Thursday, August 22, 2013

Prairie Restoration

Moore Memorial Park, Ames, Iowa (January 14, 2012)

I wrote before about Moore Memorial Park in Ames. The park is located vey close to my house, and is the place where I usually walk Kero in the morning. Situated on land donated to the city by Fern and Bertha Moore, the park occupies what once was a dairy farm. It is crossed by a creek meandering in between slow rolling hills.

A neat thing in the park is that a sizable portion of it is being kept as restored prairie. Tall grass prairie once occupied most of the US Great Plains, the land that was roamed by bisons and the nomadic tribes that were hunting them. Most of this prairie has now disappeared, converted into industrial farms. Illinois alone once held over 35,000 square miles of prairie: today the grand total for the state is about 3 miles of original prairie. An inland sea of grasses and forbs (most wildflowers and legumes), the prairie was a hotspot of diversity, and was crucial to preserve the fertile topsoil from erosion, store water during excessive rainfall and preserve life during droughts, temperature extremes and native insects pests. It is not by chance that, once the prairie was finally removed at the end of the XIX century, a severe drought in the '30s transformed the midwest into the Dust Bowl, when 75% of the topsoil was blown away, causing the economic collapse of the region.

How do you restore a prairie? You use the same force of nature that have acted on it for eons: fire. Prairie grasses and forbs are adapted to the periodic fires that naturally swept the prairie, by having deep root systems that can survive a grass fire. Other invasive species (including bushes and trees) are not. By applying periodic burns (every few years), one can selectively remove the invasive species making space for the native plants (and naturally fertilizing the soil in the process). At every passage the fraction of native, fire resistant, plants will increase, until the ecosystem is restored to a status as close as possible to the native grassland. The photo above was taken in the middle of winter (two years ago, when unfortunately we didn't have much snow at all, prelude to a severe drought during the summer). As you can see all the grass is very dry, perfect fuel for fires triggered by chance lightening. Or by the park caretakers, that at the beginning of spring walk around yielding flame throwers, setting everything on fire, to let a renewed prairie emerge from the ashes.

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