An Illinois River Hill Prairie Fire

For prairies to persist in Illinois, with a climate that has long favored wooded habitats over grassland, periodic fire is a requirement. Later in the spring, a burned-off prairie will revive from its extensive underground root system, and prairie wildflowers and grasses may gain a competitive advantage over always encroaching shrubs and trees.

Of Illinois’ few remaining original prairies, hill prairies are some of the best examples. They occur on southwestern-facing bluff tops bordering river valleys, places that are too steep or rugged for farming. This photo essay shows the burning of a small glacial drift hill prairie at Crevecoeur Nature Preserve (Fort Crevecoeur Park) in Tazewell County, Illinois, on March 30, 2010.

 

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At 11:15 AM, relative humidity was 41%, air temperature 56 ^oF, and wind was blowing 8 to 10 miles per hour from the south-southeast – in Photo 1, essentially from left to right, directly across the hill prairie ridge. The Illinois River is visible through the trees on the right-hand side of the photograph.

Photo 1.

 

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To avoid a wild fire, controlled burns usually begin by lighting a back fire (Photo 2), which moves slowly against the wind. Later, a head fire (i.e., with the wind) will be lit, and the two will meet and burn each other out.

Photo 2.

 

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In Photo 3, the back fire is being lit just inside of the tree line, beyond and around the base of the ridge. At this point, the back fire will turn into the head fire (Photo 4). Meanwhile, the back fire has been gradually moving up the slope, creating a wider burned off area that will prevent the head fire from further advancing. Note in Photo 5 the blackened area visible in the foreground, a result of the back fire reaching this point on the ridge top.

Photo 3.

Photo 4.

Photo 5.

 

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Flames, burning debris, and ash from the head fire are being whipped across the ridge by brisk winds (Photo 6). In seconds, the back and head fires will meet. The main fire is out (Photo 7 and Photo 8), and only smoke is being swiftly carried across the ridge. Blackened ground and smoldering embers of woody debris and bunch grasses are all that remain. But before too much time passes, green shoots of prairie plants will begin emerging from the black; without the previous year’s interfering thatch, the growing plants will receive greater amounts of sunlight than in years without fire.

 
Photo 6.

Photo 7.

Photo 8.

 

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The Context of Burning. There are seemingly hundreds of details, large and small, to keep track of when planning a safe, controlled fire: writing a detailed burn plan, constructing fire breaks and other labor-intensive site preparations, notification of neighbors and local fire departments, checking and repairing equipment, obtaining weather forecasts, and assembling a crew (one does not burn alone), to name only a few. Still, the evening before the scheduled burn, uncertainty about the weather remains. How accurate is the forecast? Could it change at the last minute? Will it be too wet, too dry, too humid, too hot, not hot enough, too windy, wind from the wrong direction? Should the burn crew be notified to assemble the next day as planned or should the burn be called off?

The responsibilities weigh heavily upon the burn leader; anxiety levels run high. The night before a burn, dreams are filled with visions of fire, sleep is fitful, the mind races.

After the burn crew has been mobilized and de-briefed and equipment is in place, the back fire may be lit; later, the head fire. Sometimes the flames of the head fire quickly rise to a roar, like an uncaged lion, and go charging off. The cat is out of the bag. Pandora’s Box has been opened. But if the burn has been well planned, and that better be the case, there is nothing to fear: the fire will burn out of its own accord as planned.

It is only then, after the fire is out, that there is time enough to recall the context in which we are burning: unleashing a force upon the land in a similar way, though on a smaller scale, as Native Americans had done for thousands of years. Were it not for their burning, it is unlikely that prairies would have survived in Illinois, from encroachments of forests, to greet the first European explorers. But when the Europeans finally did arrive, they saw an untrammeled Illinois wilderness; though to the Native Americans, that same scene was home and a landscape highly influenced by their activities.

Such thoughts might be briefly reflected upon immediately after a burn, but there is still much more work to be done; though one may be weary from smoke and stress, control lines must be checked again to ensure that the fire is truly out and everything is secure. If that is the case, fire control equipment will then be gathered and the burn crew released.

Returning to the burn scene the following day is a good idea, to walk the fire breaks again and more closely inspect the burn results, checking whether or not the fire had lived up to expectations. Did it help set back woody encroachment? Was it a complete burn or a mosaic of burned and unburned areas? Will another burn be required next year or should it wait a few years. Lack of evaluation would be almost as bad as not burning at all. Once begun, the work never ends.

[NOTE:  This article has been published in the Fall 2010 issue of Illinois Audubon magazine, pages 17-19.  See www.illinoisaudubon.com.] 

Comments

[Julie]

Very interesting!