Federal policies limiting corn-derived biofuels have led to a rising interest in alternative energy crops. However, many novel energy crops are imports to the U.S. and may share key traits with invasive plants. In fact, some bioenergy feedstocks are already known to be aggressively invasive in different parts of the country.
Unfortunately, the EPA doesn’t appear to be taking the lead on containing them. For example, the EPA last year approved Arundo donax (giant reed) as a new fuel pathway, despite its well-established record as an invasive species. This large bamboo-like reed dominates riparian ecosystems (the land bank adjoining rivers and streams) throughout California, Texas, and other southern coastal states. What’s more, it can cost up to $25,000 per acre to control. Scientists have projected a high level of invasion risk for a number of leading energy crops, including A. donax, Pennisetum purpurem (napier grass, also approved by EPA), Jatropha curcas, fertile Miscanthus species, several Eucalyptus species, and more.
Yet, with all of the attention paid to these potential “bad actors”, few safe alternatives have been offered or publicized. From my conversations with members of the bioenergy industry, I know that such alternatives would be welcomed. With this in mind, my collaborators and I set out to create a list of low-risk feedstocks (a “white list”) that could be adopted by the energy industry and by legislators looking to incentivize the use of environmentally friendly crops. (You can read the full article, along with the complete white list, in BioEnergy Research.)
We started by compiling a list of crops being grown or considered for energy uses, at all stages of development from early research to crops widely grown and subsidized by the USDA. While we came up with a large list (120 taxa), we recognize that new crops are continually being developed and that our list should not be considered permanent or comprehensive. Once the initial list was complete, we determined which plants were native to the U.S. and placed those on our white list (see link for a simplified online white list).
The use of native species, which are pre-adapted to growing conditions in the U.S., can minimize the need for intensive agricultural inputs, support native fauna, and be less likely to overtake other natives if they escape from cultivation. However, it is important to note that “native to the U.S.” does not necessarily mean that a species is native to the entire U.S. In fact, there are examples of native plants that act invasive when transported across the country. Thus, we specifically recommend that the 24 native feedstocks on our white list be cultivated only in their native range. Take Panicum virgatum (switchgrass), which qualified for our white list. It is native to the majority of the continental U.S. except Washington, Oregon, and California. This means native varieties could be planted safely anywhere in the country other than those three states. Other white list natives include Agropogon gerardii (big bluestem), native Agave, Populus (poplar) and Salix (willow) species, as well as a number of Pinus (pine) species. It is also important to point out that “improved” genotypes of native species could feature invasive traits (e.g., more prolific seed production) and would need to be assessed separately for invasion risk.
For the remaining non-native species, we searched public databases and literature for the results of Weed Risk Assessments (WRAs). The WRA is a reliable (>90% accurate), science-based risk assessment tool that predicts the risk of invasion by imported plants in novel environments. It places plants into three categories: high risk, low risk, and “evaluate further”. Those that receive an “evaluate further” determination can often be placed into a more definitive category after applying a secondary screening process. Twenty five of the non-native plants in our feedstocks list were determined to be low risk, and were moved to the white list. Low-risk non-natives include sterile Miscanthus × giganteus hybrids, Sorghum bicolor ‘sweet’ (sweet sorghum), several Eucalyptus species, as well as already-proven first generation crops Zea mays (corn) and Glycine max (soybean).
Overall, this white list offers 49 native and low-risk non-native options that could be grown in a number of geographic regions in the U.S. and can be processed into a variety of energy products (e.g., ethanol, biodiesel, and combustible pellets). As previously mentioned, the list is a best estimation of currently available feedstocks using the best current information. As new feedstocks are developed or new information allows completion of weed risk assessments, the list will likely change over time.
In addition to being immediately useful for industry members looking to develop new products, the white list concept can be adopted by legislators and regulators as they develop rules for bioenergy plantations. An easy-to-use and science-based metric is needed to improve regulations at both the state and federal levels.
Currently, only four states include language relating to invasiveness in their renewable energy regulations. At the federal level, USDA’s Biomass Crop Assistance Program (BCAP) prohibits subsidies for invasive energy crops, but EPA’s new fuel pathway approval process currently includes no invasiveness assessment except in ad hoc cases like the Arundo donax example above. State and federal white lists could streamline the approval process, incentivize use of safer feedstock alternatives, and avoid costly and environmentally damaging mistakes made as the industry grows.