By Greg Hoch
— Any fan of 19th century Midwestern history will note the numerous references to prairie fires.
They will also note that most of these fires were in the fall, especially October. Today, most prescribed fires for wildlife habitat management are conducted in April.
The tallgrass prairie may be the most fire-dependent ecosystem on the continent. Without fire, the rainfall is high enough to support trees. Because the first explorers to western Minnesota reported treeless landscapes, we can conclude that fires were frequent. Indeed, many historical references describe annual fires. Today, most management fires are conducted at four to ten year intervals.
Out West, despite what Smokey the Bore says, lightning starts most fires. Lightning storms in the Midwest are almost always accompanied by heavy rain. It’s not unusual to walk hilltop prairies after a storm and find a three square foot patch of black ash. Lightning hit, ignited the grass, but was immediately put out by the rain. If lightning caused prairie fires, they would occur in the spring and summer when thunderstorms are most common.
Based on the frequency and season of prairie fires in the prairie, we can conclude that Native Americans started the vast majority of these fires. This makes perfect sense if we consider why they lit many of these fires, hunting. They lit lines of fire upwind of a herd of bison, elk, or deer to force them into a river or valley for waiting hunters. Other times they would circle a herd with fire, concentrating the animals. Most hunting was done in the fall when the animals were fattest after eating all summer, the meat could be easily preserved in the cooler temperatures, and food could be stored up for the long winter ahead.
Minnesota’s prairies suffer a number of modern-day ills. Some prairie are simply lost to the plow. Other prairies are threatened by invasive species, which often lowers the diversity. Trees have invaded many prairies, which completely changes their character and dramatically lowers the suitability of these areas for songbirds and gamebirds. There is a large body of scientific literature showing that nesting success among waterfowl, gamebirds such as pheasants and prairie chickens, and songbirds decreases dramatically when trees invade into the prairie.
Mechanically removing trees from wildlife lands can be very costly, requiring heavy equipment and gallons of chemicals. The best management for invasive plants is prevention. The best way to keep trees out of the prairie is fire.
Some people see fire as removing nesting cover, especially for gamebirds. That’s true for the year of the fire. However, with management for prairie wildlife, it’s often about short term losses versus long-term gains. The removal of nesting cover, and trees, with fire in one year will greatly increase the quality of the nesting habitat over the next several years.
Lack of fire across Minnesota’s grasslands is hurting wildlife more than the periodic prescribed fires harm them. Fire, spring or fall, will always benefit prairie wildlife in the long term.
Greg Hoch is a prairie habitat evaluation ecologist with the Minnesota Department of Natural Resources stationed at the Farmland Wildlife Research Unit in Madelia.