The sagebrush steppe ecosystem in the West is remarkable. This area supports a range of wildlife, and in Oregon is home not only to the sage grouse, but also the mule deer. Trouble from invasive western juniper trees is pushing out native plants, though, and just cutting out these trees may not be the right tactic.

That’s what Oregon State University researchers found when they looked at areas overrun by juniper and non-native grasses. In a new study published recently in the journal Rangeland Ecology and Management, the OSU researchers found that simply cutting out the trees isn’t enough to restore the area. In fact, taking out these invasive trees makes it easier for non-native grasses like cheatgrass and medusahead to flourish.

Currently, there are major efforts to cut down western juniper as a popular way to stifle proliferation of the trees in the Northern Great Basin, which includes large parts of Oregon, Idaho and Utah, and nearly all of Nevada. Jacob Dittel, a postdoctoral researcher at OSU, noted that the concern is that instead of reducing competition to native shrubs and grasses with juniper by cutting, it may “be swapping competitors by increasing invasive grasses.”

He added that during the research, they found nearly twice as many juniper saplings underneath felled trees than in areas where there were no trees.

This research is important, because agencies are investing hundreds of millions of dollars in juniper reduction treatments to increase native shrubs and grasses. Much of the attention is focused on habitat recovery of some of the ecosystem’s notable inhabitants including the greater sage grouse, mule deer and many other native wildlife species found in the sagebrush steppe.

Western juniper is aggressive, forcing out sagebrush over tens of thousands of acres in the Northern Great Basin. The trees form dense stands that suck up rainwater and push sagebrush out. Invasive annual grasses are also a threat to the region, with plants including cheatgrass and medusahead pushing in to compromise habitat for key wildlife species. And those grasses provide fuel that could increase the frequency, and intensity, of wildfires.

Lisa Ellsworth, range ecologist, OSU Department of Fisheries and Wildlife and a study co-author, pointed out that the juniper reduction treatments are important from a wildlife habitat and range health perspective. But, she added, “When the understory is compromised, we need to consider follow-up treatments such as herbicide, and native shrub and bunchgrass seeding, to shift the balance towards native recovery."

The study is part of long-term OSU research in eastern Oregon, in cooperation with the Oregon Department of Fish and Wildlife, that considers the impact of juniper removal and postfire management practices on a sagebrush-steppe wildlife area.

Study details
The study was conducted from 2012 to 2016 near Flat Creek in the ODFW-owned Phillip W. Schneider Wildlife Area, between the Ochoco and Malheur national forests. In 2012, ODFW created six 2.4-acre blocks within the study site, with half of the block fenced to keep grazing cattle and feral horses out, and the rest open to grazing.

In the study, juniper was cut down with chain saws in late winter and early spring of 2013, and trees were left where they fell. In 2014, a large wildfire burned two of the three OSU sites. The study focuses on the unburned site.

The research team recorded effects of the juniper cutting on the plant community within the unburned site in 2014, 2015 and 2016. They saw an increase in native forbs and invasive grasses, and the invasive grasses were more predominant in areas where juniper was cut than in non-cut areas.

Added Dittel: “What we are seeing at this site is a general increase of invasive grasses in the understory, due to the juniper cuts. We didn’t see a strong response in perennial grasses or native grasses. We’re hoping that we’ll see a response further down the road."

Preliminary results on burned areas indicated that follow-up management, such as post-disturbance herbicide and seeding, can help suppress invasive grasses and enable edible forage plants to get re-established. They saw a large amount of juniper seedlings in the cut areas, which indicates that simply cutting down a juniper tree and leaving it where it lies probably won’t inhibit juniper expansion.

In another key finding, the researchers saw no difference in native or invasive plants between grazed and ungrazed treatments, so ODFW’s current low-intensity grazing regime is appropriate for the area.

The research team also included Ricardo Mata-Gonzalez, professor in the OSU Department of Animal and Rangeland Sciences; and Connor Morozumi, an OSU wildlife science graduate who is now a doctoral student at Emory University. ODFW funded the majority of the study, and the Oregon Beef Council partially funded Mata-Gonzalez’s participation in the study.

Source: Oregon State University