Scientists searching for the next big energy-producing biofuel, something such as switchgrass that power plants could burn to make electricity and reduce their carbon emissions, have a very fussy wish list.
Ideal species should not be food crops. They need to grow quickly and have to be successful on marginal land that's less suited to growing food crops. They should be resistant to disease and pests, and also produce enough biomass to make them competitive with fossil fuels.
The problem is that plants with good possibilities often have the same traits that make them potentially invasive species, said Lauren Quinn, an invasive plant ecologist at the University of Illinois' Energy Biosciences Institute. That prompted Quinn and her colleagues to come up with a white list of potential species that were appropriate for biofuel use and had low risk of becoming invasive. The research appeared last month in the journal BioEnergy Research.
Quinn said most previous studies on potential biofuel plants, or feedstocks, focused on identifying highly invasive ones that should be avoided if possible.
"We don't really hear the good news of the feedstocks, so the industry is left wondering what to do," she said.
To come up with a final list, the researchers tracked the invasiveness potential of 120 possible species with a tool called the Australian weed risk assessment model. The tool evaluates characteristics like reproductive traits, tolerance for different climates, genetic makeup and competition with other species. Plants that score low on the assessment are considered to be non-invasive, while those that score high are high invasive.
The researchers narrowed down the candidates to 49 native and nonnative plants that all had low invasive risk. Some potential candidates included soybeans, some varieties of eucalyptus, switchgrass and poplar.
Of the final 49 species, 24 of them were native plants. The researchers suggested these species could only be safely used as biofuels within their current ranges. That left 25 types of plants with wide-ranging potential as biofuels, said Doria Gordon, the director of conservation science at the University of Florida.
Would a noxious weed, by another name, work?
"We're not saying don't make biofuels, we're saying let's be careful, and let's look at these 25 [species] first," Gordon said.
The study did not consider other features of the white-listed species such as water use or susceptibility of pests and disease, factors that are also important for potential feedstock.
For Gordon and the other researchers, the cost of eradicating invasive species outweighs the downsides of less efficient plants. "Even if [these species] aren't as productive, we have a lot to work with," Gordon said.
Some of these plants could be selectively bred to produce more sugar, or higher fiber, she added.
Still, invasive plants like Arundo donax, remain attractive within the energy industry because of the sheer volume of biomass they are able to produce in a short period of time. The giant reed can grow about 30 feet in a year, has few pests and can grow in less nutrient-rich soil. It is also considered a noxious weed in Texas and highly invasive in California.
In Oregon, Portland General Electric (PGE) is looking at ways to convert its coal-burning Boardman plant to using biomass by 2020. PGE is growing a test plot of the giant reed, said PGE spokesman, Steve Corson.
The company is aware of the invasive nature of the plant, and they are working with state and county government to implement effective weed controls as part of the testing process, he said.
"One of the attractive things about Arundo is its properties are pretty similar to corn and alfalfa," Corson said. "We're going to need a lot of biomass, so there is a lot of appeal to looking at a dedicated plant."
PGE is also considering other alternatives like using forest and agricultural waste, or sorghum. The power plant is planning a test burn next year, possibly in the spring. "From our research so far, it seems like an area worth pursuing," Corson said.
In Florida, buy a permit and post a bond
Some members of the biofuel industry are already exploring some less invasive crop options. REPREVE Renewables LLC produces modified rhizomes of Miscanthus x giganteus, a sterile hybrid type of perennial grass, for use as a feedstock.
The company works closely with farmers, even helping to plant and harvest the crop to ensure the species does not become invasive. Growers use buffer zones around the field as one method of keeping it there, said Jeff Klingenberg, the vice president of R&D operations at REPREVE.
Although biofuel production using alternative plant sources is still developing, Klingenberg is cautiously optimistic. "I think the marketplace is going to grow over the next several years," he said.
Not only do Quinn and her colleagues want to see more industry adoption of low-invasive feedstock plants, they also want state and federal governments to step up regulations and communicate more clearly between agencies.
Florida is one state that has developed a comprehensive plan for managing feedstock cultivation.
Growers interested in planting in the state have to pay a $50 fee and apply for a permit to cultivate anything over more than 2 acres of land. The permit includes detailed questions about the species, and potential growers have to develop a plan and budget for eradication, should the plant turn out to be harmful. They have to send in a sample of the plant, that is then positively identified by scientists at the University of Florida, who work in partnership with the state to combat invasive species.
If the plant is identified as a possible problem, state officials will work with the grower to further develop management strategies, said Trevor Smith, the bureau chief of the Florida Department of Agriculture, Division of Plant Industry.
In addition to the permit, growers also have to buy a surety bond worth 150 percent of the anticipated cost of eradicating the plant. The grower pays about $200 per year, and the bond acts like insurance for the state, Smith said. The state can cash in the bond to pay for eradicating the plants if the grower decides to suddenly abandon production.
"Overall, the thrust of the rule is right," Smith said. "It's a nice balance to keep us safe and not scare away growers. We really think Florida could be a leader in biofuels, but we want to do this safely."
Two rules for a giant reed
According to Smith, a number of other states including Idaho and Mississippi had asked for information about their model in hopes of replicating Florida's approach.
Quinn said that the one flaw with Florida's system was that the cost of the bond was too conservative and would not be enough to fully eradicate an invasive plant.
Coordination at the federal level can be more complicated because of the breadth of agencies involved.
The researchers note in the study the seemingly contradictory policies for Arundo donax within the federal government. While the USDA Plant Epidemiology and Risk Analysis Laboratory lists the giant reed as highly invasive, it was approved for cultivation under the renewable fuel standard (RFS), administered by U.S. EPA.
In a statement, EPA spokeswoman Enesta Jones said, "The EPA coordinates with USDA on an ongoing basis regarding the review and approval of new feedstocks under the RFS program."
Potentially invasive species like Arundo donax have to go through additional regulatory requirements in order for the plant to be registered as a possible renewable fuel source. Producers also have to submit a letter from USDA to EPA that states whether there is "a significant likelihood of spread beyond the planting area of the feedstock," according to Jones.
"This is really the EPA trying to reduce potential for harm while still meeting the mandate for increasing renewable fuels," said Chris Dionigi, the deputy executive director of the National Invasive Species Council, an interagency coordinating body.
As to whether growers may be willing to use species from Quinn's white list as a way to reduce the risk of spreading invasive species, Dionigi said, "A consistent theme is you are almost always more successful if you give people an alternative."
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