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Fire: A Prairie’s Immemorial Ally

A crash of thunder, a bolt of lightning: a stray spark ignites a dry prairie and soon flames flicker, growing larger and brighter as a light breeze breathes energy into the fire. Untamed, it is certain to consume the dry grasses and plant matter that cover the prairie floor, raging on until there is no more fuel to burn. Perhaps the fire runs up against a lake, a river, or stream. Or perhaps it is doused by an extreme downpour of rain.

Leaving behind a singed and charred prairie, days later the wildfire is but a distant memory. New growth sprouts from the ground, and a coat of brilliant green paints the prairie canvas again.

For generations, wildfires were a natural process of renewal. But as more land became developed and the prairie landscape more fragmented, people and their possessions were caught in the paths of these destructive flames. The tragic Peshtigo Fire and the Great Chicago Fire (on the same night in 1871) claimed millions of acres and thousands of lives, giving rise to fire cessation and prevention, including Smokey the Bear decades later. To the general public, fires were a threat. This sentiment greatly limited the number of wildfires that naturally maintained the landscape.

Aldo Leopold participates in a prescribed burn at the University of Wisconsin-Madison Arboretum.

It was during this very time period that Leopold lived, yet he understood the value of fire to the prairie. In “Odyssey,” he explains, “Fires thinned its grasses, but they thickened its stand of leguminous herbs: prairie clover, bush clover, wild bean, vetch, lead-plant; trefoil, and Baptisia, each carrying its own bacteria housed in nodules on its rootlets. Each nodule pumped nitrogen out of the air into the plant, and then ultimately into the soil. Thus the prairie savings bank took in more nitrogen from its legumes than it paid out to its fires. That the prairie is rich is known to the humblest deermouse; why the prairie is rich is a question seldom asked in all the still lapse of ages.”

Fire is an essential element aiding in the health of several ecosystems, namely prairies, savannas, chaparral, and some woodlands and wetlands. All fires need fuel to burn. Dry grasses, dead plant matter, and leaf litter build up on the floors of prairies and woodlands, blocking out sunlight necessary for new plant shoots. In addition, a deep layer of leaf litter makes foraging for nuts and other food more difficult for some wildlife. This low layer of flammable matter is cleared away as fire consumes it, which also lessens the likelihood of future wildfires.

In these fire-dependent habitats, native plants developed adaptations to withstand fire. For example, in the oak savanna, bur oaks have a thick, corky bark that barely singes. Leopold likened it to armor. “Bur oaks were the shock troops sent by the invading forest to storm the prairie; fire is what they had to fight. Each April, before the new grasses had covered the prairie with unburnable greenery, fires ran at will over the land, a sparing only such old oaks as had grown bark too thick to scorch.” Bur oaks, like other fire-dependent trees, also shed their lower branches as they grow, keeping leaves high above the flames.

Wildflowers and other plants store energy below the soil in their roots. A fire provides important nutrients that encourage fervid re-sprouting. In fact, some plants and trees are dependent on an extreme heat source to unlock seeds from pods or pine cones in order to finally germinate.

Students learn the techniques of prescribed fire while executing a burn of the prairie in front of the Leopold Shack.

Fire is also an efficient means of suppressing invasive species, which are often not tolerant of fire. Even for woody shrubs that may not fully burn, fire drastically sets back growth with a top-killing effect from the burn.

As for the wildlife, while they don’t directly benefit from fire, it does reward them with the spoils of abundant food sources and easier foraging. And, typically, they aren’t harmed by fire. Birds and large mammals have the ability to escape, while smaller mammals may burrow underground. Similarly, amphibians will burrow under wet mud or take to a water source.

Today, an entire science is dedicated to wildfire and its effects on the natural environment. Through a deeper understanding of this natural phenomena, prescribed fire has become a standardized land management practice. Though ever-evolving, as is fire itself, fire ecology clearly recognizes its value and role as the prairie’s immemorial ally.


Did you enjoy this article? It appeared in our Summer 2018 issue of The Leopold Outlook. Become a member and get the Outlook magazine delivered to your mailbox!

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