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To experiment with different burning frequencies, John Blair said Konza is divided into watersheds based on the topography of the land. Some watersheds burn annually, every two years, four years, 10 years or 20 years.


Periodic fires important

"How do you maintain a grassland? Burn it."

By April M. Blackmon



Landscape view of Konza Prairie
Photo by April M. Blackmon.

Prairie fires have rolled through the American plains throughout history, destroying woody vegetation and preserving native grasslands. John Blair, a Kansas State University associate professor of biology, has spent time at Konza Prairie Biological Station looking at fire and the factors important in maintaining what's left of America's native tallgrass prairie.

An ecosystem ecologist, Blair and other researchers have been studying how fire affects the tallgrass prairies. Blair's research focuses on nutrient-cycling changes caused by fire in these grasslands and how plants respond to those changes.

"When you burn a prairie, the nitrogen that's in the litter and above-ground biomass literally goes up in smoke," he said. "Nitrogen is one of the key nutrients that can limit the grassland's productivity. Burning decreases nitrogen availability and that tends to favor the warm season grasses, which are dominant plant species in these grasslands."

Nitrogen is important in determining nutritional quality for organisms feeding on the grasses, whether it's grasshoppers or cattle, Blair said. The nitrogen content of dead grass, or detritus, also affects decomposition rates, which affects the storage of carbon in the soil over time as well.

"Anything that changes the cycling of nitrogen in these grasslands will affect food quality, storage of organic matter, productivity and potentially the diversity of these grasslands, too, because plants compete for nitrogen," he said. "So if you change nitrogen availability, you might change the groups of plants that occur there."

Periodic fires were essential in keeping woody vegetation from growing in the area and maintaining the dominance of native grasses in the ecosystem, Blair said. Experimenting with different fire patterns at Konza, researchers are looking at the various effects of different fire frequencies.

"Ideally, a land manager might want to mimic the natural pattern of historic fire frequency, but we don't know what that was," Blair said.

"In some places, like forests, you can look at things like fire scars and tree rings to get an idea of how frequently the forest used to burn. But with grasslands, there's virtually nothing to leave a record like that."

Studying different fire frequencies is important, because they have various effects on the land, Blair said. Burning more often decreases plant diversity, tending to favor the warm-season grasses that ranchers and land managers like, while burning less often causes an increase in the growth of shrubs and trees, which could eventually mean the conversion of grassland to forest, he said.

"In the Flint Hills today, around areas where there's been human development, the amount of land covered with shrubs or with cedar trees has increased. Historical photographs of this region show that most of the vegetation in the Flint Hills was grass — it looked like Konza," he said. "The increase in woody plants today is probably due to a change in fire frequencies."

Researchers look at what the different fire frequencies do in terms of plant responses like productivity and species diversity, as well as changes in soil properties, animal communities, etc.

In addition to the effects of fire frequencies, researchers are also looking at how burning during different times of the year affects the ecosystem.

"Most of the burning today takes place in the spring, because that's the best time to control woody growth and favor the grasses," he said. "But because historically, fires could occur any time of the year here, depending on when lightning would strike or when Native Americans would light fires, we've just started to ask the question: 'How does the prairie respond to burning at different times of the year?'"

June 2002