Read this interesting article.
Eryn Gable, special to Land Letter
CHEYENNE, Wyo. — Researchers here are studying how climate change will affect semiarid grassland ecosystems in the West over the next 50 years, information they say is critical for developing management options to address the effects on Western rangelands.
The Prairie Heating and CO2 Enrichment (PHACE) experiment includes research on how elevated carbon dioxide and global warming will affect nutrient and water dynamics, plant production, species change, weed invasion and forage quality. Armed with this information, the researchers hope their work will help ranchers and land managers deal with the anticipated increased variation in weather and develop management practices to account for altered productivity and declining forage quality due to global change.
|Jack Morgan explains the treatments. Photo by Eryn Gable.
“This is research I think that society is telling us is important — that has potentially large impacts on policy as well as on management,” said Jack Morgan, a plant physiologist with the Agricultural Research Service who is heading up the project.
Steve Gray, Wyoming’s state climatologist, noted that Wyoming and the West are extremely vulnerable to climate change because it is expected to make an already dry climate even drier. For example, 71 percent of Wyoming receives less than 16 inches of precipitation annually, making it the fifth-driest state in the country.
“We’re so dry to begin with that any change in the amount of moisture that we have, up or down, is going to have dramatic impacts on ecosystems in this part of the world,” Gray said.
One of the big questions in climate change science right now is what will happen with elevated CO2, with some scientists predicting that the increase in carbon dioxide levels will swell plant production, allowing more carbon to be sequestered in the system.
“The hope would be that eventually these systems will help assimilate and remove more carbon from the atmosphere,” Morgan said. “It turns out that things aren’t nearly that simple, and it’s an open question right know what the long-term response to carbon in the system will be with elevated CO2.”
The experimental site
The PHACE experiment is at a 6-acre site on the Agricultural Research Service’s High Plains Grasslands Research Station, located about 10 miles west of Cheyenne. It is currently scheduled to run five years, ending in 2010, when the first results are expected.
|One of 30 circular plots, with a variety of CO2, irrigation and temperature treatments, that are part of the Prairie Heating and CO2 Enrichment (PHACE) experiment at the Agricultural Research Service’s High Plains Grasslands Research Station. Photo by Eryn Gable.
It is composed of 30 circular plots, with a variety of CO2, irrigation and temperature treatments. “In the end, CO2, temperature and precipitation all affect water, and we think that’s going to be the main driver of how the rangelands respond to climate change,” Morgan said.
The temperature changes are controled by six 1,000-watt heaters attached to a heater array, making the sites 1.5 degrees Celsius warmer during the daytime and 3 degrees Celsius warmer at night. The heaters use as much power as about five to six residential homes.
The project uses liquid CO2, stored in a 100,000-gallon refrigerated tank, which is then delivered through a ring around the plots and is maintained at a level of about 600 parts per million. Carbon dioxide levels presently stand at 385 ppm, about 38 percent higher than pre-industrial levels, according to the National Oceanic and Atmospheric Administration. The Intergovernmental Panel on Climate Change projects that atmospheric carbon dioxide levels could reach 450 to 550 ppm by 2050.
The project uses about 1 ton of CO2 daily, at a price of $80 a ton. A total of about 6 miles of tubing, wire and cable is used in the project. Morgan estimated that the project costs at least $300,000 a year.
The scientists are also looking at irrigation, because elevated CO2 levels are expected to lead to the closure of plants’ stomata, causing them to withdraw water from the soil more slowly and letting water content build up in the soil over time. The researchers have designed “shallow” irrigation treatments, in which water is applied six to seven times during the March-October growing season under ambient CO2 conditions, to match the water content of the soil occurring in plots with elevated CO2 levels. This should allow them to determine whether water replacement gives the same response as elevated CO2. The researchers are also using “deep” irrigation treatments, which apply the same amount of water in two irrigation events, rather than six to seven, under ambient CO2 conditions.
“We’re trying to characterize a number of different ecosystem attributes that we think are important that will tell us how this ecosystem is going to respond in the future and also will tell us what role this ecosystem plays in the carbon and trace gas cycle,” Morgan said. “Is it a sink for these gases? Is it a source? Can it be part of the solution by changing management practices?”
Morgan acknowledges that there are limits to this type of research, however. “They are not considered simulations of the future, because we don’t know exactly what combinations of temperature and CO2 we’re facing, so we have to take this information, put it into models and sort of come up with our final guesses as to how the future is going to unfold for rangelands,” he said.
For example, Morgan noted that the research plots receive an instantaneous doubling of CO2 levels, whereas CO2 is actually increasing gradually over time in the atmosphere, as is temperature. The sudden influx of CO2 represents a shock to the system, and scientists have to try to take that into account when interpreting their data, he said.
The PHACE experiment builds on previous research that has examined some of the effects of climate change on grassland ecosystems, often looking at individual variables such as elevated carbon dioxide levels or changes in the size and timing of rainfall. For example, in an experiment at the Central Plains Experimental Range near Nunn, Colo., scientists found that doubling the CO2 levels consistently increased plant production, but that cool-season grasses performed better than warm-season grasses and forage quality lessened. In a rainfall manipulation experiment, scientists found that a shift from 12 to four rain events resulted in an increase in productivity in semiarid grasslands in Colorado, even though the overall amount of precipitation remained steady.
Impact to grasses
The PHACE experiment is unique because it looks at the interaction between CO2 and temperature. So far, the preliminary results of the study, based on one year’s worth of data, show increases in plant production as high as 20 percent, with blue gramma, a warm-season grass, seeming to respond best to elevated CO2 and warmer temperatures.
|Previous experiments have shown the dalmatian toadflax, an invasive species, responds positively to elevated CO2 levels, but not warming temperatures. So far, though, the plants appear to be doing almost as well with high CO2 levels and warming as in the plots with high CO2 alone. Photo by Eryn Gable.
If that trend continues, Morgan said, the significance will depend on how much of a competitive advantage it provides and what species are the losers. “If some plants increase, it may be at the expense of other species. It’s a little early to tell what those other species are gonna be,” Morgan said. “I think it’s an indication that grasslands will respond and are responding to climate change.”
If a grassland consists of mostly warm-season grasses, then there will be certain times of year when more of that forage will be available, Morgan said. Grazing itself tends to reduce the amount of cool-season grasses on a landscape.
“We’re interested in finding management practices that can keep cool-season grasses in,” he said. “It extends the grazing season. … If climate change is going to push us toward more warm-season grasses, I think we’re going to have to understand that and just keep it in mind, so that when we manage these grasslands, we can find a way to encourage cool-season grasses.”
Researchers are also keeping a close eye on invasive species, since many of these plants seem to thrive in conditions with elevated CO2.
“The big question is, what’s going to come in next, and one concern is that what’s going to come in next is an invasive species of some kind,” said Dana Blumenthal, an ecologist with the Agricultural Research Service.
So far, those concerns appear to be justified, since the dalmatian toadflax, a yellow-flowered plant native to Europe and Asia, is doing almost as well in the test plots with higher temperatures and elevated CO2 as those with elevated CO2 alone. “It’s the worst invader we have in this part of the mixed-grass prairie,” Blumenthal said.
Another concern is that under higher CO2 concentrations, plants appear to building less protein, potentially lowering their forage quality, said David Williams, an associate professor at the University of Wyoming. While the plants are increasing their productivity, resulting in 20 percent increases in biomass, the nitrogen levels in the plants are decreasing by 30 percent, he said.
Gable is an independent energy and environmental writer in Woodland Park, Colo.