Agricultural land dedicated to bioenergy crops is expanding rapidly (1), with multiple consequences for global climate, ecosystems, and food security. These consequences are closely tied to the land that is used for bioenergy crops. Using food agriculture lands for bioenergy agriculture could increase the cost of the food commodities that are critical to the diets of food-insecure people worldwide. Clearing forest land for new bioenergy crops could result in CO2
emissions from terrestrial carbon pools that aremuchgreater than any greenhouse gas benefits provided by biofuels. Raising bioenergy crops on agriculturally degraded and abandoned lands is emerging as a sustainable approach to bioenergy that provides environmental benefits and climate change mitigation without creating food-fuel competition for land or releasing the carbon stored in forests. These lands have been defined as areas that have been abandoned to crop and pasture due to the relocation of agriculture and due to degradation from intensive use. Growing conventional crops on these lands as a bioenergy feedstock could increase rates of erosion and polluted runoff, while field studies suggest that growing low-input, perennial grasses as a feedstock would likely reduce such impacts. Assessing the global potential of bioenergy production from agriculturally degraded and abandoned lands is challenging because of the high uncertainty associated with the spatial extent of these lands and the potential plant production on these lands. Existing assessments have provided only rough global estimates of the potential bioenergy from these lands, using estimates of the global area that are ultimately based on expert opinion, the assumption of a homogeneous spatial distribution, and spatially invariant or highly aggregated estimates of plant production. Such estimates range from 430 to 580 Mha of abandoned agriculture land, with mean global plant production on these lands of 1-10 tons aboveground biomass (AGB) ha-1 yr-1, meeting 2-23% of current global primary energy demand. In previous work, we developed a new method for estimating the abandoned areas that relies on historical land use data and found that the potential biomass production has an energy content of ∼5% of primary energy demand. Application of our data-driven approach at the national level could help inform policy makers of the potential scale of this bioenergy resource. Here we present a new global, spatially explicit estimate of abandoned agriculture and the associated plant production on these lands, using historical land use data, satellite-derived land cover, and global ecosystem modeling. We considered abandoned agriculture as land that was previously used for crop or pasture but has since been abandoned (and has not been converted to forest or urban areas). The spatially resolved biomass production is then combined with national-level energy use data to determine the potential contributions of bioenergy.

By: E. Campbell, D.B. Lobell, R. C. Genova, C.Field

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