Recent Land Use Change in the Western Corn Belt Threatens Grasslands and Wetlands

The recent boom in the biofuel industry, in part due to incentives that promote the conversion of grassland to corn and soybean cropping, is reshaping the landscape of the US Corn Belt. Wright et al. (2013) sought to study the extent to which this land use conversion is occurring, and what its implications may mean for the environment.  The researchers used the National Agricultural Services (NASS) Cropland Data Layer (CDL) to examine the rate at which grasslands have been converted into corn/soy cultivation over five states of the Western Corn Belt: North and South Dakota, Nebraska, Minnesota, and Iowa.  The authors considered the agronomic and environmental attributes of lands on which grassland conversion was occurring, as well as the effects on nearby waterfowl nesting sites, and included these in the results as well.  The results of this study show that the rate at which land was being converted has not been seen in the US since the advent of the mechanization of US agriculture in the 1920s.  The implications of this rate are bleak as it threatens waterfowl populations, soil quality, and water resources.  The authors recommend we shift to biofuels produced from perennial feedstocks, as these fuels have desirable traits with respect to net energy and greenhouse gas balances and wildlife conservation. —Anthony Li
Wright, C. K., Wimberly, M. C., 2013. Recent land use change in the Western Corn Belt threatens grasslands and wetlands.  Proceedings of the National Academy of Sciences of the United States of America published ahead of print February 19, 2013

The authors acquired land cover data from 2006 to 2011 of the Western Corn Belt from the NASS CDL.  They selected this year range because the extent of the data recording goes back to 2006. The NASS CDL uses land cover data acquired from satellite imagery and maps agricultural land cover at a very high crop-type specificity.  Using the 2006 NASS CDL data and comparing it with the 2011 NASS CDL on a per-pixel basis allowed the researchers to observe a general grass-dominated land cover be converted into a general corn/soy cultivation land.  In order to see if the land use data derived from the NASS CDL was representative of long-term land cover change region-wide, they performed a trend analysis of grassland conversion in North Dakota and Iowa.  The analysis showed that the data were representative.  The researchers also took note of the agronomic and environmental attributes of the lands in which NASS CDL recorded data on.  Lastly, the authors examined the relationship between grassland conversion and lands protected under the Conservation Reserve Program (CRP).  The CRP “pays farmers to establish and maintain grassland cover on retired cropland in exchanged for a fixed rental payment over a fixed period,” but in recent years with the rise of corn and soybean prices as well as a projected consistently high commodity prices, more farmers have not been renewing their CRP contracts.  By examining this relationship, the authors were able to see which recently converted areas were formerly protected by the CRP, showing some insight in the farmer’s reasons for changing crop.
The results showed that across the Western Corn Belt, there was a net decline in grass-dominated land cover totaling near 530,000 ha, more than 1.3 million acres, from 2006 to 2011.  This change in land cover was concentrated in South Dakota and Iowa.  The rates at which grassland is being converted to corn/soy is comparable to the deforestation rates in Brazil, Malaysia, and Indonesia.  The authors make the comparison that the current rates of grassland conversion have not been seen in the Corn Belt since the advent of agriculture’s mechanization in the 1920’s.  Grassland conversion is also occurring dangerously close to the Prairie Pothole Region, a wetland region that acts as a climate-change refugia for North American waterfowl.  The current rate of grassland conversion threatens one of the few breeding grounds of waterfowl.  The authors found that grassland conversion was concentrated on relatively high quality lands in Minnesota and the Dakotas, suggesting that the local landowners are seeking higher rates of return by swapping to corn and soybean cultivation.  This trend has become increasingly consistent due to the emerging market of corn/soy production and its rate of return.  In Iowa, they found grassland conversion was occurring on less suitable land, reflecting the lack of high quality land for soybean/corn cultivation.  Similar to Iowa, Nebraska was also shown to have used unsuitable land for crop production, suggesting that both these states will have to acquire more resource-intensive irrigation practices to sustain the soy/corn crops.  The authors also predicted that fewer landowners will be renewing their CRP contracts as the higher rates of return for soybean/corn cultivation is more economically viable.
While this paper shows the rate at which the biofuel industry has grown, it also shows the daunting implications for such a growth. Grassland conversion into corn/soy production is characterized by high erosion risk and vulnerability to drought.  This grassland conversion also threatens waterfowl populations, as the soy/corn fields encroach upon diminishing waterfowl breeding sites.  The grassland conversion also effects the soil’s carbon sequestration ability.  The authors predict that with the reductions in soil sequestration caused by grassland conversion, “more than three decades of biofuel substitution” will be required to counteract this.  In the face of all this the researchers suggest an alternative, saying that biofuels derived from perennial feedstocks are more efficient with respect to net energy and greenhouse gas balances as well as wildlife conservation.

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