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From wet to dry environments, eastern redcedar can grow in a wide range of weather conditions and soils. (Photo by Reagan Calk)

Managing The Menace

Thursday, May 26, 2022

Media Contact: Jami Mattox | Agricultural Communications Services | 405-744-8061 | jami.mattox@okstate.edu

If one asks landowners in Oklahoma if they are familiar with the eastern redcedar, a high probability exists they may show feelings of displeasure toward this encroaching woody plant species.

According to Oklahoma State University Extension, many Oklahoma landowners associate the eastern redcedar with groundwater loss, wildfire risk and pasture takeover. However, recent studies conducted by OSU faculty members suggest the eastern redcedar also may contribute additional displeasing side effects to areas inhabited by this plant.

“When I first came to Oklahoma State University as an assistant professor, I was looking for different ticks around the state,” said Bruce Noden, OSU Department of Entomology and Plant Pathology associate professor. “By doing this, I spoke to several landowners who informed me ticks can be found underneath eastern redcedars.”

After speaking with many Oklahoma landowners, Noden said he found it interesting no evidence of a relationship between eastern redcedars and ticks had been documented in research literature.

“One of the things we do as scientists is take this kind of information and figure out if it is true,” Noden said.

In the early years of research, the scientists found this invasive tree may allow expanded distribution of ticks throughout Oklahoma, Noden said.

Each eastern redcedar tree creates a microclimate better suited for supporting ticks and mosquitoes than the surrounding pasture, said Samuel Fuhlendorf, OSU Department of Natural Resource Ecology and Management Regents professor.

“Eastern redcedars largely influence humidity, wind and temperature,” Fuhlendorf said. “The wind inside the canopy of the redcedars becomes calmer and holds more water, making it warmer or cooler, depending on the time of year.”

Noden said ticks use eastern redcedar trees because they provide a habitat for the arthropods to expand where they could not before.

The humidity is high enough underneath an eastern redcedar’s canopy for ticks to survive without an animal host in dry places like western Oklahoma, Noden added.

“After the ticks take a blood meal from animals, like deer, they drop off the hosts, and they die unless they are near something that fits their preferred abiotic conditions, like a cedar tree,” said Scott Loss, OSU NREM associate professor. “The area under the tree often will retain enough moisture even if it is drier in the open.”

The native range of the eastern redcedar tree is eastern Oklahoma and regions further east, Loss said. The plant is usually confined to places that escape fire like rocky ravines and outcroppings, he added.

“Dr. Noden and I have been studying tick-borne diseases for almost nine years,” Loss said. “We recently received a National Institutes of Health grant for the next two years to study how different stages of eastern redcedar encroachment affect tick populations and tick-borne diseases.”

The NIH grant does not include research on how eastern redcedar trees affect mosquito populations and the transmission of diseases like West Nile virus, but the researchers hope to receive funding for that topic in the future, Noden said.

“West Nile virus is transmitted from birds to mosquitoes and from mosquitoes to birds,” Noden said. “We see peaks of West Nile virus in August, September and October when mosquitoes start to feed on humans, horses and donkeys, instead of birds.”

In the winter, the birds migrate south, and the mosquitoes die, but West Nile virus stays, Noden said.

A small number of mosquitoes can transfer the virus to their eggs, so when the offspring hatch in the spring, some may be infected, he added.

The American robin is considered a “super spreader” for West Nile virus in other regions and prefers eastern redcedars because they like feeding on the cones the tree produces, Loss said.

“We have found the mosquitoes that transmit viruses in other places, such as Zika virus and Western equine encephalitis virus, prefer to live in redcedars,” Noden said. “An outbreak of these diseases are not happening now, but it is a risk.”

Disease distribution is altered by things that change the distribution of the invertebrates and wildlife that transmit diseases, Loss said.

Those distribution disruptions can include climate change, people’s commerce and the transfer of goods, he added.

“Oklahoma already has the mosquito vectors we know are physiologically capable of transmitting the pathogens that cause disease,” Loss said. “This tells us if these diseases do move in, the eastern redcedar could help facilitate their transmission.”

The new NIH grant is one of the first comprehensive, fully funded studies looking at the worldwide issue of how woody plant encroachment affects disease, especially with eastern redcedar, Loss added.

“The Prairie Project recognized the greatest threat to natural resources in the area is the encroachment of woody plants, most of which is eastern redcedar,” Fuhlendorf said. “The research project Dr. Noden and Dr. Loss are doing will give us a new, and possibly the biggest, talking point in terms of why this is a serious issue.”

In Oklahoma, people must be aware of the risks of having more ticks and mosquitoes in an area, Noden said.

The ability to link issues back to a specific place on their property will allow landowners to identify a specific source of health risks to humans and animals in the future, he added.

“There has been a big push to conduct research that supports the removal of eastern redcedars,” Loss said. “If we find this plant is facilitating many infectious diseases further west than they used to be, that will provide another compelling piece of information to help people decide how they need to manage eastern redcedar.”

This research may allow the faculty members to measure how different levels of eastern redcedars encroachment affect tick populations and disease prevalence so people can avoid allowing the plant to grow beyond a certain point, Loss added.

The research results will be useful for rural people who own land as well as attract the attention of urban people, Fuhlendorf said.

“If we could better understand how what is on the land affects the prevalence of pathogens in ticks and mosquitoes, then we could better predict where on the land is to be more problematic from the perspective of human, wildlife and domestic animal disease," Loss said.

“Eventually, we could help direct public health efforts benefiting human health or veterinary health."


Story By: Reagan Calk | Cowboy Journal

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