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Reply to Kline et al.: Cropland data layer provides a valid assessment of recent grassland conversion in the Western Corn Belt

2013; National Academy of Sciences; Volume: 110; Issue: 31 Linguagem: Inglês

10.1073/pnas.1307594110

1091-6490

Christopher K. Wright, Michael C. Wimberly,

Forest Biomass Utilization and Management

Kline et al.(1) pose a series of "what-if" scenarios intended to cast doubt on our (2) findings.These scenarios arise from a critical misreading of our paper and misinterpretation of the US Department of Agriculture's Cropland Data Layer (CDL).First, we did not include alfalfa (Medicago sativa), a perennial cultivated-hay legume, in our definition of grassland (2), contrary to Kline et al.'s (1) claim.This error propagates throughout their analysis.Our grassland definition combines all CDL grass-dominated land cover types within the Western Corn Belt (WCB).We agree that grassland increases have occurred in the WCB (3).However, Kline et al. ( 1) do not address important subregional variability.By our grassland definition, we find a 2.1 million ha increase in CDL grassland west of the 100th Meridian, a commonly accepted (if somewhat arbitrary) transition to the arid west.East of the 100th Meridian-where the overwhelming majority of corn/soy production occurs-total grassland area decreased by nearly 800,000 ha from 2006 to 2011.Unfortunately, grassland increases in one subregion cannot mitigate losses in distant locations.Kline et al.(1) find a 1.2 million ha decrease in fallow/idle cropland, suggesting that increased corn/soy cultivation could be explained by expansion onto idled land.However, of the nearly 800,000 ha of grassland conversion we documented (2), only 154,000 ha originated from the CDL fallow/ idle class.Inspection of the CDL shows that nearly 1.2 million ha of fallow/idle lands in 2006 were reclassified as other grassland