OPEI seeks correction and public disclosure of significant computation error in turfgrass report

The Outdoor Power Equipment Institute (OPEI) announced Feb. 15 that Dr. Amy Townsend-Small of University of California-Irvine (UC-Irvine) acknowledged a computation error of carbon used to maintain turf in the Jan. 19 released UC-Irvine study titled “Carbon Sequestration and Greenhouse Gas Emissions in Urban Turf.” With the error corrected, ornamental grass is in fact shown to be a net sequester of carbon even when inputs are accounted for in grass maintenance. The correction has been submitted to the American Geophysical Union (AGU), which published the paper. 

Upon review of the report, various flaws were discovered, including one significant math error that was made in computing the carbon consumed during mowing. The carbon from fuel consumption was multiplied by 12, one too many times, to convert from monthly to annual data. The error was not caught during the peer review process prior to publication of the paper by the AGU. When the computation is corrected, turfgrass actually is a net sequesterer of carbon dioxide, reversing the conclusions of the original report that was widely reported in the media.

“Blaming grass for contributing to global warming is a non-starter when you look at the facts,” said Kris Kiser, executive vice president of OPEI. “The grass in your backyard is working hard to keep us cool, soak up carbon, capture particulates, produce oxygen, capture rain water, and reduce run-off. We need to focus on the right plant in the right place and on management practices that maximize the environmental benefits potential of turfgrass.”

Kiser added, “While the UC-Irvine study, rightly so, highlights that mismanagement of turfgrass can occur via excessive fertilization and irrigation, and inefficient maintenance practices, the focus should be on proper management techniques.” OPEI stressed that proper management techniques can minimize carbon emissions and maximize the benefits of carbon sequestration in turfgrass — for example, proper selection of turf based on climatic region (drought-resistant species) and leaving grass clippings on the grass to serve as a natural nitrogen fertilizer.

OPEI also noted that the UC-Irvine study did not acknowledge the dramatic reductions of emissions and fuel use profile for today’s gasoline and diesel equipment, nor did the study disclose what model equipment and corresponding fuel use numbers were used. 

Mowers and outdoor power equipment today are the cleanest in history and fully regulated by the U.S. Environmental Protection Agency (EPA) and California’s Air Resources Board (CARB) since 1997. EPA Phase 3- and CARB Tier 3-compliant product are 90 percent cleaner than pre-1997 models. Coupled with improvements in emissions, there have been substantial improvements in mower fuel efficiency. Additionally, outdoor power equipment manufacturers have introduced a number of electric, battery, biodiesel, gasoline-electric and diesel-electric hybrids, propane, CNG, solar and other alternative fueled products with corresponding reductions in carbon output.

Other issues found with the UC-Irvine urban turf study include the following: 

The paper uses a technique (passive flux chambers) that is often inaccurate in measuring surface flux because it is not clear that what is being measured is at equilibrium. 
The UC-Irvine study focused on one urban center in southern California. Management techniques across the country are variable and therefore, can’t be applied broadly. Future studies should look at sites in other parts of the country. 
The UC-Irvine study did not measure actual inputs of water and nutrition but made estimates based upon standards or agriculture averages. Future studies should measure actual inputs or use the best available technology to estimate inputs of water and fertilization.

To learn more about the carbon sequestration benefits of turfgrass, see the paper titled “Technical Assessment of the Carbon Sequestration Potential of Managed Turfgrass in the United States” by Dr. Ron Sahu on OPEI’s Web site at www.opei.org.

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