The unique ecosystem of the Kansas prairies has relied for centuries on fire and large, grazing ruminant animals.
Long before white settlers arrived, the Native Americans set the prairie afire in the springtime — not because they understood the symbiotic relationship of the grasses and forbs to the subsoil microbiology that nourishes them, but because it brought a flush of rich, new green grasses, which in turn brought the bison.
The white settlers who followed them continued the practice of burning to renew the prairie and turned their cattle into the pastures when the new flush of green arrived. They understood that fire cleansed the prairie of woody shrubs and weeds that threatened the desirable grasses. They traditionally burned in the spring, because renewed grass in that season provided the nutrition their herds needed after a long winter.
Over time, however, some new concerns arose, especially as the population of the region grew. Spring weather in Kansas can be challenging, and the days with winds and humidity favorable for burning can mean that hundreds of acres are burned in a short window of time — and the resulting smoke can create air quality problems for towns and cities.
Another concern noted by ranchers and range managers was that spring burning, while very effective against eastern red cedars and other woody plants, was not providing good control of an invader that was growing increasingly worrisome: sericea lespedeza.
Looking for answers
That led Kansas State University range cattle scientist K.C. Olson and a team of researchers to question whether or not there might be a better time to apply fire in pastures where sericea was threatening to take over the ecosystem.
“What if we burned at the time of year when the plant might be the most vulnerable to fire, at the point of flowering or the beginning of seed set?” Olson recounts. “That would be late summer, in August or early September. Would that give us better control? Would it have a negative impact on the performance of yearling stocker cattle?”
Olson and his team decided that research was the way to get answers, and they conducted limited studies of nine 14-acre plots between 2014 and 2017 in Geary County. The average date the plots were burned was on April 1, Aug. 1 and Sept. 1.
By 2016, Olson says he could see that the late-summer and early-fall burns were have a strong effect.
“Before we were done, we knew we had a pretty exciting solution and a pretty exciting talking point for the people of the Flint Hills,” Olson says. “Those first results ended with less than 2% sericea lespedeza basal cover on the two alternative fire treatments, and more than 11% basal cover on the spring-burn plot.”
A subsequent study also measured the variance in gain performance of yearling stockers following burns in mid-April, mid-August or early October. They found no difference at all between spring and summer burns, and a little less than a 20-pound weight drop with fall burning.
“If I had to give an edge to one treatment, it would be summer,” Olson says. “We saw strong performance by warm-season tall grasses, no upsurge in annual weeds, but a gain in native legumes and nectar-producing plants in the summer treatment. That’s a very good thing. I couldn’t be more excited about the results,” Olson says.
Waubaunsee County rancher Joe Carpenter said he has had good luck with knocking back sericea with a late-summer burn, especially on level land.
“It worked great on the flat ground, but didn’t have enough heat when creeping down the steep draws. The fire was easy to control, but with all the green, there was a lot more smoke. It does seem to be catching on, and we are planning to do some patch burning eventually,” Carpenter says.
What happens next?
Olson says his team will continue their current studies for some years to come. These will explore whether late-summer or early-fall burns can effectively control other invasive species that have become concerning: Old-World bluestems, namely yellow bluestem and Caucasian bluestem.
“They’re another thing we did to ourselves,” he says. “They were brought into the state as either hay or seed. They were cultivated, and in many cases, have since displaced the native vegetation,” he says.
K-State studies as well as data out of Texas indicate the seasonal burning thwarted the growth of yellow bluestem, he says.
Olson said he has conducted a study of the impact of off-season fire as a control for the invasive Old-World bluestems on a site in Ellsworth that has a significant infestation of Caucasian bluestem.
Off-season burning brought a 38% decline in basal frequency, with significant replacement by native grasses and forbs.
Olson says Old-World bluestems are not technically related to native bluestem grasses, but they have invasive characteristics and a negative impact on the native grasses.
“It’s just coming up on the scene, and we don’t have a good handle on how many acres are infested. We do know that sericea is a problem on about 950 square miles statewide, with the majority of that in the Flint Hills,” he says.
Off-season burning in late summer or early fall also has advantages for smoke management, Olson says.
“There are two key differences for smoke,” Olson says. “In the spring, days are typically warm but nights are much cooler. During the day, the smoke plume rises and dissipates high in the atmosphere. But when the air cools at night, the smoke sinks to ground level, and that can cause air-quality problems. In the summer, the nights stay warm enough that the smoke plume stays airborne.”
The second advantage is that in the summer, when the grasses are typically green, combustion is incomplete, and a lot of dead plant material is left standing on the surface.
“It doesn’t become gas or small particulate matter,” he says. “That helps air quality, too.”
Olson says he is not suggesting that all burning be moved to summer or early fall. “For some ranchers, the spring burn gets the job done for controlling woody-plant problems and keeping their pastures clean. There is no reason for making a change. For others, that’s not the case, and it is exciting to see them have an alternative.”
Knowing that off-season burning is effective also provides an option for range managers who missed the weather window for a spring burn.
“There are seasons when a rancher really wants and needs to burn for weed control, and to eliminate the fuel buildup that can contribute to wildfire danger, but the weather just refuses to cooperate. Those people now know that burning in August, after the intensive stocker grazing season is over, can help them be in a better place for the coming season,” Olson says.
The dollars and cents of it
Olson said in the years since his first results were announced, more ranchers are opting to burn later, and smoke plumes in the Flint Hills are increasingly seen from mid-August through September.
Ranchers are eager to have options for sericea control and excited about the performance data for cattle, which shows that late-summer and early-fall burning provide effective control at a much lower cost than treating those infested acres with herbicides.
Treating 3 acres of pasture — the typical grazing footprint of a stocker animal — with fire costs about $2.25. A herbicide application on the same footprint is about $54.
Olson’s team determined that this means a rancher could give up 70 pounds of total weight gain and still break even using fire instead of herbicide.
The study found that performance data showed much less impact. Gains were roughly equivalent on rangeland burned in the spring and rangeland burned in late summer, while cattle that grazed the fall-burned pastures were about 20 pounds behind, far below the 70-pound breakeven level.
“Summer burns typically take a lot fewer people and a lot less equipment than a spring fire does,” Olson says. “The amount of standing green material with moisture slows the speed of the fire, and wind levels that can be tolerated are higher than in the spring. The chances of a fire getting out of control are significantly less.”
Best of all, Olson says, the opportunity to vary burning times means the Flint Hills are becoming healthier, and the team is excited to see prescribed fire practices being reintroduced to rangelands across the Great Plains.
“Every year, we’re giving up more land to woody invaders and catastrophic wildfires. We have only begun to tap the potential for prescribed fire for ecosystem management and improvement,” Olson says. “It is my hope that we can keep an open mind and not get into a rut of doing things the same way all the time. Using fire during most of August and early September is low-cost and low-risk, and helps us be a better neighbor with respect to smoke management. It’s an excellent way to take back those invaded acres and build carrying capacity on our rangeland.”