Burn & Rebirth

By Katherine Millett

Even before the smoke clears, the prairie buzzes with activity.

 

In my head, I know that burning a prairie in spring or fall kindles the health of the native ecosystem. I know that Native Americans once set fires in places where lightning had not already done the job. But in my heart, I still wonder how in the blazes fire sustains life.

Early last spring, I stood by a field of charred stubble at The Morton Arboretum, incongruously labeled “Schulenberg Prairie.” (“Schulenberg Ashes” would have been more appropriate.) As summer took its course, the phoenix rose. The stubble re-made itself into a thriving, buzzing community of Latin names—hundreds and thousands of plants, animals, fungi, and more, diverse in their height and color, texture and motion.

A more trusting person would have been convinced of fire’s virtues by that miracle alone, but growing up in Colorado, I had heard too many dire warnings from Smokey Bear. The fire monster lurked beyond the tents at every campground in the Rockies. Fire was just waiting for one tiny match, one smoldering marshmallow, to go wild and consume all the green conifers on our dry mountains.

Then I moved to the much wetter world of Illinois. In Chicago’s wild preserves, I was told, land managers regard fire as a kind of therapy. But what happens exactly, that makes fire so beneficial? Why do some plants survive, while others are destroyed? What happens to seeds and mushrooms? Where do rodents go, and what becomes of rabbits and birds? From an ant’s point of view, how will life be different after a fire?

Last fall, I tagged along with Chris Hauser, an ecologist and burn-crew leader for the Forest Preserve District of Kane County, to watch a controlled burn. Maybe seeing the visible part of the drama would help me understand the invisible world too, the micro-dramas that play out under the rocks and inside the stems before, during, and after a fire.

Hauser met his crew, all clad in yellow suits and visored helmets, to burn around Nelson Lake at Dick Young Forest Preserve, a wetland-prairie ecosystem in Kane County. Spring-fed and sparkling-blue, the lake was circled by three years’ growth of invasive cattails, nonnative reed canary grass, and brush. Only a few native flowers and grasses poked through the “duff,” the thick, packed mat of grass stems, cattails, and leaves covering the ground like a suffocating blanket.

The purpose of the fire, Hauser explained, was in part to burn the duff off the mineral soil and take down most woody plants. Duff blocks the sun’s rays and brush casts shade, but burning restores the sun’s energy to the soil. It’s not the immediate heat of the fire that makes the difference; it’s the heat of the sun, later.

I imagine it as giving the land an inoculation. Like the prick of a needle, the burn “hurts” for a minute, temporarily setting back some plant and animal species, but then it makes the whole system healthier. It strengthens species that make up a healthy community, so they can compete successfully with species that don’t. And the species that belong, according to ecologists, are those that have lived here as long as 10,000 years, side by side with the bison, and have been evolving in fire-adapted landscapes for hundreds of millennia.

Fire and Seeds

I watched Hauser walk decisively down a slope of reed canary grass, into the cattails. He strode among stems, painting the ground with drips of burning kerosene from his torch can. On the cattails’ fluffy brown heads, tiny seeds—a million per spike—exposed themselves to passing gusts of wind. In a rush of flame, the cattails were quickly reduced to ash.

Their seeds, which aren’t fire-adapted, did not survive. But some seeds actually need fire or smoke to germinate. Kay Havens, who directs seed research at the Chicago Botanic Garden, says fire makes hard-coated seed casings explode. “This is true for the mallows, including a rare form called Kankakee mallow,” she says. “They crack during a fire and open when moisture gets into the cracks. Other kinds of seeds need smoke. If you expose purple coneflower seeds to smoke, for example, more of them germinate, and they germinate faster than they would without smoke.”

It’s easy for a person to ask, “What does smoke do to a seed?” but sometimes the answers haven’t been revealed. “We know that it has something to do with a chemical called butenolide,” says Havens, “but we don’t understand the mechanism yet. We’re working on it.”

Havens invites me to think about fire not as a destructive force, but as an environmental variable. Fire begat the plants that live in tallgrass prairie ecosystems and caused them to develop survival traits.

“There are basically two strategies for a plant to survive,” says Havens. “One is to be a re-seeder, and the other is to be a re-sprouter. Many of the forbs, or wildflowers, produce fire-resistant seeds. All of the prairie grasses, from big bluestem to Indian grass, are re-sprouters. That means their growing tips stand close to the ground. When fire moves through, it burns off the upper parts of plants but leaves the tips unharmed, to grow again.”

Hauser excitedly tells me that the wind’s speed and direction are perfect for today’s burn. Methodically, he torches a rectangular area to make a fire break and sends the crew upwind, to the end of the lake, to set a fire that will burn back along the shoreline and stop at the fire break.

Within minutes, a cloud of smoke blocks the morning sun. Habitat is burning for a cohort of animals, the ones that haven’t migrated or dug in for the winter. What happens to them?

“They run or fly away, take refuge in some nearby place that hasn’t been burned,” says Bill Glass, staff ecologist at the Midewin National Tallgrass Prairie in Will County. “When we burn, we never get every part of a grassland. There are always strips or islands that don’t burn.”

The result is a mosaic of burned and unburned patches and corridors. These give wildlife—including deer, coyote, and other larger animals—choices for refuge. Sure enough, during the day I’m startled as four rabbits zoom out of the burning grasses, down the trail, and into the woods. Each hops within touching distance, judging us to be safer than fire—or something else.

