Tree removal could spread invasive grasses

This undated photo shows a slate of land choked out by western juniper.

ONTARIO — Removal of western juniper from rangelands is a common project for natural resource agencies and private landowners working to improve rangeland health and protect habitat for wildlife across the Northern Great Basin.

It is one of the tools being used to improve stands of sagebrush, which is critical habitat for the Greater Sage Grouse, once recommended for listing as an endangered species. The listing did not happen, but habitat improvement is still a major priority.

However, a recent study by a researcher at Oregon State University questions the effectiveness of some juniper removal and suggests that it could be contributing to the spread of non-native grass species, according to story written by Chris Branam, OSU Ag and Extension News.

“The concern is that instead of reducing competition to native shrubs and grasses with juniper by cutting it, we may be swapping competitors by increasing invasive grasses,” postdoctoral researcher Jacob Dittel was quoted as saying in the article. “Additional we found twice as many juniper saplings underneath felled trees than in areas where there were no trees.”

The spread of juniper has pushed sagebrush out of tens of thousands of acres of rangeland across the Northern Great Basin, the author said, as the trees have taken up water to the loss of sagebrush.

“Invasive annual grasses are also a threat to the Northern Great Basin ecosystem,” Branam wrote. “Plants such as cheatgrass and medusahead compromise habitat diversity for important wildlife species and provide fuel that could increase the frequency and intensity of wildfires.”

Lisa Ellsworth, a range ecologist and co-author of the study, said juniper reduction is important habitat protection and range health and additional steps are needed for adequate control of non-native species. Those steps can include use of herbicides and seeding of native shrubs and grasses, she said.

Dittel’s and Ellsworth’s study came out of a joint study between OSU and Oregon Department of Fish and Wildlife in an ODFW-owned wildlife area, between the Ochoco and Malheur national forests.

OSU researchers monitored juniper cutting on the site and the effects on the plant community from 2014 to 2016. Their findings were that invasive grasses were “more predominant in areas where juniper were cut than in non-cut areas.”

“What were are seeing at this site is a general increase of invasive grasses in the understory, due to the juniper cuts,” Dittel said. “We didn’t see a strong response in perennial grasses or native grasses.”

“The large amount of juniper seedlings in the cut-areas … indicate that simply cutting down a juniper tree and leaving it where it lays probably won’t inhibit juniper expansion,” Dittel said.

“Felling the tree stops the competition underground with the plans for water, but essentially they were dropping thousands of juniper seeds on the site,” Dittel added. “Those felled trees can act as a nurse plant which may facility juniper germination.”

After reviewing the OSU article, the staff at Malheur Soil and Water Conservation District, which writes grants to fund and sponsor juniper removal projects, emailed its response, agreeing with many of the study findings.

“Just cutting the juniper will not work as a sole treatment for restoration,” the staff wrote.

A larger project will be need to restore the landscape if invasive grases and juniper are both present, according to the response, and invasive grasses will increase when juniper is removed, SWCD staff said.

If juniper debris is not taken care of after a cut, microclimates for juniper seedlings will be created to help them, as well as other invasive plants, get established, the response states.

The Malheur SWCD officials agree that herbicides and seeding can help to suppress the invasive species and help forage plants to get established.

However, the staff commented that one study in one area does not represent all juniper treatments.

“Not all juniper cut projects are the same nor should they be treated the same,” the staff wrote. “A larger more long-term project with multiple sites, identical treatments that better follows ODFW’s more detailed restoration plan would show a better representation of what proper juniper cut project should look like.”

“A juniper cut project/treatment is more of a process than a one-time attack,” SWCD staff said. “A full-scale project takes proper planning, timing and proper treatment for what the actual project site needs.”

Another view expressed by people attending the Malheur Watershed Council meeting Thursday was that fire is one of the best controls for juniper if done right, as wildfires are also one of the top threats to rangeland health and sage grouse habitat.

Controlled burns, utilizing proper firebreaks were suggested as tools which could be successful, along with transplanting sagebrush to the cleared areas.

Getting approval such burns from neighbors and relevant agencies was seen a possible challenge.

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