St. Croix WMD |
Prairie Fires and Grazing
Fire was a natural event on the prairie often started by lightning. In western Wisconsin, fire was the dominant force in shaping the prairie and oak savanna. This area receives enough rain to support trees, but fire and periodic drought helped keep the forests from expanding into the grasslands. Historically, portions of St. Croix, Dunn, and Polk Counties were dominated by prairie and wetlands. The geology of this area of the state was shaped by the glaciers. As humans settled and the prairie was broken and fragmented, fires could not carry across the expanses they once did. Whether it was fire or intense short term grazing by nomadic bison, grassland plants evolved a dependence on frequent disturbance. Today, fire, haying and grazing are used to stimulate native grasses and forbs. The District has to rely on local farmers and ranchers for assistance with haying and grazing. Fire can be an inexpensive and controlled way for us to successfully manage a prairie tract.
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Prescribed Fire as a Management Tool
Fires are conducted by highly trained staff using a variety of specialized equipment such as fire engines, drip torches, all terrain vehicles and water pumpers. Conditions like wind direction, wind speed, temperature, relative humidity, safety and smoke dispersal have to meet a designated set of criteria called the "prescription". A plan must be written that sets those criteria and provides guidelines for potential issues so that the fire can be conducted safely.
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Large tracts are frequently divided into smaller burn units that are more manageable as well as biologically beneficial. Leaving a portion of a tract unburned provides a refuge for animals and insects that will return to the burned area as it begins to grow again. A burn unit is typically burned every three to seven years. When establishing new grassland, it can be beneficial to burn it both the third and fifth year after seeding. Grasslands are burned primarily in the spring and fall but may be burned in summer also. The timing of the burn depends on the objective for the tract of land. Some of our burn objectives include: stimulating grassland seeding or native prairie, setting back the growth of invading trees, removing plant litter that has built up over time, reducing fuels (layers of plant growth) around towns, rural homes and barns, and stimulating grassland plant seed production.
Prairie plants evolved with fire and grow vigorously and produce more seed following a fire. They grow more robust after a fire because the plant litter has been removed from the soil surface, which results in higher soil temperatures and increased nutrient availability. Prairie animals also evolved with fire and usually escape unharmed. Burrowing animals seek shelter from the fire in their underground burrows. Birds can fly and animals can run away from an oncoming fire. Some nests are destroyed by fire, but ground nesting birds like waterfowl and songbirds have evolved with fire and predation. When a nest is lost, these species will usually renest. Because predation is so high on ground nesting birds, re-nesting is the only way these species have successfully maintained their populations over time. Nesting cover and food provided by the robust and diverse plant growth that follows a fire generally benefits ground nesting birds for four to six years after a fire.
