Higher CO{-2} May Imperil Grasslands
Scientists warn of dire consequences for grazing areas
Rising levels of carbon dioxide in the atmosphere might be contributing to the conversion of the world’s grasslands - critical for livestock grazing - into a landscape of useless woody shrubs, according to a study released Monday.
By artificially doubling carbon dioxide levels over enclosed sections of the Colorado prairie, researchers created a dramatic rise in Artemisia frigida, commonly known as fringed sage. 
The study paints a harsh picture of what grazing lands could look like in 2100, when some estimates project carbon dioxide levels will be double today’s.
“To the extent that CO{-2} is driving this conversion, this suggests the problem is going to become more intractable in the future,” said Jack Morgan, a plant physiologist at the U.S. Department of Agriculture and lead author of the study, published in the Proceedings of the National Academy of Sciences.
Scientists say they believe the degradation of range lands, which cover about 40 percent of Earth’s land surface, is mostly the result of overgrazing and the modern practice of putting out fires rather than letting them burn, which destroys woody vegetation.
But researchers have long suspected that rising carbon dioxide levels also play a role.
Since at least the dawn of the Industrial Revolution, when carbon dioxide levels began to rise with the burning of fossil fuels, large swaths of the world’s seasonal grasses favored by livestock have been replaced by woody shrubs.
The concentration of carbon dioxide has risen from 280 parts per million at the end of the 18th century to 385 parts per million today.
To test the effects of the greenhouse gas, scientists set up open-topped cylinders of clear plastic, 15 feet in diameter, on a prairie 40 miles northeast of Fort Collins, Colo.
They pumped pure carbon dioxide into one group of cylinders, maintaining a concentration of 720 parts per million. The level in another group of cylinders was left at atmospheric concentrations and used as a control.
Each plot was analyzed every July, the end of the peak growing season. Then half the vegetation was removed to simulate grazing.
After five years, the researchers found a fortyfold increase in the biomass of fringed sage, from 0.72 of a gram per square meter in the first year to 28.7 grams per square meter in the fifth year. The area it covered increased from 0.2 percent to 4.1 percent.
The trend suggested that, given time, the sage eventually could squeeze out the grasses, Morgan said.
Woody shrubs have the ability to use carbon dioxide more efficiently than many grass species and have deeper roots than grasses, allowing them to tap into deeper water supplies.
Still, some scientists said carbon dioxide concentrations were likely to play a smaller role compared to overgrazing and fire suppression.
“The ranchers, through their own practices, have a stronger influence on the landscape than CO{-2} is likely to have, at least in the foreseeable future,” said Jeffrey Dukes, a biologist at the University of Massachusetts Boston who was not involved in the study.
Copyright 2007 Los Angeles Times
It’s a commonplace among folks concerned with pasture management that an appropriate level of grazing (for woody shrubs, particularly grazing by cattle, sheep, goats) is helpful in keeping the grass healthy. I question the effectiveness of simulating grazing by removing vegetation in July, at the end of the peak growing season. The most important time to graze down shrubs (and the time of year when livestock are most attracted to them) is in the spring, when the new shoots are prevalent and tender. Increased CO2 levels may create a vicious cycle here (as in other aspects of the environment), but I suspect that grazing patterns have more influence.
this is a non-issue, huge amounts of grassland are the result of human intervention in the first place. I think it’s pretty certain that native peoples living in the great plains of the world have been burning and expanding these areas for thousands of years. The article even mentions that burning of praries eliminated shrubs and inhibits their encroachment. And I thought global warming was going to increse the incidence of wildfires as well.
Add in the acidification of the CO2 saturated oceans and that’s effect on plankton, coral formation and crustaceans (thinning and pitted shells). Effects on all plants sensitive to CO2 changes favoring some over others in a formerly balanced environment as well as temperature changes and increased aridity.
A non-issue? I guess you could see it that way if you really wanted to?
Mucking up acidity can affect the balance of lignin vs cellulose in a plant - too much of the former and becomes less palatable.
There do exist, however, perennial forage plants that can be used as fodder such as tagasaste (Chamaecytisus palmensis), Acacia saligna and Flemingia macrophylla (to name but three). The hard part is that herders need to be trained in the propagation and usage of these plants.
“useless, woody shrubs”
Only useless if you believe the purpose of all life is to serve human wants. I think a change in perception is our only hope of survival. Technical marvels are not going to save us. We have to stop evaluating the world around us, stop seeing things as bad or good, based on how it affects our ability to exploit the rest of the lives with which we co-exist.
This study sounds a little flawed. The model for grazing doesn’t seem useful. The effects of increased CO2 are sure to be complex with increased groth of some species and increased wildfires, drought, torrential rains etc. I think this effect may be small…
Well lets hope that the increase of CO2 will give us some benefit. As for the rest…
Woody (headed) shrubs are the axis of evil!
Well if these predictions are right, You can bet Mother Earth will do something. We most likely will not like that something.
You know it makes me wonder how man never seems to learn from his mistakes.
It’s like mankind has a suicide wish. Well pretty soon that wish will be granted to a huge part of man’s population