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Prescribed Burns Enrich Soil, Help Control Invasive Plants

A man monitors a fire in a prairie setting.
Prescribed burns are carefully planned to provide ecosystems with the benefits of the natural process of fire.
February 28, 2017

Visitors to The Morton Arboretum in the springtime sometimes come across a patch of blackened earth and burned plants, with a whiff of recent smoke. Is this the aftermath of some disaster? Hardly. It’s a sign of smart work to improve the Arboretum’s ecosystems.

The black patches are places where trained Arboretum staff and stewards have conducted prescribed burns: They have deliberately set fires to burn away the dead stalks and leaves of last year’s plants. Why? Because science has shown that native plant communities need fire, according to Kurt Dreisilker, head of natural resources.

“Our local ecosystems evolved with fire,” Dreisilker says. The fire enriches the soil, helps control invasive plants that compete with native plants, and encourages a wider variety of species to grow.

Before European settlement, lightning or Native Americans would set fire to most patches of prairie every few years; woodlands would burn less often. Bur oaks, which grew widely scattered amid prairie plants, are an example of plants that evolved to tolerate fire. A bur oak has thick, corky bark that insulates the trunk to reduce damage from a fire. Meanwhile, the fire removes competing tree saplings before they can grow to compete with the oak for sun.

Today, prescribed burns, also called controlled burns, are carefully planned to provide ecosystems with the benefits of this natural process while keeping people and property safe. The technicians who do the work are extensively trained and carefully equipped. The Arboretum obtains all the required permits. Visitors are excluded from areas to be burned for their safety. The weather must be perfect, dry with little wind to fan flames; if conditions aren't just right, the burn is postponed.

“Safety is always paramount,” Dreisilker says.

Only a selected area is burned at a time. One technician uses a special torch to set fire to the dried vegetation in front of him. Others use sprays of water to corral the fire and extinguish it as soon as its work is done.

Most prescribed burns are done in early spring, while dead stalks and leaves are still on the ground, although some are done in autumn after the leaves fall, according to Dreisilker. Burns can’t take place when conditions are wet because of spring rains or winter snow.

Prescribed burning began in The Morton Arboretum’s Schulenberg Prairie in the 1960s and has been a regular practice in all its natural areas, including woodlands, since the 1980s. Decades of research, at the Arboretum and elsewhere, have conclusively demonstrated how important fire is to native ecosystems and have improved our understanding of its benefits.

Only one patch of the Arboretum’s natural areas is never burned, Dreisilker says: It’s kept as a control for research on the effects of burning, so researchers have something to compare their results to. When you drive along the Main Route just east of Parking Lot 8 on the East Side, the unburned woods on the left side of the road are dark and dense, choked with a tangle of underbrush. Few wildflowers grow there. Without fire, these woods are out of whack.

On the right side of the road, where the woods have been burned, there’s little underbrush. The woods are open and light, and there are many more different kinds of plants.

“It’s a much more diverse ecosystem,” Dreisilker says, “because we've given that plant community back one of its most important ingredients, which is fire.”

To enjoy the benefits of prescribed burns, take a stroll between late March and early May along the trail between Parking Lot 11 and Big Rock Visitor Station on the Arboretum's east side. It’s a hotspot for spring wildflowers, with bloodroot, Dutchman’s breeches, trillium, bellwort, wild phlox, and sweeps of Virginia bluebells.

That area was burned several years ago, Dreisilker says, and the native wildflowers responded. The effect of fire, he says, is to allow the whole woodland plant community to thrive.

Frequently Asked Questions

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