As wildfires continue to become more frequent and larger in the Western United States, increasing amounts of carbon dioxide, a gas related to global climate change, are being released into the atmosphere. To better understand the carbon release, a Colorado State University forest ecology researcher is studying how large forest fires affect carbon storage on landscapes and the implications of more frequent forest fires for future climate change.
Dan Kashian, a researcher at Colorado State’s Department of Forest, Rangeland, and Watershed Stewardship, studied carbon storage across stand age and density classes in Yellowstone National Park to document the balance between carbon stored in live biomass and the forest floor and carbon released from decomposing dead wood. This balance affects whether a forest has a net release of carbon dioxide to the atmosphere, potentially contributing to global warming, or has a net uptake of carbon from the atmosphere.
"Yellowstone, like many places in the Rocky Mountains, is a place where fires are common and an important part of the ecosystem. It is typical here that wildfires will burn and subsequently kill all or most of the large trees in an entire forest. However, these forests are strongly adapted to fire, which is actually necessary to regenerate forests across large areas," Kashian said.
As forests burn, substantial amounts of carbon are released quickly from the forests into the atmosphere. Once the fires have ceased, large dead and decomposing trees across the landscape also release carbon over many years.
"A process that accompanies large forest fires is the large amount of carbon that is released into the atmosphere, both during the fire and for many years after. In our study, we found a predictable response of a lodgepole pine stand to forest fires in terms of carbon storage. Soon after the fire, the stand acts a source of carbon to the atmosphere as rotting dead wood releases carbon, but there is much less carbon lost to the atmosphere as forest age and trees become better at removing carbon from the atmosphere through photosynthesis," he said.
In his research, Kashian and his colleagues studied carbon storage in lodgepole pine stands aged 16-350 years to examine how it changes over long periods of time. They measured carbon stocks in live trees, dead wood, forest floor and soil. He found significant differences in carbon storage and distribution among these pools with stand age and density.
Lodgepole pine forests have experienced forest fires and subsequent changes in carbon storage for thousands of years. Kashian and his colleagues are concerned that climate change may cause large areas of forests to burn more frequently. When landscapes are burned by large fires like the 1988 Yellowstone fires, which burned almost 800,000 acres, it may take nearly 300 years for the forest system to recover to its original levels of carbon storage compared to the time before the fires burned. This long time frame means that large fires occurring more frequently may cause disruption in forest carbon storage at larger landscape scales.
"If climate change causes fires like those in 1988 to occur more often, the landscape will contain more young forests that lose carbon to the atmosphere, and fewer older forests will be present to store a lot of carbon. In turn, the additional carbon lost to the atmosphere could contribute to further climate change. So, if the big fires begin to burn large forest landscapes more frequently around the world, we could be in trouble from a climate change standpoint," Kashian said.
Kashian completed his research with Colorado State professors Michael Ryan and William Romme. He presented his research on stand-replacing fires and carbon storage at the Ecological Society of America annual meeting in Memphis, Tenn., earlier this month.
In fall of 2006, Kashian will begin a new position as an assistant professor of ecology at Wayne State University in Detroit, Mich.