Across our region, spring is often viewed as the burning season, as crews draft burn plans, prepare equipment, train new workers and create firebreaks. You may wonder how this came about. After all, North America’s indigenous peoples often set the prairie ablaze after the first frost of autumn, when dry biomass is at its peak, adding nutrients to the soil and revitalizing the earth. Remember that prescribed burns, started by humans, evolved largely out of necessity. Unlike in our Western forests, lightning rarely ignites prairie fires. How many times have you seen lightning without rain around here?
Okay, so why did we humans make the switch from fall to spring “cleaning”? One reason: Ring-necked Pheasants, a non-native species that requires special care, including tall grasses in which to winter and hide. Many prairie land managers succumbed to pressure from local hunters, whose hunting licenses often paid their wages. But there’s more to the story, and it revolves around another “migrant” from Eastern Europe — bromus inermis, or smooth brome, which is one heck of a plant.
In the early part of the 20th century, smooth brome found its way to the Midwest and managed to put down roots in every native prairie I’ve visited. Those roots typically strangle most neighboring plants. In fact, allelopathic species, such as smooth brome, inhibit the growth of all nearby plants. Nevertheless, they have their use. My grandfather planted brome in areas where weeds were a concern. The brome choked out the weeds, and his well-fed cattle were able to graze on the brome in a virtuous cycle that was both cost-effective and clever.
Now let’s get back to our question: Why burn prairie lands in the spring? Well, brome is a cool season grass, meaning that it greens up early, in cool weather, and does not do nearly as well in warm weather. The trick is to let the brome green up a bit — usually when it has grown three leaves — and then begin your controlled burn. This sets the brome back and encourages native, warm-weather-loving prairie plants to thrive and overtake the brome. Although these carefully managed fires don’t kill the brome, they do put a hurt on it.
That being said, many land managers, including the Pottawattamie County Conservation Natural Areas management team, still prefer prescribed burns in the fall, especially in woodlands and savannas.
So, now you know a little more about why we burn agricultural and prairie lands in the spring. But, if you put fire ecologists and entomologists in the same room and ask them to debate the advantages of spring and fall burns, the discussion will get pretty interesting pretty quickly.