If you’ve walked around North Pond over the past couple weeks, you may have noticed blackened areas and the faint smell of smoke— the result of a prescribed burn performed by the Chicago Park District and their natural areas contractors. Though the aftermath may appear somewhat haphazard, the Park District performs intentional, or prescribed, burns on reconstructed habitat throughout the city for several specific reasons owing to the natural history of fire in our region.
Our native ecosystems evolved with fire. Before humans harnessed it, fire, in the form of lightning strikes, altered the landscape, culling certain species and allowing others to flourish. The mighty oak, keystone tree of our state’s woodlands and prairies, has thick, corky bark that makes it impervious to flames. While other trees scorch, the oak thrives on their ashes. Without adequate fire, in fact, our robust oaks can be choked by faster growing trees.
But controlling unwanted trees and shrubs isn’t fire’s only role, and in urban areas mechanical or chemical methods of eliminating woodies are usually more practical since fire cannot be used to its full effect without concern for air quality and public safety. So what can we do with this constrained version of fire and how might it benefit our natural areas?
One technique often employed in restored and reconstructed prairies is called mosaic burning, a version of fire application that aims to create a variety of small areas with different fire histories to increase heterogeneity overall. The idea being, different types of habitat support different species and the greater the diversity of plant and animal species, the more resilient the ecosystem is.
Mosaic burning is also a compromise between the desire for greater ecosystem health and the realities of a densely populated area. Several factors influence where, when, and to what extent one can burn— wind direction, human curiosity, fuel load, moisture level, to name a few. Intensity must be carefully limited due to the immediate surroundings and many a burn must be cut short because of only a slight shift in the breeze.
When conditions do allow for fire, the burning that occurs can benefit the landscape in a few ways. The singeing of duff, or dead vegetation, can alter soil’s nutrient availability while also allowing more light to reach the ground. Increased sun penetration enhances microbial activity, encourages rooting, and allows for seeds requiring light to germinate. The patchiness of the burn helps create different habitat conditions to support a greater diversity of animals and plants.
The benefits of fire have been known for thousands of years, though sadly, our recent history has instead inspired fear and rejection of this powerful tool. The burning of our early wooden city negatively shaped attitudes toward fire to this day, to the detriment of what remains of the prairie state. Prescribed burning, like mowing or grazing, is but another method of modifying the landscape— for agriculture, hunting, wildfire management, and ecological restoration.
