Think of deforestation and images of the Amazon river basin stripped of trees are likely to come to mind. But the loss of wild lands and natural habitat to pastures and sprawling cities isn’t restricted to the jungles of South America. Before the colonization of North America, the Great Plains were a seemingly endless sea of grass that supported a complex ecosystem, but since the founding of the United States the vast majority has been converted to cropland and urban areas. Some undisturbed areas of tallgrass prairie remain, but open lands continue to be under pressure from farming and development interests.
Much of the change in the Midwest is conversion of grasslands to corn and soy production, often intended for biofuels production. Fulfillment of the U.S. renewable fuels mandate in 2012 required 13 billion gallons of ethanol and the total is set to rise to 14 billion — and this despite a severe drought that resulted in poor corn harvests last year. Beyond its negative impacts on species diversity and broader ecosystems, plowing undisturbed land has been shown to release carbon dioxide, one of the primary drivers of climate change that biofuels are in theory supposed to help address. This “carbon debt” can be overcome by replanting perennial crops, but it can take years.
A 2013 study published in the Proceedings of the National Academy of Sciences (PNAS), “Recent Land Use Change in the Western Corn Belt Threatens Grasslands and Wetlands,” looks at the rate and type of land conversion in the corn-growing areas of the Midwest and the impacts on erosion, wildlife and watersheds. The authors, at the University of South Dakota, note that “a recent doubling in commodity prices has created incentives for landowners to convert grassland to corn and soybean cropping.”
With 2006 a baseline, they used high-resolution imagery to assess groundcover change in the Western Corn Belt, which spreads over North and South Dakota, Nebraska, Minnesota and Iowa. The region contains the largest remaining stretches of grass-dominated land in the central corn-growing region and also overlaps with the endangered wetlands of the Prairie Pothole Region (PPR), an important refuge for North American waterfowl. Conversion through the 2011 growing season was recorded.
The study’s findings include:
- Between 2006 and 2011, nearly 530,000 hectares (1.3 million acres) of grass-dominated land cover in the Western Corn Belt (WCB) were converted to cropland. The majority was corn or soy production expanding onto “marginal lands characterized by high erosion risk and vulnerability to drought.”
- The conversion rate of grassland to corn or soy production is 1% to 5.4% annually in a large portion in the WCB. This rate is “comparable to deforestation rates in Brazil, Malaysia, and Indonesia, countries in which tropical forests were the principal sources of new agricultural land, globally, during the 1980s and 1990s.”
- More than 99% of tallgrass prairie present in the WCB before settlement has been converted to agricultural or other uses. What was once a tallgrass prairie of 12 million hectares (29.7 million acres) in Iowa has been reduced to 0.1% of its original, natural expanse.
- “Under the most likely climate change scenario for the Northern Great Plains, a 3 to 4 centigrade increase in mean annual temperature offset by a 10% increase in mean annual precipitation, much of the wetland habitat in the PPR is projected to be lost. High-quality waterfowl habitat most likely to persist under climate change is projected to be concentrated in South Dakota east of the Missouri River. However, this is precisely where grassland conversion in close proximity to PPR wetlands is most prevalent.”
- At the current rates of conversion, the “WCB is rapidly moving down the corn ethanol and soy biodiesel pathway.” Beyond the threat this constitutes to wetlands and biodiversity, it also would release significant quantities of carbon dioxide. “Even if recently converted grasslands were subsequently converted to perennial bioenergy crops, substantial carbon debts would still persist.”
As an alternative to conversion of grasslands to soy and corn for biofuels production, the authors suggest harvesting mixed prairie grasses to be used as a cellulosic biofuel feedstock. However, “the present study indicates that the window of opportunity for realizing benefits of perennial bioenergy crops may be closing in the WCB.”
Related research: A 2012 study in Nature Climate Change, “Impacts of Biofuel Cultivation on Mortality and Crop Yields,” examines the emissions of isoprene, a biogenic volatile organic compound, by the growth of bioenergy crops. Because isoprene has a significant effect on ground-level ozone concentrations — which can have adverse health effects, particularly during hot weather — crops that increase its presence can have a significant impact on human mortality and crop yields.
Keywords: greenhouse gases, renewable energy, water