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Invasive plants influence fire and outcompete natives in burn scars

by Wyoming Livestock Roundup

Douglas – “We are starting to see fires earlier in the season and seeing them burn longer,” Chris Weydeveld, Firewise coordinator for Washakie and Big Horn Counties, said at the North Platte Russian Olive Control Workshop held July 30 in Douglas. “We are also seeing a lot more vulnerability in homes and in wildlife habitat near river systems.” 

In his presentation, Weydeveld examined Russian olive and salt cedar presence as a threat to riparian area vegetation and as a damaging fuel in forest fires.

Planting invasive species

“Russian olives were brought into the United States during the 1900s,” explained Weydeveld. “Salt cedar could be found in horticultural catalogs as early as the 1820s. They were sold in nurseries in California around 1856 and were used extensively as windbreaks and for stream bank stabilization.” 

The popularity of these plants has increased their prevalence in the western states. Weydeveld said that a study conducted in 2005 found that, out of 42 species that were found along rivers, salt cedar and Russian olive ranked as the third and fourth most common species.

“Russian olive and salt cedar have not reached their maximum potential range,” he continued. “They have the ability to expand into more areas. With changing global temperatures, these invasive species are expanding farther north and into higher elevations.”

Both plants are highly invasive species that displace vegetation and compete heavily for resources.

Influence on fire

“It is becoming the norm to see nine or 10 million acres burned in wildfires each year,” Weydeveld elaborated. “Fires are getting harder to fight. We are seeing heavier fuels building up and, at the same time, budgets are getting cut, so there are not as many firefighters battling the fires.”

“Historically, especially in Ponderosa pine forests, fire would come through every five to 25 years, burning the undergrowth and leaving the mature trees unscathed,” he explained. “Fires were an integral part of the ecosystem. When fires were removed from the ecosystem, it removed a healthy aspect. Now, shrubs and invasive species are dominating the undergrowth and act as ladder fuels during fires, burning trees that would have otherwise survived.”

“Fuels are the source of energy that drives the fire,” he continued. “Fire behavior depends on certain fuel characteristics which include fuel type, fuel availability and arrangement.”

“Surface fuels are the fine, flashy fuels that carry the fire,” the Firewise coordinator added. “Ladder fuels are how the fire transfers from the surface to  aerial fuels.”

“Aerial fuels are those in the canopy or crown of the tree,” he explained. “A fire will generally not burn into the crown of a tree unless there are ladder fuels underneath.”

During his presentation, Weydeveld showed images of regrowth from a recent fire in Wyoming. After the blaze, salt cedar and Russian olive trees began regrowing after only a few months. It was not long before they dominated the area while the native species struggled to grow. 

“There have been reports that cottonwoods flourish after a fire, but I did not see that following the 2008 Dike Fire along the Bighorn River in Greybull,” he explained. “Russian olive and salt cedar, however, flourished.”

Removal of invasive species

Weydeveld suggests the removal of the invasive species to improve vegetative health and decrease the risk as a fire hazard. Burning the plant will only aid regrowth, so landowners must look to chemical means to remove them. 

An effective method for removal is cutting the tree down and then applying a diluted broadleaf herbicide to the stump within 15 minutes of cutting the tree down.

“A combination that has worked well is one part Element, or triclopyr, to three parts basal bark oil,” Weydeveld said. “If applied within the 15 minute window to a debris-free stump, there is an 80 percent efficacy. Herbicides containing glyphosate, such as Roundup, will also work.”

“For the 20 percent that do sprout from the root crown, it is important that landowners go back the following fall and apply a foliar spray on the returning sprouts,” he added.

Weydeveld also cited September to early October as the best time to remove the trees. 

“September is the ideal time because that is when the plants takes much of the energy from the leaves and branches and pulls it down into the roots,” he explained. “When the herbicide is applied during that time, it is pulling it down into the roots as well.”

“This is also an ideal time because it is cooler than earlier in the summer. Hot temperatures can cause the herbicide to volatilize and evaporate into the air,” he elaborated. “This can cause damage to aerial portions of desirable vegetation.”

The herbicides can be obtained from Weed and Pest offices across the state. 

“Every county in Wyoming has a Firewise coordinator that will come to a property and conduct a fire fuels hazard analysis free of charge,” said Weydeveld. “They will also give recommendations on how to make the area more defendable in case of a fire.”

The Russian Olive Workshop was sponsored by Pathways to Water Quality, Wyoming Game and Fish Department, Wyoming State Forestry, Dow Agrosciences and Upper North Platte River Weed Management Area. Kelsey Tramp is the assistant editor of the Wyoming Livestock Roundup and can be reached at 

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