A tree imported from Asia roughly a century ago has invaded many riparian areas, earning it the Wyoming status of a noxious weed in 2006. Recently in Park County, a coalition of entities launched a campaign to reduce Russian olive groves along the Shoshone River, to benefit local vegetation, wildlife and people.
Preferring riverside and disturbed areas, the tree “eventually crowds out native species,” explained Jarren Kuipers in a talk at the Buffalo Bill Center of the West. “Russian olives don’t play well with others. They crowd out native vegetation and reduce productivity in the riparian corridor.”
A wildlife biologist with Land Steward Services, he participated in a four-year study to determine the effects on little animals of eradicating the noxious weed and shared the results in the Nov. 7 program.
“The removal of Russian olives had a pretty profound impact on small mammals,” Kuipers said.
This fall there was another study on the trees’ removal, focusing on the impact on birds, with the analysis due next spring, said Abby Scott, northwest Wyoming program director for The Nature Conservancy, in an interview after the BBCW program. TNC leads the Shoshone Revegetation Project, which she said was “spurred by the Russian olive infestation becoming a growing concern among landowners and agencies.
“It’s proliferated to nearly every river and riparian area.”
Russian olives are “extremely adapt reproducers,” Scott explained. They drop seeds into the water that colonize downstream areas, they send up suckers and their seeds are spread by wildlife.
“They can take over wetlands, lowlands and irrigation ditches,” she said. “They can wreak havoc on any place with water.” Further, “they tolerate drought and a wide range of soil types.”
While the fruit is edible, it offers little quality as forage, Scott added.
“The real problem is Russian olives come in and take over,” she said.
They outcompete native vegetation, shade the ground so little grows there and create dense thickets impenetrable to livestock, humans and wildlife, including tiny critters.
“Small mammals respond quickly to habitat change,” Kuipers said. They’re a good study subject because they offer a variety of species, have small ranges of 1-2 acres and sit at the bottom of the food chain. “A slew of predators depend upon them.
“Voles are semi-aquatic so they’re vulnerable to fish,” like trout, he added. Other predators include Great Blue Herons and snakes.
The mammals’ riverside habitat typically includes narrowleaf cottonwoods, willows, buffalo berry, wild licorice and other forbs important to pollinators, Kuipers said. They’re lost when Russian olives take over, shrinking the diversity of vegetation for small animals.
The deer mouse, western harvest mouse, meadow vole and long-tail vole comprised his subjects. Using 400 live traps, Kuipers found that more mammals inhabited the riparian areas after they were cleared of Russian olives.
“It was a catch and release study,” Kuipers noted.
His study sites comprised two control areas and two treated areas.
The TNC-led project involved treating about 400 acres from Cody downriver to Byron, Scott said. Teams using heavy equipment removed trees bigger than five inches in diameter and chemically treated the stumps and smaller trees, starting in 2014. Subsequent treatment continued for the next three years.
“It was a pretty ambitious project. It was quite an undertaking,” noted Scott, who estimated the total cost at about $500,000. “It was a very hefty price tag.”
Follow-up, along with the bird study, will mean evaluating the removal sites to see if replanting is necessary.
“So far, many places have revegetated naturally,” she said. “Native plants are incredibly hardy. The Nature Conservancy is most interested in native plants and diversity.”
Early treatment of Russian olives is less expensive and less difficult than attacking them after they’ve infested an area.
“It’s ideal to not let it get to that point,” Scott said. Ideally, she said, landowners and agencies will take the lead in controlling the noxious weed, a campaign that promises a rich reward.
Eliminating the Russian olives will create “a healthy riparian system and a useable resource for people,” Scott said. “We want the river to thrive and continue to be an important resource.”