Cultivation of bioenergy crops is predicted to increase to between 27 and 120 million acres by 2022 in order to meet the renewable energy needs of the U.S. and the Environmental Protection Agency’s Renewable Fuel Standard. These crops may be used for production of ethanol, biodiesel or heat through combustion. Ideally, these renewable energy sources would neither compete with food production nor require land with high natural values or agricultural productivity. While early progress on meeting the Standard was based on corn and soybeans, there is increasing concern about the conversion of vast areas from food to fuel crop cultivation.
As a result, an entrepreneurial industry is emerging focused on identifying bioenergy crops that will help fill the gap. However, one risk associated with the species and genotypes under development is their potential, once planted over vast acreages across multiple environments, to become established pests beyond the cultivation site. The U.S. has multiple examples, from kudzu to hydrilla to tamarisk, of plant species intentionally introduced for agriculture, forage, erosion control or horticulture that have become invasive. These harmful invaders represent fewer than 10 percent of species that have moved beyond their native range, but their spread has impacted agricultural production, navigation and biodiversity. These species now require extensive, expensive — and often carbon-based — control efforts.
These harmful invaders share many characteristics with bioenergy crops: highly productive with little need for irrigation or fertilization over a broad range of environments, rapidly regrowing after harvest, and having few pests. While these benefits are valuable in a bioenergy crop, it is important to consider the potential invasiveness of these species to avoid the risk of creating one environmental problem as we attempt solve another.
To reduce the potential that a biofuel crop will become invasive, scientists are using risk assessment tools that can screen non-native plant species prior to investment in cultivation. These screening tools allow for commerce in valuable, non-invasive species, while excluding the species that cause damage. This preventative approach is well established in the U.S., where we have long-standing national and state regulatory policies to prevent impacts of non-native species to agricultural productivity, and more recently, natural areas. The current tools have been demonstrated to accurately distinguish more than 90 percent of harmful plant invaders from non-invaders.
My colleagues and I have used one such risk assessment tool to evaluate the potential invasiveness of 120 plants under consideration or cultivation as bioenergy feedstocks, published recently in BioEnergy Research. Our intent was to develop a list of species that have a low risk of becoming invasive and could be incentivized for research and cultivation. Conversely, we hope that species predicted to become harmful invaders would not be incentivized under federal or state policies. This preventative and proactive approach provides greater regulatory and financial predictability for both industry and agencies.
Of the 120 species, there were 24 species native to the U.S. identified as posing no invasion risk when cultivated within their native range. Examples of these species include honey locust, tulip poplar and switchgrass. More interestingly, more than 25 percent of the non-native species evaluated using the risk assessment tools were predicted to have low risk of becoming invasive. These species includes sugarcane, sweet sorghum, giant miscanthus (sterile cultivars), sugar beets and field mustard, along with corn and soybeans. Combined, there are 49 native and non-native species on the ‘white list’ for bioenergy crops.
As more species and cultivars are proposed to help meet the substantial renewable energy needs of our nation, more risk assessments will be necessary to identify the truly green renewable alternatives to petroleum-based energy sources. Our work demonstrates that these alternatives do exist, and we do not have to accept invasion risk as a trade-off for reducing risks associated with rising carbon dioxide levels.
Lead image: Bioenergy via Shutterstock