High Desert Dominator

High Desert Dominator header image
Western juniper covers 10 times more land than it did in the 1880s, and that has ranchers and ecologists concerned.

Western juniper is a familiar sight across the shrubby plains of eastern Oregon. Its dark green masses punctuate a landscape of silvery sage, golden grasses, and tan desert soil.

You can’t tell from a casual glance, but there’s a lot more juniper on the range than there used to be. It now occupies about 10 times more territory across eastern Oregon, northern California, and southwest Idaho than it did in the 1880s and has muscled out native shrubs, flowers, and grasses to achieve a dominance that may last for hundreds of years.

That’s bad news for Oregon’s high-desert ecology, says Rick Miller, an Agricultural Experiment Station scientist at the Eastern Oregon Agricultural Research Center (EOARC) in Burns. Since the late 19th century, when spreading European-American settlement coincided with a shift toward a warmer, moister climate, western juniper has spread across 9 million acres, according to Miller, and considerably more acres have the potential for being encroached.

What’s so bad about juniper? The main thing is that it hogs water, which is scarce to begin with in this environment where only 12 to 14 inches of precipitation fall each year. Its roots reach wide and deep, depleting water from the soil, and its heavy canopy can keep some precipitation from ever reaching the ground.

As juniper consumes more of the water and nutrients on a site, other plants languish and die—“a slow strangulation,” in the words of one eastern Oregon rancher. Lost are the nesting habitats for birds such as the western sage grouse, and gone is much of the food for large herbivores like mule deer, antelope, and elk. The bare soil washes away with every rainstorm, and eventually the land degrades to the point where it can support juniper and not much else.

Juniper is a hardy, prolific, adaptable, long-lived tree. Unlike troublesome exotic weeds such as medusahead and cheatgrass—both of which arrived after European-American settlement—western juniper is a native. It migrated north into its current range around 6,000 years ago, as the earth was warming after the last Ice Age, and shares the landscape with sagebrush and native grasses.

Juniper tree. Photo by Lynn Ketchum

Western junipers can live for centuries, becoming gnarled and spiky with spots of bright green lichen. Photo: Lynn Ketchum

Why is it so aggressive now? The main reason, says Miller, is fire—or, more accurately, lack of fire. Before European-American settlement, periodic fires tended to keep juniper in its place. The fires, ignited by lightning and by Native Americans, killed young juniper, invigorating a new flush of grasses and wildflowers.

Rick Miller. Photo by Lynn Ketchum   Tree sampling. Photo by Lynn Ketchum

OSU ecologist Rick Miller takes a core sample from a western juniper to read history from the rings of a tree. Photo: Lynn Ketchum


Using tree ring samples along with old surveys, photographs, and the distribution of old trees, Rick Miller is mapping the rapid expansion of western juniper. Photo: Lynn Ketchum

The frequency of fires dropped off dramatically in the late 1800s, after European-Americans settled the West. With cattle grazing the range, there was less fuel to burn and carry flames. The fires that did ignite were quickly suppressed by settlers. Lots of juniper seedlings took root, and these trees are now approaching maturity, poised to take over millions of acres of rangeland. Global climate change may also enhance juniper’s competitive ability, with higher levels of carbon dioxide in the atmosphere and warmer temperatures possibly pushing juniper into new territory farther uphill and to the north.

Invading juniper is not a new story, but its ecological significance is a fairly new concern. Until two or three decades ago, juniper was regarded as a cattle rancher’s problem. More juniper meant less forage for cattle, and ranchers got rid of it in any way they could. Some of the remedies were crude—such as slinging a 100-yard-long anchor chain between two bulldozers and dragging across a swath of trees. Through the 1970s and ’80s, scientists began to see invasive juniper as a larger ecological problem. Researchers such as Miller documented how it was changing the basic processes of the desert ecosystem—the cycling of water and nutrients, the stability of the soil, and the dynamic balance of plants growing in a marginal environment.

“The sagebrush biome is one of the biggest in the continental United States,” says Miller, “and it’s one of the most endangered,” impacted by exotic weeds and poor grazing practices, as well as by the artifacts of settlement: highways, houses, ranchettes, and drilling for gas and oil. The invading juniper, he says, “is one more significant hit on a biome that’s already in trouble.”

Western juniper grows readily from seeds dropped by birds. When it gets established, it follows a distinct successional path, moving from new arrival to cooperator to dominator in a predictable progression. At first, the trees are young and widely scattered, and sagebrush and grasses dominate the community. When the trees reach 45 to 50 years old, the understory of shrubs and grasses begins to decline. When trees are between 80 and 120 years old (perhaps older on some sites), the juniper has become so dominant that there isn’t enough left of the understory community to reestablish even if the trees are removed. Moister sites on north slopes may lose the shrubs but keep the grasses; sites on hotter south slopes may lose both shrubs and grasses and some of the soil, too. But if kept in check by wildfire or active management, natural communities of juniper, sage, and bunchgrass can provide food and shelter for a rich diversity of wildlife, including 83 species of birds and 23 species of mammals.

