Study cautions on sole focus on energy crop biomass yield; perennial grasslands deliver greater ecosystems services than corn
A study by a team from the DOE’s Great Lakes Bioenergy Center has concluded that focusing on the yield of an energy crop alone can come at the expense of many other environmental benefits. The study, published as an open access paper in the Proceedings of the National Academy of Sciences (PNAS), found that switchgrass and prairie plantings harbored significantly greater plant, methanotrophic bacteria, arthropod, and bird diversity than corn.
Although the corn biomass yield was higher, all other ecosystem services, including methane consumption, pest suppression, pollination, and conservation of grassland birds, were higher in perennial grasslands.
Agriculture is being challenged to provide food, and increasingly fuel, for an expanding global population. Producing bioenergy crops on marginal lands—farmland suboptimal for food crops—could help meet energy goals while minimizing competition with food production. However, the ecological costs and benefits of growing bioenergy feedstocks—primarily annual grain crops—on marginal lands have been questioned. Here we show that perennial bioenergy crops provide an alternative to annual grains that increases biodiversity of multiple taxa and sustain a variety of ecosystem functions, promoting the creation of multifunctional agricultural landscapes.
…Moreover, we found that the linkage between biodiversity and ecosystem services is dependent not only on the choice of bio-energy crop but also on its location relative to other habitats, with local landscape context as important as crop choice in determining provision of some services. Our study suggests that bioenergy policy that supports coordinated land use can diversify agricultural landscapes and sustain multiple critical ecosystem services.—Werling et al.
The implication of the study is that careful design of bioenergy landscapes has the potential to enhance multiple services in food and energy crops, leading to important synergies that have not yet informed the ongoing bioenergy debate. This study is especially timely as high commodity prices are driving conversion of marginal lands to annual crop production, reducing future flexibility.
We believe our findings have major implications for bioenergy research and policy. Biomass yield is obviously a key goal, but it appears to come at the expense of many other environmental benefits that society may desire from rural landscapes.—Doug Landis, a biologist at Michigan State University (MSU) and corresponding author
Landis and a team of researchers from the Great Lakes Bioenergy Research Center and the National Science Foundation (NSF) Kellogg Biological Station Long-Term Ecological Research (LTER) site compared three potential biofuel crops: corn, switchgrass and mixes of native prairie grasses and flowering plants. (Kellogg Biological Station is one of 26 such NSF LTER sites in ecosystems from grasslands to coral reefs, deserts to mountains around the world.)
The scientists measured the diversity of plants, pests and beneficial insects, birds and microbes that consume methane. Methane consumption, pest suppression, pollination and bird populations were higher in perennial grasslands.
In addition, the team found that the grass crops’ ability to harbor such increased biodiversity is strongly linked to the fields’ location relative to other habitats.
For example, pest suppression, which is already higher in perennial grass crops, increased by an additional 30% when fields were located near other perennial grass habitats.
That suggests that to enhance pest suppression and other critical ecosystem services, coordinated land use should play a key role in agricultural policy and planning, Landis said. However, rising corn and other commodity prices tempt farmers to till and plant as much of their available land as possible.
Corn prices are currently attractive to farmers, but with the exception of biomass yield, all other services were greater in the perennial grass crops. If high commodity prices continue to drive conversion of these marginal lands to annual crop production, it will reduce the flexibility we have in the future to promote other critical services like pollination, pest suppression and reduction of greenhouse gases.—Doug Landis
Scientists from the University of Wisconsin, University of Nebraska, Bard College and Trinity Christian College were part of the research. The work was also funded by the US Department of Energy and MSU AgBioResearch.
Ben P. Werling, Timothy L. Dickson, Rufus Isaacs, Hannah Gaines, Claudio Gratton, Katherine L. Gross, Heidi Liere, Carolyn M. Malmstrom, Timothy D. Meehan, Leilei Ruan, Bruce A. Robertson, G. Philip Robertson, Thomas M. Schmidt, Abbie C. Schrotenboer, Tracy K. Teal, Julianna K. Wilson, and Douglas A. Landis (2014) “Perennial grasslands enhance biodiversity and multiple ecosystem services in bioenergy landscapes,” PNAS doi: 10.1073/pnas.1309492111