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Ecology of Fire in Semi-arid Grasslands of Colorado

David J. Augustine & Justin D. Derner

Rangeland Resources and Systems Research Unit, USDA-ARS, Fort Collins, CO

Daniel G. Milchunas

Colorado State University, Fort Collins, CO

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Rangeland

Analysis

Platform:

Northeast

Colorado

Boulder

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Fire in Shortgrass Steppe

Historically a component of the shortgrass steppe, although return intervals are uncertain. Wright and Bailey (1982, Pg 80-81) noted:

“In the semiarid areas, big prairie fires in the past usually occurred during drought years that followed one to three years of above average precipitation, because of the abundant and continuous fuel.”

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Fire in Shortgrass Steppe

Historically a component of the shortgrass steppe, although return intervals are uncertain. Wright and Bailey (1982, Pg 80-81) noted:

“In the semiarid areas, big prairie fires in the past usually occurred during drought years that followed one to three years of above average precipitation, because of the abundant and continuous fuel.”

Fire in 1885 started near the Arkansas River, western KS: “It jumped the Cimarron River, burned across the North Plains of Texas, and did not stop until it reached the rugged Canadian River Breaks, a distance of 175 miles. About 1 million acres of the XIT Ranch alone burned in Texas.”�
Fire in 1974 started in Lea County, NM: “The fire travelled 26 miles, burning 52 sections, and crossed three major highways. It was stopped by a plowed field”

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Predicting Fire Frequency with Chemistry and Climate

~10-14 yr fire return interval

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Traditional Fire Management

Tallgrass Prairie:

Burns enhance forage quality; whole pastures burned to encourage uniform utilization by livestock

Well-developed culture of fire management

Shortgrass Steppe:

Fires widely suppressed

High fuel loads occur infrequently

Lack of fire management culture

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Fire Behavior and Fuel Loads in Shortgrass

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When Does Shortgrass Burn?

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When Does Shortgrass Burn?

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When Does Shortgrass Burn?

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Fuel Load vs. Head Duration and Dosage

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Effects of Wind Speed on Fire Intensity

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When Does Shortgrass Burn?

Fuel Load > 350 kg/ha

Relative Humidity 10 - 20%

Air temp >60˚F

Winds 7 – 15 mph

Mean Peak Fire Temps: 100 – 150 C

Fuel Load > 700 kg/ha

Relative Humidity 10 - 25%

Air temp >60˚F

Winds 7 – 15 mph

Mean Peak Fire Temps: 150 – 190 C

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Ecological Effects of Prescribed Fire

in Semi-arid Grasslands

Plant Community Composition

Vegetation Productivity

Wildlife Habitat

Interactions with Grazing

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Prescribed Fire & Cactus in Shortgrass Steppe

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Prescribed Fire & Cactus in Shortgrass Steppe

Late Winter Burns (March):

Study #1:

Reduced cladode density by 35% (range 23 – 58%) in first post-burn growing season.

Study #2:

Reduced cladode density 22% in first post-burn growing season

Fall Burns (Oct - Nov):

Reduced cladode density 66% (range 50 – 82%) in first post-burn growing season.

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Fall Patch Burns: Effects on Cactus

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Prescribed burning and Six-Weeks Fescue

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Dormant-season Prescribed Burn Applied when Six-weeks Fescue Has Recently Germinated (Oct-Nov or March)

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Dormant-season Prescribed Burns also have potential to suppress invasive annual bromes (cheatgrass)

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Prescribed Burning for Wildlife

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Prairie Dog Colonies As Effective Fuel Breaks

Satellite-based Map of Grass Biomass in Northeast CO

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Fire-Grazing Interactions in Shortgrass

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Patch Burns Alter Cattle Grazing Distribution in Shortgrass

Late May/Early June

2 steers in herd of 24

2 steers in herd of 240

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Ecological Effects of Prescribed Fire

in Semi-arid Grasslands

Plant Community Composition

Winter-germinating annual grasses
Cactus

Vegetation Productivity

Little to no detectable effect

Wildlife Habitat

Prairie dog colony expansion
Mountain plover nesting habitat

Interactions with Grazing

Post-burn attraction of grazers, even in low-biomass grasslands
Prairie dog colonies create fuel breaks

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Fuel Loads in Front Range Grasslands?

RAP

Grass-Cast

Forecasted Production

Future

Present

Condition Monitoring

Past

Historical Production

Grass-Cast is one of the few tools that peers into the future to try to make an educated estimate of how many pounds per acre might grow, in total over the growing season, depending on how precipitation and temperatures unfold during the season. Instead of giving a snapshot of current rangeland conditions, it looks out to the end of the growing season and estimates how far above, near, or below-average we expect grassland production to be relative to a local area’s long-term average.

For areas not served by Grass-Cast (because of a lack of long-term clippings datasets), there are some other tools you can check out (they depend more heavily on satellite-sensed data, and not on-the-ground clippings datasets), such as FuelCast.

And for real-time monitoring, as well as historical production estimates, there are tools like RAP and Land PKS. The next few slides show where you can find these other, complementary tools.

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Estimating Grassland Productivity with

the Rangeland Analysis Platform

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Forecasting Grass Growth in the Current Year

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Forecasting Grass Growth in the Current Year

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Forecasting Grass Growth in the Current Year

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Whats the Probability of High vs. Low Precipitation in the Next 3 Months?

Questions?

David.Augustine@usda.gov

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