Thursday, November 19, 2009

Fall burn promotes health of woodland at Allerton

Fall burn promotes health of woodland at Allerton

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Last Friday morning I was among a small group of people who came together in a parking lot at Robert Allerton Park near Monticello and prepared to set the woods on fire. Of course this wasn’t a group of thrill-seeking teenagers bent on destruction. Among those gathered were scientists and managers from the University of Illinois and the Illinois Department of Natural Resources, a field representative of the Illinois Nature Preserves Commission, and the acting natural areas manager of the park. Our purpose was to conduct a prescribed burn to promote the ecological integrity of the oak-hickory forest at the site.

How does fire promote ecological integrity in an oak-hickory forest? Partly by knocking back invasive exotic plants that would otherwise crowd out native understory flowers and shrubs. In addition, burning has the effect of killing off native maple trees, which is also a good thing. In the absence of fire, maples will eventually replace oaks and hickories through a process of succession. This process was regularly interrupted prior to European settlement in Illinois by burns that Native Americans conducted.

A rotation of prescribed burns is now part of the overall design to manage the natural areas at Allerton, where the aim is to restore the native diversity of plants and animals by controlling invasives such as garlic mustard, multiflora rose, and privet.

As you might imagine, there’s a certain pleasure in lighting a big fire and watching it sweep through the woods. But that’s really only the culminating step of a prescribed burn, a step made possible by a great deal of preparatory work.

Our burn was conducted according to a plan developed by IDNR Heritage Biologist Eric Smith. That plan was drafted a year ago and approved by supervisors at DNR as well as the Illinois Environmental Protection Agency. It specified the boundaries of the burn unit, the number of people who would be involved, the weather conditions that would be acceptable for burning, what fire containment equipment would be on hand, and more.

Prior to the burn we cleared leaves and other flammable debris from the wide trails that served as firebreaks, and all members of the burn team reviewed the plan for the day together.

Here’s how it worked. The outline of our burn was a U-shape, with the Sangamon River corridor forming the open end on the north, and the wind blowing toward that end from the south. Shortly before noon we split into two groups, each of which began lighting fire at one tip on the U and continued down along the side, converging at the closed end. By design, the fire moved into the burn unit slowly from the sides of our U, and more rapidly from the closed end, since the wind pushed it along from that direction.

Our woodland burn at Allerton was never as dramatic as a prairie fire, since it was fueled only by fallen leaves and the small amount of down wood that was dry enough to burn. But now and then a standing dead tree or a broken limb with dried leaves still attached would ignite and send flames roaring skyward.

By 4:30 in the afternoon all remaining fire was contained in the blackened area, and most of the burn crew was able to leave, save for Allerton’s natural areas manager Drew Becker, who remained into the night to monitor material that was still smoldering.

Mary Kay Solecki of the Illinois Nature Preserves Commission, who stepped in as “burn boss” when Eric Smith injured his knee prior to the burn, termed it a success: “Everything we wanted to burn burned, and nothing burned that we didn’t want to burn. And the fire was hot enough to kill the plants we wanted to kill.”

Visitors to the woods near the Lost Garden at Allerton Park should be able to witness this success for themselves. Next spring the green of emerging wildflowers will stand out in contrast to the blackened ground. In the long term, the understory will remain open and favor the regeneration of the oaks and hickories in the forest.