A small minority of juniper stands are truly ancient, 1,000 or more years old. These are growing mostly on sites naturally shielded from fire—rocky ridges and volcanic soils with not much other vegetation. These ancient woodlands make up about 10 percent of the total across most of its range, and they’ve long achieved a steady state. It’s the other 90 percent still in transition that concern Miller and his colleagues.

Western juniper 1890
Western juniper 1989

Photos taken about 1880 (top) and 1989 (bottom) show the encroachment of western juniper east of Prineville. Courtesy: Stu Garrett

Tools to confront the juniper invasion are chainsaws and prescribed fire, often followed by seeding of native plants. When trees are young, intervention is cheap and easy. “You can burn, if there’s enough fuel, or you can cut small trees,” says Miller. After treatment, the grasses and shrubs on the site have a good chance of regaining dominance.

When juniper is 50 years or so, it begins to beat out its neighbors, and halting it is more expensive and difficult. “You may have to cut bigger trees and more of them,” Miller says, “and there may not be enough fuel on the site for burning.” As juniper approaches 100 years old, it’s unlikely that the site will return to a shrub- and grass-dominated community without a major wildfire. A combination of mechanical treatment, prescribed fire, and seeding of the site might accomplish the task, but it’s an expensive intervention at this point.

Exotic weeds present a risk. Sometimes the desired native vegetation comes back after the juniper is taken away; sometimes it doesn’t. “If you have good stuff in the understory before removing the juniper, generally you’ll have good stuff afterward,” says Miller. But if you don’t have the good stuff, or if the site is particularly dry or warm, or if it faces south, or if it isn’t seeded immediately with desired grasses or shrubs, or if the manager has misjudged the juniper’s successional phase—or if a half-dozen other factors are not just right—cheatgrass or medusahead weeds may gallop in and leave the site worse off than before.

Fred Otley. Photo by Lynn Ketchum   Western juniper in winter. Photo by Rick Miller

Harney County rancher Fred Otley and his dog Pepper examine a pile of juniper cleared from Otley’s ranch. Photo: Lynn Ketchum


With age, western junipers often develop rounded tops and large lower limbs with deeply furrowed bark. Photo: Rick Miller

“You can be a winner more times than a loser, but you’re going to lose sometimes,” Miller says. “The risk of a poor outcome greatly increases when juniper is too abundant, the understory plants too feeble, or the soil too degraded. There are just too many interconnecting variables.”

To weigh the risks accurately, Miller asks, “What are the consequences of doing nothing? That’s just as much of a management decision as doing something. What will the site look like in 20 years if we don’t treat it?” Managers can greatly increase their success rate by asking the right questions: What is the goal? What is the problem? What plants or soils are on the site now? What course of treatment will be both affordable and effective? What follow-up will be needed?

Since the mid-1980s, rancher Fred Otley has been restoring juniper-dominated rangelands on his 16,000-acre ranch on the north side of Steens Mountain. The vast, sparsely settled area is a mix of private ranches and public rangeland managed by the U.S. Bureau of Land Management. Miller and colleagues, including Jon Bates and Tony Svejcar of the USDA Agricultural Research Service, have conducted many studies at the Otley ranch. Their results are helping Otley and his neighbors develop effective strategies for large-scale restoration projects. Otley, a fourth-generation Harney County rancher, says that the researchers at OSU’s experiment station have helped neighbors pull together to accomplish big projects that span boundary lines.

For example, about 30,000 acres have been treated with fire or cutting or both, and another 200,000 acres will see some form of treatment in the future, Otley says. “The planning has expanded to the whole area, and pretty much everybody is involved.” In addition, small niche markets have been developed for juniper wood, from specialty lumber for furniture and structural accents to fuel for generating electricity.

Mountain bluebirds. Photo by Rick Vetter   Soil erosion. Photo by Rick Miller

Mountain bluebirds are among at least 12 species of birds that feed on juniper berries and help disseminate seeds. Photo: Rick Vetter


Where junipers dominate a site, soil can be so impoverished that little else will grow. Photo: Rick Miller

Miller and several EOARC colleagues have recently compiled the current state of the science in a new book, Biology, Ecology, and Management of Western Juniper, published last year by the Oregon Agricultural Experiment Station. In addition, Miller and other landscape scientists from across the West are involved in the multi-million-dollar Joint Fire Science Project to develop science-based strategies for managing fire in western rangelands, including those dominated by invading juniper.

Juniper has waxed and waned over the past 6,000 years or more. Today, aided considerably by human activity, it is on the increase. It is not Miller’s place to say whether this is good or bad. “These questions come down to social values. But it’s important to manage the range ecosystem so it stays properly functioning. Whether you’re trying to grow pounds of beef, or enhance the habitat for sage grouse, or provide winter cover for large herbivores or tree cavities for desert birds, it’s important to maintain the health of the soil, functioning hydrological and nutrient cycles, and to keep a healthy understory in these communities.”

Published in: Ecosystems