Compass Magazine - Issue 18

Perspectives and tools to benefit southern forest resources from the Southern Research Station

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More Fuel for Fire?

by Susan Andrew

Rising temperatures may restrict native eastern brook trout to higher elevation coldwater refuges.

Climate change will probably increase both the intensity and frequency of fire in the southern landscape. (photo courtesy of the U.S. Fish and Wildlife Service)

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 is general agreement among climate scientists that climate change will probably increase both the intensity and frequency of fire in the southern landscape.

In its 2007 assessment, the UN Intergovernmental Panel on Climate Change cited multiple studies that link the spread of wildfires to the warmer, drier conditions already found in many regions due to rising temperatures from climate change. General circulation models used for weather and climate forecasting predict that by the end of this century, there will be an overall warming and drying trend in a large portion of the subtropics and middle latitudes of the world, including the Southeastern United States—conditions that are expected to also bring an increase in wildfires.

Current SRS research confirms these predictions. A study published last year by SRS Center for Forest Disturbance Research researchers Yongqiang Liu, John Stanturf, and Scott Goodrick examines global and regional wildfire potential using the Keetch-Byram Drought Index (KBDI). This tool was developed in the 1960s by two SRS scientists and has become a widely used estimate of 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 that fire potential increases 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.

"We're projecting an extended fire season, including in the Coastal Plain, where those afternoon thunderstorms that can help put out fires may have a delayed onset," says Goodrick. In addition, when they project forward towards the end of the century using a model that reproduces current conditions, "we see a slight increase in dryness in May and June—that's when a lot of our acres burn. A small change at that time of year means that we'll be fighting more significant fires then. At the very time when we have our peak fire conditions, our conditions are going to be worse."

Climate change will probably increase both the intensity and frequency of fire in the southern landscape. (photo courtesy of the U.S. Fish and Wildlife Service)

In another recent study by Liu and colleagues from Auburn University, the authors predict changes in fuel loads in response to projected changes in climate in the South for the period 2002 to 2050. The researchers found that by 2050, reduced precipitation will lead to a small decline in fuel load for the region as a whole because of reduced forest growth. This will be the case, the researchers argue, despite projections of increased forest growth driven by CO2 availability and increased nitrogen deposition. However, this study revealed a lot of variability across the South when it comes to fuel loads, owing to different climate effects anticipated in various places. For instance, a decline in precipitation in the northern inland section of the region may lead to a 20-percent reduction in fuel load for the forests of Tennessee and Kentucky, while elevated precipitation and decreased daily mean temperatures in coastal areas of Virginia and the Carolinas may result in increased fuel loads there.

Burning to Reduce the Risk

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, lowering the risk of wildfires. "Some case studies have shown that the number of wildfires in specific forests has decreased gradually in 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 increase 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. "In a moist climate, big logs 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 wind 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 is likely to 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. "In the future, fire conditions are likely to be bad, but due to the possibility of lower fuel loads, they won't be as bad as they could have been. Yet even under the best foreseeable future, wildfire is still likely to be worse than it is today."

For more information:

Yongqiang Liu at 706–559–4240 or yliu@fs.fed.us

Scott Goodrick at 706–559–4237 or sgoodrick@fs.fed.us.