Wheatgrass may be a sneaky invader
Copyright 1999, Environmental News Network
November 7, 1999
By Margot Higgins
Unlike other invasive species, such as zebra mussels that have been accidentally introduced into U.S. ecosystems, crested wheatgrass was deliberately planted throughout the Great Plains and western United States for more than 50 years.
Although the grass has extracted soil from native grasses on much of the northern Great Plains, its conquest until now has seemed relatively harmless to the larger environment.
But co-author of the study, Scott Wilson from the University of Regina in Canada warns, "the damage may not be as obvious (as the damage caused by zebra mussels and other invasive species) because sometimes it takes over 200 years for an invader to become invasive."
Crested wheatgrass was originally brought to the Americas from Siberia during the drought-filled years of the Great Depression, when farms in the "Dust Bowl" were failing and the local prairie grass did not provide a sufficient diet for cattle. Farmers discovered that the wheatgrass was hardy, produced good hay, resisted drought and overgrazing and had a long growing season.
The introduction was so successful that ranchers and government agencies continue to spread it enthusiastically from the Great Basin to the Northern Plains. Today crested wheatgrass blankets 25 million acres of prairie in North America.
According to Wilson, crested wheatgrass is causing far more harm than good.
He and co-author Janice Christian compared hundreds of samples of grass and soil from Canada's Grasslands National Park in southwestern Saskatchewan, which hosts both crested wheatgrass and native grass.
After analyzing their samples, the scientists found that the soil beneath crested wheatgrass contained significantly less nutrients and organic matter than the soil under native prairie.
To explain this, Christian and Wilson point to the different growth strategies of the two grasses.
Wheatgrass devotes most of its energy to producing aboveground shoots, while maintaining only a meager root system. Conversely, the native grasses do not grow as tall, but instead develop an extensive network of roots. Previous studies have shown that roots play a more important role than do shoots in enriching the ground with nutrients and organic matter.
Another significant implication of the study is that the conversion of native prairie to wheatgrass may have eliminated an important storage area for atmospheric carbon. The researchers reason that if native prairie grasses put more nutrients into the soil and plant tissue, they are effectively tying up carbon that would otherwise be in the atmosphere, in the form of a greenhouse gas.
"Our results suggest that soils re-vegetated with native grasses would be a much more effective sink for carbon," says Wilson. He and Christian calculate that in the long run, the introduction of wheatgrass may have left 480 million tons of carbon in the atmosphere, which could have been stored beneath rich native prairie. This atmospheric carbon might be contributing to the greenhouse effect.
To put the figure in perspective, 480 million tons is approximately the same as the amount of fossil fuel burning conducted by the entire globe in one month. And crested wheatgrass is only one species; no one has confirmed yet how other introduced species might contribute.