ISSUES IN ECOLOGY NUMBER SEVENTEEN SPRING 2013 ples for biofuels and sustainability to a land- and whether the feedstock crop replaces Potential Environmental 4))the e of nirogen Effects ential environmental effects of biofu els production have been examined using field native rainforest).Whether biofuels produc. net GHG emis ereatly depending on ini nosphere (e carbon in ndson the entire life cycle For this r nhouse Gas Emissions and Soil of production Carbo sments), nown as cribe Terms and Definitions biofuels Liquid fuels derived from biological materials such as crop plants.forest products.or waste materials carbon deb has lower greenhouse gas emissions than the fossil fuel that it replaces (see reference 8). cellulosic Refers to fuel derived from vegetative plant tissue,composed primarily of cellulose,hemicellulose,and g3eegopesdeswod.andgnsnothanetediorgancontatiogan-basodo CO, Carbon dioxide CRP Conservation Reserve Program of the U.S.Department of Agriculture EPA United States Environmental EU European Union fe dstock The materia or biofuel,for example,age,cop plants,waste materials,orwood foregone sequestration 地tdeppgoudohenwehaebensoedbyam6scogennthaeneosconesontn GHG Greenhouse gas hypoxia Oxygen deficiency indirect land use change o-til Famming without plowing (llage);the prior crop's residue is left on the soil surface to decompose. no Nitrous oxide RFS stover Comn leaves and stalks.a potential cellulosic feedstock USDA United States Department of Agriculture 4 esa The Ecological Society of America esahq@esa.org ISSUES IN ECOLOGY NUMBER SEVENTEEN SPRING 2013 ples for biofuels and sustainability to a land￾scape approach designed to meet social, eco￾nomic, and energy needs. Potential Environmental Effects The potential environmental effects of biofu￾els production have been examined using field measurements, laboratory experiments, com￾puter models, and combinations of two or more of these methods. Not all studies agree with each other, and we discuss some of the reasons for differing conclusions. The effects of biofuels on the environment are many and complex; they vary greatly depending on ini￾tial conditions and assumptions. Greenhouse Gas Emissions and Soil Carbon GHG emissions resulting from biofuel produc￾tion depend on 1) land clearing, if necessary, and whether the feedstock crop replaces native vegetation or another existing crop; 2) feedstock choice; 3) fuel and energy use for crop growth, harvest, and biofuels production; 4) water use and source; 5) the use of nitrogen fertilizers; and 6) soil turnover effects on car￾bon and nitrogen emissions (Box 3). The use of fossil fuels and nitrogen fertilizer has direct effects on emissions. Indirect effects can occur when biofuels production displaces another agricultural activity (e.g., cattle grazing in tropical regions which then expands into native rainforest). Whether biofuels produc￾tion causes net GHG emissions, has no net GHG emissions, or takes up GHGs from the atmosphere (e.g., by storing carbon in plant roots and soil) depends on the entire life cycle of production and use. For this reason, researchers studying the effects of biofuels pro￾duction on GHG emissions generally conduct life cycle analyses (or assessments), known as LCAs (Box 4). An LCA describes the impacts of a product at every step from start to finish— 4 esa © The Ecological Society of America • esahq@esa.org Terms and Definitions biofuels Liquid fuels derived from biological materials such as crop plants, forest products, or waste materials carbon debt The amount of carbon released as a result of land use conversion, for example from grassland or forest to crops for biofuels production. The carbon debt can be repaid over time if the biofuel produced has lower greenhouse gas emissions than the fossil fuel that it replaces (see reference 8). cellulosic Refers to fuel derived from vegetative plant tissue, composed primarily of cellulose, hemicellulose, and lignin (for example, crop residues, wood, and grass not harvested for grain); contrast to grain-based or algae-based biofuels. CO2 Carbon dioxide CRP Conservation Reserve Program of the U.S. Department of Agriculture EPA United States Environmental Protection Agency EU European Union feedstock The source material for biofuel, for example, algae, crop plants, waste materials, or wood foregone sequestration The carbon that would otherwise have been stored by an ecosystem in the absence of its conversion to biofuel cropping GHG Greenhouse gas hypoxia Oxygen deficiency indirect land use change Refers to the carbon cost of converting grassland or forest to food crops in order to replace the food production lost when cropland elsewhere is diverted to biofuels production no-till Farming without plowing (tillage); the prior crop’s residue is left on the soil surface to decompose. N2O Nitrous oxide RFS Renewable fuel standard. The first RFS was established by the U.S. Environmental Protection Agency under the Energy Policy Act of 2005. RFS2, an expanded version of the standard, was developed in response to the Energy Independence and Security Act of 2007. stover Corn leaves and stalks, a potential cellulosic feedstock USDA United States Department of Agriculture