More Fuel for Fire?

Photo courtesy of Federal Emergency Management Agency.

Fire has been a fact of life for millennia in the South, shaping the range and ecology of pine, certain oak, and palm forests. But along with shrinking polar ice and rising sea levels, there’s general agreement among climate scientists that climate change will probably increase both the intensity and frequency of fire in the southern landscape.

Current research from the Southern Research Station (SRS)confirms these predictions. A study published in 2010 by SRS Center for Forest Disturbance Science researchers Yongqiang Liu, John Stanturf, and Scott Goodrick examined global and regional wildfire potential using the Keetch-Byram Drought Index (KBDI), a tool developed by SRS scientists in the 1960s thats widely used to estimate landscape fire potential. A high KBDI value means an increased flammability of organic material on the forest floor that contributes to greater fire intensity. With higher values of KBDI, wildland fires are more intense and spread faster.

SRS researchers calculated future KBDI for the region using projections of temperature and precipitation provided by a regional climate model. They found fire potential increasing across the South in the near future (2041 to 2070), most significantly during summer and fall. They also found an increase in the length of the fire season, with the greatest increase in the Appalachian Mountain region, where the current fire season of 4 months (July to October) is projected to grow to 7 months (April to October) by the end of this century.

Fire frequency and intensity relate directly to fuel loading, the amount of fuel in forests available for combustion. Fuel loads tend to shift over time based on increases from forest growth on one hand, and removal through decomposition on the other. Both sides of the balance are impacted by moisture and temperature, which are expected to change under a changing climate regime.

SRS efforts to understand wildfire trends in a time of climate change can help define management options for mitigating impacts. One management option is prescribed burning, which reduces understory fuels, lessening the risk of wildfires. “Some case studies have shown that the number of wildfires in specific forests decreased over the past two decades with the increased use of prescribed burning,” says Liu. “A need for more extensive use of this tool is expected in the future in the face of the projected increases in wildfire potential.”

An oft-cited prediction for the South in a time of climate change is stronger and more frequent tropical storms. Goodrick says one area he’s pursuing relates to how these storms and wildfires interact. “After a major tropical storm, there’s a lot more fuel on the ground, including whole trees knocked down by wind. But the result isn’t always what you would expect. Big logs in moist climate don’t necessarily dry out enough to be part of the fire problem,” says Goodrick. In some conditions they can actually help to reduce fire, because they’re still too moist to burn the next year. More fuel doesn’t always mean more fire.”

Goodrick sees a take-home message for forest managers here. “The standard management response after a major windthrow event is extensive salvage logging,” he says. “But it may not be the best answer, because you may be removing something that can actually reduce fire.”

“Wildfire will likely play a larger role in southern ecosystems. The exact nature of that role will be determined by how the vegetation responds, and how fuel accumulation rates change,” says Goodrick.

Recommended reading:

Liu, Y.-Q.; Stanturf, J.; Goodrick, S. 2009. Trends in global wildfire potential in a changing climate. Forest Ecology and Management. 259: 685697. Access full text.

Liu, Y.-Q.; Stanturf, J.; Goodrick, S. 2010.Wildfire potential evaluation during a drought event with a regional climate model and NDVI. Ecological Informatics. 5: 418428. Access full text.

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