Burning on the Prairies

Bhattacharya, A., Pacific Northwest National Laboratory

Radiation Processes

Cloud-Aerosol-Precipitation Interactions

Fischer ML, MS Torn, DP Billesbach, G Doyle, B Northup, and SC Biraud. 2012. "Carbon, water, and heat flux responses to experimental burning and drought in a tallgrass prairie." Agricultural and Forest Meteorology, 166-167, 10.1016/j.agrformet.2012.07.011.

Pasture burning during the beginning of the experiment at the USDA Grazing Lands Research Laboratory in March 2005.

Pasture burning during the beginning of the experiment at the USDA Grazing Lands Research Laboratory in March 2005.

What does it mean for the carbon cycle?

The deep drought in the United States that fueled wildfires and damaged crops in 2012 has now continued well into 2013.

However, long before the droughts and fires wreaked havoc, a team of scientists from the U.S. Department of Energy’s (DOE) Lawrence Berkeley National Laboratory (LBNL) and the U.S. Department of Agriculture’s (USDA) Grazing Lands Research Laboratories were already collaborating—to ask the question, “How do these events impact prairies, an ecosystem that once dominated the North American plains?”

In a recent paper, team leader Marc L. Fischer (LBNL), discusses how they may have found the beginnings of an answer in grass—or more accurately, the lack of it.

For two years, 2005 and 2006, rainfall on the U.S. Great Plains was lower than average. The DOE/USDA team used that time to capture the impacts of dry years and fires on prairies. In a controlled manner, they burned a pasture in Oklahoma that contained tall grass species native to the region. During the two years, the research team measured growth of grass species and the rate of exchange of carbon, water, and heat on the burned patch. The Atmospheric Radiation Measurement (ARM) Climate Research Facility, which maintains a large climate research facility in Oklahoma, provided the samples and instrumentation necessary for this team effort.

The scientists also made the same measurements on an adjacent unburned pasture that was similar in all respects to the one they burned. The results of the study appeared last December in the journal Agricultural and Forest Meteorology.

Fischer and his team found that under normal to somewhat dry conditions, like those of 2005, grass production during growing season—which follows the dry season when fires typically break out—captured most of the carbon that the patch had lost during burning. Grass production captures and stores atmospheric carbon, whereas decay and burning releases carbon back into the atmosphere; the latter produces soot and gases that release carbon faster than the slower decay process.

The capture and release of carbon is an important component of the carbon cycle—the continuous and life-sustaining process of recycling carbon between the earth, ocean, soil, organisms, and atmosphere. In 2006, however, which had a very dry growing season, Fischer and his team found that grass production was stunted both in the burned as well unburned fields: so much so, that both fields exchanged very little carbon. The researchers concluded that it is the dry conditions that the control the rate of carbon exchange rate on the prairies by reducing uptake.

Today prairie grasslands cover more than 20 percent of the Earth’s surface and hold more than 10 percent of the Earth’s total carbon inventory. To evaluate how drawn-out (at times for decades) extreme droughts and accompanying fires impact the carbon cycle on grasslands, the research team will start experiments to monitor carbon, water, and heat exchange rates in crop and prairie fields in the Southern Great Plains.