February 15, 2003
Preliminary findings from computer modeling studies of the 2002 Colorado forest fires indicate wildland fires are taking tons of carbon out of “storage” in evergreen forests and feeding it into the atmosphere as carbon dioxide, a primary greenhouse gas.
The prolonged Colorado drought made conditions worse, stunting tree growth and turning forests into tinderboxes. Further diminishing forests’ ability to store carbon is human activity and land use changes, researchers found.
The conclusions were the result of research conducted by a team of researchers from Colorado State University, the U.S. Geological Survey and the National Center for Atmospheric Research, and were presented at the annual meeting of the American Geophysical Union in San Francisco in December 2002.
“We’re using the western U.S. as a case study area where climate and land use are interacting in several interesting ways,” said NCAR senior scientist David Schimel, who collaborated with Dennis Ojima of CSU and Jason Neff of the USGS.
Western lands — especially evergreen forests — represent roughly half of carbon storage in the U.S., according to NCAR. Changes in land use, fire suppression strategies and climate all have the potential to increase wildland fires.
The researchers developed a new computer model of a complex forest ecosystem to simulate the release of carbon during the 2002 fire season in Colorado. The findings estimated how much carbon would be stored in a normal year compared to a drought year, such as 2002. More carbon is freed from storage during droughts, not only because more tinder-dry vegetation burns, but because plants deprived of water grow more slowly, absorbing and storing less carbon in their tissues. Forest fires, it was determined, had a significant effect on the regional carbon balance, changing Colorado from a storage area to a source of atmospheric carbon. Since carbon circulates globally, the Colorado fires had a very small effect on the global carbon budget, the researchers found.
The research team is also using computer models to compare different approaches to reducing wildland fire risk. To simulate regrowth of burned areas over the next 30 years, the team used a scenario that includes the effects on vegetation growth rates of elevated carbon dioxide. The researchers then compared different fire management strategies.
“We don’t know which method takes more carbon out of storage, mechanical thinning or prescribed burning, but that’s one of the questions we’re looking at,” Schimel said.
Computer models have been used before to estimate how much carbon dioxide is circulating in the atmosphere, how much is stored as carbon in vegetation and soils, and how much is shifting between land storage and the atmosphere.
However, “it’s much harder to take the system apart than early modeling efforts suggested,” said Schimel. For example, increasing road density in the West has been correlated with increasing wildfires. Both the presence of more people to ignite fires and the impact of roads on surface and groundwater are implicated. Forest clear-cutting and road-building channel away water formerly held in place by the living forest floor, causing a drop in the water table.
The current project incorporates land use, drought, soil health and other factors to better capture the complexity of ecosystem interactions at the local level.
Projections of climate change in the West include hotter temperatures and increased drought, key factors for more forest fires.
Based on early findings of the NCAR/CSU/USGS project, “we’re either going to be spending a lot more money on fire suppression or we’re going to be seeing a lot more carbon released by wildfires,” Schimel said.