THE EFFECTS OF WILDFIRE ON GRASSLAND WILDLIFE

Last week, a wildfire originating on I-25 burned 42,000 acres of grasslands in the vicinity of Chico Basin Ranch, destroying two dozen homes. Several pastures on the ranch were wholly or partly engulfed in flames. While fire has a reputation as a destructive force, in fact, it often functions to maintain ecosystem balance on grasslands. From the National Park Service: “Regular wildfires shape the makeup of vegetation by suppressing woody plants and favoring grasses. Because their growth structure is situated at or below the ground, and because fire moves quickly through grasslands, most grasses tolerate fire or even proliferate after a fire. Without fire, shrubs and trees would take over grasslands, effectively converting them to forest, and non-native vegetation would spread.” Below, natural historian and birder on the Chico Bill Maynard speculates on the potential aftermath of the 117 fire for the vegetation and wildlife of the ranch.

Before European settlers arrived in North America, native grasslands burned periodically, creating a mosaic of denser and less dense grasses where mammals and birds evolved with the habitat. The US Forest Service established a fire management policy, and many of us grew up with Smokey the Bear telling us that fires are basically bad. Smokey the Bear’s message resulted in the suppression of all fires. Fire suppression results in a build-up of fuels, eventually leading to catastrophic fires like the 117 Fire, the destructive fire last week along Hanover Road and on part of Chico Basin Ranch.

Two common birds on the Chico’s grasslands are Western Meadowlark and Horned Lark. Western Meadowlarks need dense grasslands with a mixture of cholla or sand sage in which to nest. After a grassland fire, Western Meadowlark numbers plummet, but bird numbers and the habitat fully recover the third year after the burn. Horned Larks benefit from fires, that species preferring short, open grasslands for their ground nests. When vegetation gets denser, such as following last years’ numerous April rains, Horned Lark numbers decrease.

A Western Meadowlark (top) and a Mountain Plover (bottom) in their respective preferred habitats of dense and sparse grasses.

In the grasslands in northeastern Colorado, research has shown the effects of prescribed burning on the declining bird species, Mountain Plover. The same study evaluated the affects of doubling the number of cattle in a grassland area and its effects on Mountain Plovers, and thirdly, the study evaluated the comparative effect of black-tailed prairie dog colonies and their relationship to breeding Mountain Plovers. The study concluded that grassland fires and prairie dogs maintained the habitat requirements of nesting plovers. Mountain Plovers (bare ground specialists and not found in the mountains) require at least 35% bare grounds and a flat grassland habitat with grass species less than three inches in height. When plague severely reduced black-tailed prairie dog numbers on the Chico a few years ago, Mountain Plovers disappeared as breeders when the grasses became too tall. Due to the absence of browsing by prairie dogs, even the shortest grasses grew too tall to attract that species as breeders.

Grassland fires manipulate the shortgrass prairie to become a mosaic of differing grass heights, each grass height and density suitable for a different group of breeding birds. It will be interesting to see if Mountain Plovers return to Chico, possibly selecting this year’s burned grassland areas as next year’s breeding sites. Spring and late summer rains should provide the moisture, while the burned vegetation will releases nutrients back into the soil in the form of ash needed to turn today’s blackened prairie back to a brilliant green.

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