Abstract
Perennial cellulosic feedstocks may have potential to reduce life-cycle greenhouse gas (GHG) emissions by offsetting fossil fuels. However, this potential depends on meeting a number of important criteria involving land cover change, including avoiding displacement of agricultural production, not reducing uncultivated natural lands that provide biodiversity habitat and other valued ecosystem services, and avoiding the carbon debt (the amount of time needed to repay the initial carbon loss) that accompanies displacing natural lands. It is unclear whether recent agricultural expansion in the United States competes with lands potentially suited for bioenergy feedstocks. Here, we evaluate how recent land cover change (2008–2013) has affected the availability of lands potentially suited for bioenergy feedstock production in the U.S. Lake States (Minnesota, Wisconsin, Michigan) and its impact on other natural ecosystems. The region is potentially well suited for a diversity of bioenergy production systems, both grasses and woody biomass, due to the widespread forest economy in the north and agricultural economy in the south. Based on remotely-sensed data, our results show that between 2008 and 2013, 836,000 ha of non-agricultural open lands were already converted to agricultural uses in the Lake States, a loss of nearly 37%. The greatest relative changes occurred in the southern half that includes some of the most diverse cultivable lands in the country. We use transition diagrams to reveal gross changes that can be obscured if only net change is considered. Our results indicate that expansion of row crops (corn, soybean) was responsible for the majority of open land loss. Even if recently lost open lands were brought into perennial feedstock production, there would a substantial carbon debt. This reduction in open land availability for biomass production is closing the window of opportunity to establish a sustainable cellulosic feedstock economy in the Lake States as mandated by current Federal policy, incurring a substantial GHG debt, and displacing a range of other natural ecosystems and their services.
Highlights
Bioenergy derived from perennial cellulosic energy crops, including woody biomass, may have the potential to reduce life-cycle greenhouse gas (GHG) emissions while providing better wildlife habitat and a range of ecosystem services that are not present, and often diminished, in today’s corn-grain ethanol production systems [1,2,3,4,5,6,7,8,9]
In order to understand the temporal dynamics of open land loss, we examined the area of open lands being converted to other land covers each year
The U.S is currently in a time of massive agricultural expansion, which competes with lands potentially suited for bioenergy feedstocks and affects the ecosystem services provisioned by the native ecosystems
Summary
Bioenergy derived from perennial cellulosic energy crops, including woody biomass, may have the potential to reduce life-cycle GHG emissions while providing better wildlife habitat and a range of ecosystem services that are not present, and often diminished, in today’s corn-grain ethanol production systems [1,2,3,4,5,6,7,8,9]. Lands that are low in carbon and nitrogen are generally not optimal for agriculture are often called ‘marginal lands’, and have been widely targeted in recent years as the most sustainable locations for the establishment of perennial cellulosic energy crops [18,19,20,21], often due to the assumed lack of competition with agriculture [22,23]. These ecosystems are marginal for agriculture, they have other existing values, including habitat, watershed protection and sequestered carbon. Converting these to bioenergy production can have a net benefit to habitat and other ecosystem services if they replace degraded lands that have less valued habitats or existing agriculture
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