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Title: Candidate perennial bioenergy grasses have a higher albedo than annual row crops in the Midwestern US

item MILLER, JESSE - University Of Illinois
item VANLOOCKE, A - Iowa State University
item GOMEZ-CASANOVAS, NURIA - University Of Illinois
item Bernacchi, Carl

Submitted to: Global Change Biology Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/14/2015
Publication Date: 11/1/2015
Citation: Miller, J.N., VanLoocke, A., Gomez-Casanovas, N., Bernacchi, C.J. 2015. Candidate perennial bioenergy grasses have a higher albedo than annual row crops in the Midwestern US. Global Change Biology Bioenergy. 21:4237-4249.

Interpretive Summary: Bioenergy crops are projected to have a significant impact on the environment. The majority of this impact is associated with using fewer fossil fuels which will help to offset rising atmospheric carbon dioxide that is driving global warming. The use of perennial grasses instead of annual row crops for bioenergy production are also projected to lead to changes in the amount of radiation reflected from the land surface. This can impact local temperatures as higher reflectivity associated with perennial grasses are projected to have a net cooling effect. This study provides a direct comparison of surface reflectivity for the perennial grasses miscanthus and switchgrass relative to maize. The study shows that perennial grasses reflect slightly more radiation than row crops but that the interaction with climate is not straight-forward. For example snow cover is shown to reverse this trend with the tilled row crop fields showing more uniform snow cover and thus having higher reflectivity (and therefore more cooling potential) than perennial grasses. This study is the first of its kind to provide direct data collected on these species in a comparative manner. In addition to assessing the consequences of land use changes for bioenergy production, this is an important dataset for ecosystem model validation and parameterization.

Technical Abstract: The production of perennial cellulosic feedstocks for bioenergy presents the potential to diversify regional economies and the national energy supply, while also serving as climate ‘regulators’ due to a number of biogeochemical and biogeophysical differences relative to row crops. Numerous observationally and modeling based approaches have investigated biogeochemical tradeoffs, such as increased carbon sequestration and increased water use, associated with growing cellulosic feedstocks. A less understood aspect is the biogeophysical changes associated with the difference in albedo (a), which could alter the local energy balance and cause a local to regional cooling several times larger than that associated with offsetting carbon. Here, we established paired fields of miscanthus and switchgrass, two of the leading perennial cellulosic feedstock candidates, and traditional annual row crops in the highly productive “Corn-belt” of central Illinois. Our results showed that perennial biofuel crops had an overall higher a than current agricultural crops but there was a strong seasonal pattern. Perennials had consistently higher growing season a but lower winter a than annuals, particularly when snow was present and especially in years with the greatest number of days with snow cover. Overall, these changes in a result in an average net reduction in annual absorbed energy of about 4 W/m2 for switchgrass and 8 W/m2 for miscanthus relative to annual crops. Therefore, the conversion from annual row to perennial crops alters the radiative balance of the surface via changes in albedo and could lead to regional cooling.