Killer on the open range

The road tracing the northern edge of Red Rock Lakes National Wildlife Refuge cuts through sand dunes in a sea of sagebrush about 80 miles south of Ennis. Basin big sagebrush, Artemisia tridentata to be exact, is a marvelous species known to grow up to 13 feet tall. Most of the basin big sagebrush around Red Rock Lakes in the Centennial Valley appear to top out around six feet, which makes them tall enough to poke through the snowpack in winter. 

That’s important because the sage grouse wintering in the Centennial Valley depend on the plant’s pale, gray-green foliage. 

“They rely almost exclusively on that for their diet. They eat the edges of the leaves,” explained James Waxe, who manages conservation and research projects in the Centennial Valley for The Nature Conservancy. 

Back in 2017, Waxe witnessed the start of a murder mystery involving the basin big sagebrush as huge swaths of this iconic plant started dropping dead. 

The die-off continued into 2021, said Waxe, impacting “well over 10,000 acres.” Now big pieces of the Centennial Valley’s sagebrush range appear to be lifeless zones with thousands of basin big sagebrush standing dead and dry. Waxe said the sagebrush in the impacted areas were 50-80 years old when they died. 

Today, the dead sagebrush look like bodies littered across a 10,000-plus acre crime scene.

The killings, said Waxe, appear to be an inside job. 

“I do want to make it clear that the insects that are killing this plant are both native,” said Waxe. “We have two hypotheses and, and we really never figured out exactly what it was. But talking with entomologists it could be Aroga moths, that’s a defoliating moth. Or a flea beetle is the other one. It’s likely one of the two, if not both.”

The sagebrush defoliator moth (Aroga websteri) is a small but mighty serial killer, according to research from the U.S. Forest Service and Bureau of Land Management. This micro-moth species causes extensive damage to sagebrush communities through the feeding habits of its larvae.

During severe outbreaks, a single sagebrush plant may host over 66 larvae, resulting in complete defoliation. High populations of these moths can strip a sagebrush plant bare in just one season, often leading to plant death within a year.

The defoliation process is particularly harmful as it deprives the plant of its ability to photosynthesize and produce energy. This makes the sagebrush vulnerable to other environmental stressors such as drought and harsh winter conditions.

The moth’s population dynamics appear to be closely tied to weather patterns. Years with high precipitation in June and July, coinciding with late-stage larval development, can lead to population explosions.

Older plants are particularly susceptible, with large percentages succumbing to severe infestations. However, younger, more vigorous plants often show resilience and can recover from defoliation.

Some ecologists suggest that the sagebrush defoliator moth may play a role similar to fire in maintaining diverse age structures within sagebrush communities.

“They behave much like pine beetles do where they come in and they kill a lot of plants if not all of them in large stands and then they won't come back for a long time,” said Waxe. 

As for flea beetles, the other suspected killer of basin big sage, there’s less known about how this insect dispatches sagebrush plants. In other plants, flea beetles are known to eat holes in leaves, while also devouring root hairs, a combination that deprives plants of nutrients while making it harder to photosynthesize. 

As you drive along North Valley Road on the boundary of Red Rock Lakes NWR, the route bobs through the sand dunes and healthy expanses of sagebrush. Then you come over a rise and suddenly it’s clear something’s different. Whole swaths of basin big sagebrush change from healthy, verdant expanses to huge patches of gray and lifeless stalks. The dead basin big sagebrush sway in the wind surrounded in early fall by yellow blooming rabbit brush. 

Driving through healthy-then-dead tracts of sagebrush feels like botanical whiplash. Realizing all the sagebrush around you are dead creates an awkward record scratch moment that brings the otherwise blissful experience of traveling through the open range to an abrupt end. 

For a long time now, writers covering the West have issued warnings about taking sagebrush for granted. In a 2018 article for “Camas: The Nature of the West,” writer Marko Capoferri offered his “Ode to Sagebrush Country.”

Capoferri observed, “Where sagebrush is most prolific is also where you’ll find the fewest people.”

Waxing poetic, Capoferri continued, “Sagebrush Country: it feels limiting and limitless all at once, a collision of thwarted desire and inspired longing in a vast, arid space. Sagebrush Country is enticing in its liminality, in the incoherent frictions that spark a sublime fire in the open mind.”

Liminality is a state of transition or flux that can be experienced in many contexts, including rites of passage, learning journeys and major life transitions. 

Or during a bumpy ride through massive swaths of sage, some living, some dead.

Back in 2015, a Washington Post headline wondered aloud: “The Western sagebrush is a backdrop in every epic cowboy movie. Can it be saved?” 

This story by journalist Darryl Fears documented the start of conservation work that continues today. 

Fears talked to Len Barson with The Nature Conservancy, who said, “The sagebrush is really a part of Americana and a part of history that people in the West are living. You take a look at history—and sagebrush is there. You have the railroad, you have the Oregon trail, ranches and cattle drives, the tumbleweed going across the road, the old cowboy movies. It’s sort of ingrained in our soul a little bit, this image of the wild West and what that meant to America.”

To sagebrush watchers like TNC’s Waxe in the Centennial Valley, the basin big sagebrush remains the resilient sentinel, anchoring an ecosystem and scenting its surroundings after rain. 

Waxe said the die off of basin big sage has, “Drastically slowed down. And it didn’t kill everything. There are islands of live mature sagebrush that did not get killed.”

Still, said Waxe, “Sagebrush in general is threatened by human development. Across the American West we’ve lost at least 56% of sagebrush cover since the early 1900s.”

“Down in Nevada where there's lots of basin big sagebrush, they witness a lot of big epizootic events where they see large die-offs of the basin big sagebrush,” said Waxe, describing how life eventually returns to these areas.

In the Centennial Valley, said Waxe, another sagebrush species is opportunistically appearing inside the dead zones. 

“The three tip sagebrush (Artemisia tripartita) is already kind of filling in the gaps,” assured Waxe. “And we have actually noticed quite a few sprouts of basin big sagebrush coming back in.”