Predators have become wise to the ways of fire. “I’ve seen hawks circle at the edge of a burn,” says Hauser. “They seem to be waiting, watching for animals to run out of the fire.”

Among the most vulnerable small mammals are voles. “Fire kills some and drives others away,” says Hank Howe, a biologist at the University of Illinois at Chicago who studies voles in prairie test sites. “They flee when there’s no cover, because they need hidden runways to protect themselves from predators.”

Fire controls the number of voles, which in turn directly affects prairie composition. Voles live almost everywhere except in some of Howe’s experimental tallgrass plots in Wisconsin. By fencing voles in or out of planted plots, he has tested their dietary preferences.

“They eat what they like and pretty much eliminate it,” he says. “Among their favorite foods are the big, flat seeds of rosinweed, a yellow-flowering relative of compass plant and prairie dock. By eating big seeds, voles encourage the growth of plants with small seeds. So once rosinweed thins out, small-seeded plants have a better chance, like asters and yellow coneflowers. The ‘echo effect’ of this practice can change a plant community for years.” Over time, says Howe, voles kept in average numbers increase the variety of species by about a third.

Symbiotic Relationships

One of the key actors in prairie rejuvenation never appears on stage. It stays in the moist, clay soil. Mighty but lowly, fungus lives symbiotically among the roots of prairie plants.

“Prairie food webs are dominated by fungus,” says Mike Miller, a soil ecologist at Argonne National Laboratory in DuPage County. (Conversely, bacteria drive the life cycle in farmlands.) Miller is talking about fungi in their long, stringy underground forms, the hollow threads called “hyphae” that latch onto plant roots and venture out from there. They explore the soil for nutrients such as phosphorus and nitrogen and transport them back to their host plant. In return, the plant gives the fungus carbon to grow.

Together, these rich tangles of roots and fungus, known as mycorrhizae (“fungus-roots”), depend on fire. “Only when the soil gets above 50 degrees Fahrenheit do fungi grow to any significant extent,” says Miller. “They stay dormant in winter, and they grow much faster in the spring if the ground above them has been burned.”

As hyphae grow, so grow tiny grazers in the soil. “They love hyphae!” says Miller. “Mites, the springtails and millipedes —this is their food. These guys are chewing below ground while other animals are eating the same plants above ground.”

Though soil is an excellent insulator, insects and microscopic organisms in the duff and top centimeter of soil usually succumb to the heat. Lucile Rice, a biologist from Utah, traveled to Illinois in the 1920s to observe the effects of spring fires on animal communities in Illinois prairies. She found that spiders, which live primarily in surface areas, are drastically reduced by fire. (They do eventually return.) Mites, which constitute much of the biomass in prairie soil, are also hit hard, their numbers reduced by half, though they recover in about three years. Beetles, differently adapted, find places to hide in grass tussocks. About 85 percent of beetles survive a fire, and they recolonize very quickly after the flames die down. Many insects thrive after fires. Grasshoppers increase in both numbers and diversity. Ants go crazy, scurrying back and forth between burned and unburned areas by the thousands, building their colonies and their population.

Of the 95 ant species in Illinois, says Laura Rericha, a naturalist with the Forest Preserve District of Cook County, 40 live in prairies. “They need fire,” she says, “because they need moist, organic soil with lots of decomposing plant material. They sleep through the winter, underground or in decaying wood, then wake up when the ground warms.”

Anticipation of Rebirth

Late in the afternoon, Hauser packs up the drip cans and water tanks, arranging them in the back of his truck. The smoke has cleared, the blue sky has returned, and the sun is sinking. He looks over the mosaic pattern of black patches and green-brown grasses left by the burn.

“It’ll be fun to come back in the spring and see what happens,” he says. “Some of the first flowers will be clumps of marsh marigolds, greening up faster and blooming a lot better because of the fire. The cattails will be back, but they’ll be mixed with native lake sedges, bulrushes, and bur reeds. I’ll probably see flocks of flickers and robins fly in to scrounge in the soil for food.

“If I see a line of bare soil with all kinds of things growing around it, I’ll know that’s where a log burned, slow and hot enough to kill whatever was living underneath it. It makes me think of what’s happening underground with the mycorrhizae, the insects, and the microbes.”

Beyond view in the blackened marsh, insect eggs cling inside the stems of compass plants and prairie docks. Felled by the burn, these plants still play their part. They host only certain insects, which are highly selective when it comes to choosing plants to help them survive both the fire and the winter.

“There are so many insects we know almost nothing about,” says Hauser. “We give them names; we may know when they fly, reproduce, and lay eggs, but that’s about it.”

Yet careful observers keep learning more, piecing together bits of the plot until they understand. Having learned from them a little about the subtle complexity of the prairie, I sense some of what I can’t see as I walk through a forest preserve on a winter day, including the far-reaching influence of fire. Beneath the drooping grasses, inside the hollow stems, under the charred cattails, the natives are restless.

Related Articles:

Born to Burn, CW, Summer 1998

Chicago Wilderness 2006 Burn Report, CW, 2006

Burning in the Rain, CW, Fall 2000

The Burn that Wasn't, CW, Fall 1999