The science behind prescribed burns: Restoring native ecosystems through fire

The ground is black, quiet and still after a burn. The smell of smoke lingers in the air, and the landscape can feel almost unrecognizable, like a moonscape where life has been erased. But beneath that charred surface, something powerful is already underway. In the days, weeks, months and years that follow, the land reawakens.

Prescribed fire is one of the most important tools used by the Forest Preserves of Cook County to care for prairies, woodlands and savannas.

“Prescribed burning is a really critical piece of our management,” says ecologist Anna Braum. “Most of our ecosystems here are fire adapted. That means they depend on fire to be sustained.”

In the days immediately following a prescribed burn, the most important changes are happening out of sight. With the layer of accumulated plant material, or thatch, cleared away, sunlight reaches the soil surface and warms it faster in the spring. That simple shift jump-starts the growing season. Within weeks, new growth begins to emerge, often earlier and more vigorously than in unburned areas.

But the real transformation does not happen in a single season. In most cases, it takes repeated burns over years to fully reshape the land.

Without fire, many local habitats begin to close in. In prairies, shrubs and woody species like buckthorn, honeysuckle and even aggressive native plants such as gray dogwood can spread quickly, shading out grasses and wildflowers. One burn can knock those species back, but they can retain the ability to resprout using reserves stored in the roots. Repeated burns begin to change the balance entirely by eliminating small shrub seedlings and exhausting the seedbank.

“Our prairie plants have a lot of unique traits that show that they’ve evolved in this system,” Braum says. “One of the things that you’ll see in a prairie is that plants have these structures called basal buds, or a bud bank, which allows plants to regrow because their buds are usually near the soil surface and protected from the fire.”

At sites across the forest preserves, that long-term approach is already showing results. Areas that have been managed with consistent burning support far more diverse plant communities than those that have gone without fire. In high-quality prairies like Somme Prairie Nature Preserve, ecologists can find up to 30 species within half a square meter.

“The site is very remarkable,” says Braum. “It’s been stewarded since about 1977 and has high quality mesic prairie and wet mesic prairie, which we have very little left of in the state.”

Some native species were never completely gone. They were simply suppressed, unable to compete for light and space. After several burn cycles, they begin to rebound, flowering more abundantly and spreading across the landscape.

“They may not flower because they’re shaded out,” Braum says. “There might be chemicals in the soil that inhibit their growth or germination. So, we’re just seeing a much healthier plant community after a burn.”

This process takes time and careful planning. Not every area is burned every year. Resource management staff rotate burns across the landscape, allowing wildlife to move between areas.

The flames may only last a few hours, but their impact continues long after. In the forest preserves, fire is not an end. It is the beginning of renewal.