, in the wake of wildfire, invasive grasses like cheatgrass tend to crowd out native, slower-growing plants like sagebrush, as well as bunchgrass and wheatgrass, among other species indigenous to the North American continent. It’s an insidious kind of feedback loop: as more cheatgrass intrudes upon America’s sagebrush steppe, and as wildfires blaze more frequently on these landscapes, cheatgrass replaces sagebrush ever more swiftly. “Where nonnative annual grasses such as cheatgrass have established and spread,” officials from the Forest Service write, the landscape has been supplied with “continuous fire-fuels,” and “sagebrush communities are more likely to reburn before sagebrush has recovered.” Peter Coates and his colleagues call this relationship among sage and cheatgrass “a novel disturbance cycle of wildfire and annual grass invasion.” Every year, about 2 million acres of sagebrush goes up in flames on BLM lands alone. And often, the sage is replaced by cheatgrass and other invasive grass species.
The disappearance of sagebrush isn’t a simple matter of aesthetics, however. With the loss of sagebrush habitat comes the loss of species dependent upon that habitat for survival. Back in 2016, Peter Coates and his colleagues at the U.S.G.S. and the U.S. Fish and Wildlife Service looked into the future of North America’s sagebrush steppe and its resident sage-grouse. Using Bayesian statistical analyses, the researchers analyzed rates of cheatgrass intrusion upon sagebrush habitat, rates at which wildfires burn on the sagebrush steppe, rates of sagebrush dehabitation in the wake of wildfire, and rates at which sagebrush-obligate species are declining in numbers in response to these losses in habitat. Then they projected these trends three decades into the future. Specifically, Coates and his team focused on greater sage-grouse populations in the Great Basin — a sea of sagebrush occupying much of Nevada, Oregon, and Utah, along with parts of California, Idaho, Wyoming, and Baja California, Mexico. The results of the study, however, speak to declining sagebrush habitat and declining sage-grouse populations seen more broadly across the western United States.
By 2044, Coates and his team found, sage-grouse populations are expected to more than halve in size. Other sagebrush-obligate species — sage sparrows and sagebrush thrashers among them — face similar declines in coming decades, the populations of which have been plummeting since the 1960s. By 2050, America’s sagebrush steppe — greater sage-grouse nesting habitat, in particular — is projected to shrink 12 percent relative to habitat area documented in 2005, according to data published in Ecological Indicators.
Sage-grouse are considered “keystone species” on the sagebrush steppe. The health of the ecosystem is implied by the health of resident sage grouse populations. And it’s work the likes of Coates’ and his colleagues’ that informs land managers at agencies like the BLM of a given ecosystem’s health. Confronted with the data, land managers across the Intermountain West have worked to restore America’s fleeting sagebrush habitat. They’ve planted sagebrush seeds. They’ve treated swaths of cheatgrass with herbicides. And, ironically, they’ve grazed livestock on the sagebrush steppe (the circular logic being that the more cheatgrass livestock eat, the less cheatgrass will be left on the landscape). Land managers have also implemented prescribed burns to control cheatgrass invasion on the sagebrush steppe.
Still, sagebrush habitat continues to decline.
Cheatgrass continues to spread.
The cattle and the magpies before me, the cheatgrass and the sagebrush beneath my feet — all signify, to my mind, the interdependence of all species on the landscape. Implied by these species, too, is how landscapes change over time, often so slowly that we fail to notice any changes at all. “There is, as yet, no sense of pride in the husbandry of wild plants and animals,” Aldo Leopold wrote of our relationship to cheatgrass and other invasive species that wreak havoc on North American ecosystems. And there is, as yet, “no sense of shame in the proprietorship of a sick landscape,” Leopold went on to say. The man wrote these words in the 1940s, mind you.
Trekking back to my tent, among sagebrush and cheatgrass, cattle and magpies, I’m left wondering if some things ever change.