|Mitchell, Robert - Rob|
Submitted to: Ecological Applications
Publication Type: Review Article
Publication Acceptance Date: 3/10/2010
Publication Date: 3/10/2010
Citation: Mitchell, R.B., L.L. Wallace, W. Wilhelm, G. Varvel, and B. Wienhold. Grasslands, Rangelands, and Agricultural Systems, Biofuels and Sustainability Reports, Ecological Society of America. 2010. Interpretive Summary: Sustainability occurs when a system has all of its components working nominally so that function can continue as long as resources are available for operation. Ecosystems are not so simple, however. We examine agro-ecosystems designed to grow feedstocks for the growing biofuel industry, particularly the production of ethanol. We focus on switchgrass, although other species may be used for the production of cellulosic ethanol including other monocultures or mixtures of native grasses. This field of study has grown tremendously since 2005, but, in the midst of all of these data, a common method of comparison between studies, a common method and models for LCA and a common set of variables to measure are missing. This makes large-scale comparisons difficult. Based on currently-available research information, rangeland feedstocks such as switchgrass appear to be ecologically sustainable biofuel feedstocks, particularly when they replace croplands. Managing switchgrass for Bioenergy is an energetically positive and environmentally sustainable production system throughout much of the central Great Plains and Midwest east of 100o West Longitude. Switchgrass is not a one-size-fits-all Bioenergy feedstock. However, it is the best available perennial herbaceous Bioenergy feedstock candidate for many agro-ecoregions, and has most of the desirable characteristics of an ecologically sustainable Bioenergy feedstock. We encourage further research on mixed species systems, particularly as a means to reduce exogenous N inputs, produce biomass for Bioenergy, as well as manage and maintain native prairie ecosystems.
Technical Abstract: Sustainable agro-ecosystems are those systems whose production does not negatively affect energy flow, nutrient cycling or ecosystem services. We examined literature reports in each of these different arenas to determine if cellulosic biomass production in rangelands met these criteria. We focused particularly on switchgrass (Panicum virgatum L.) and found that compared with multi-species systems and compared across a range of soil types and management protocols, the answer to the question of whether these arenas were negatively affected was mixed. However, when switchgrass was compared with annual row crops, the answer was resoundingly positive. We found that there were no standardized methods for life cycle assessment (LCA) or experimental protocols. Therefore, we suggest that long-term agricultural research sites be established across the agricultural ecoregions of North America and that these areas be subjected to standardized experimental, modeling and LCA protocols. Until common techniques are used, questions about the long-term sustainability of these agro-ecosystems will be difficult to answer unequivocally. However, based on currently-available research information, rangeland feedstocks such as switchgrass appear to be ecologically sustainable biofuel feedstocks, particularly when they replace croplands.