Fire and no rain

Posted by on Jan 27, 2017 in Uncategorized | No Comments

by Jess Riddle : Forest Ecologist

In northern Georgia this past fall, fires were never far from mind. Some days the reminder was the subtle hint of smoke in the air when you opened your door in the morning. Other days it was a thick pall of smoke that dulled the sun and chased people indoors.

That smoke came from dozens of fires across Georgia and adjacent states. There were two big ones on the Chattahoochee National Forest: the 27,870-acre Rough Ridge Fire and the 24,725-acre Rock Mountain Fire.  A lightning strike ignited Rough Ridge in the Cohutta Wilderness Area on October 16th. Over the next month and a half the fire spread across portions of Gilmer, Fannin, and Murray counties and out of the Wilderness Area. On November 9th, people started the Rock Mountain Fire along the Tallulah River.  This fire spread up through Rabun and Towns counties and into the Southern Nantahala Wilderness Area and North Carolina.

We are used to hearing about those kinds of scenes and acreages out West. This past year Georgia had Western weather – relative humidities in the single digits and months without substantial rain. Conditions became so dry that, in one instance, a vehicle parked on tall grass started a fire. The unprecedented drought allowed an unprecedented fire season. Now, people are asking what will happen to our forests and how can we protect ourselves in the future?

Lightning has been starting fires and igniting oak litter in the Southern Appalachians long before people set foot in the region.  That history gives me confidence that the forest can recover from these fires. I am concerned, however, that the extreme drought altered fire behavior significantly, possibly producing unusually severe effects that will take longer to heal.

Most natural fires produce a mosaic of different burn intensities. Fire will go out in wetter areas like north-facing slopes and streamsides, and even within areas that do burn, there will be a range of intensities, including unburned islands. Prescribed burns also strive for a fire mosaic, so within an 800-acre burn unit there might be 200 acres that don’t burn. This past year, though, even the streamsides and coves were dry, and rains never came to douse the interior before they reached each other.  The result was much more burns.

The same thing happened vertically. Fires typically consume leaf litter and the upper part of the duff layer, the dark, spongy blanket of decomposed leaves, twigs and other organic material that covers the forest floor. Normally, the upper part would keep the lower part moist, but this past fall the duff layer was dry all the way through. The Rough Ridge Fire consumed the litter layer and most of the duff layer on many ridges, and the entire duff layer in some covers. Many shallow tree roots growing in the duff and and upper soil layers burned.

These changes in the litter and duff layers may severely impact ground dwelling animals and streamwater quality. Many litter and duff dwellers like salamanders, millipedes, and firefly larvae likely survived by going deeper into the soil, but not all had that option. Those that survived emerged to find their habitat dramatically altered. Many plant species that normally avoid fire by growing in moist habitats also had no refuge. Of particular concern are trilliums and other cove species with shallow roots systems. Combined stress from drought and fire also will kill plants that would otherwise survive the fire. The effects on streams may be worse than those on the forest since exposed soils result in widespread erosion and increased flood risk. Spring will give us a much better picture of the effects, but trees certainly will be dying from both the fires and the drought for years to come.

You may have noticed I haven’t mentioned how hot the fires were, or catastrophic blazes.  The fires in the Cohutta Wilderness Area did not result in a desolate landscape of blackened snags. Similarly, the Forest Service response team determined 99% of the Rough Ridge Fire was “low severity”, and people reported mostly one- to two-foot flame lengths. Flames like those can kill small saplings and shrubs back to the ground and scar small trees. We observed most mature trees showed the fire only in a blackened lower trunk, and even small trees often survived. Forest Service assessors found only slightly more fire effects at the moderate- severity level, and an isolated area of high severity at the Rock Mountain Fire.

Fires in northern Georgia and adjacent regions severely impacted people too.  Although the smoke merely annoyed some people, it seriously threatened the quality of life of those with breathing conditions like asthma or chronic obstructive pulmonary disease. Others, like Joel Hitt (see his article on p. 5) had their lives temporarily upended by evacuations in the face of approaching fires.  And, of course, the tragic Gatlinburg, Tennessee fire killed 14 people.

Fires in Georgia might have caused similarly tragic loss of life and consumed dozens of homes without the heroic efforts of literally hundreds of firefighters.  The Rough Ridge and Rock Mountain fires likely would have been twice as large and spread into populated areas if not for control efforts. Firefighters also kept dozens of smaller blazes from turning into large conflagrations. These control efforts were successful despite rugged and remote terrain, historic drought conditions, and high winds.  Dry leaves falling onto fire lines further complicated matters by threatening to allow fire to escape containment. Firefighters battled these conditions for more than a month and over Thanksgiving. We owe them our thanks.

So how do we prevent putting so many people and properties at risk? For many, the answer is clear – more prescribed fire. That may be part of the solution, but I’m not sure the answer is so simple. The idea is that prescribed fires will limit the spread and intensity of future wildfires by not allowing a “dangerous fuel buildup” that could lead to more intense fires.

Weather, topography, and fuels control fire behavior. People can influence only fuels. Prescribed fires, though, do not simply combust everything flammable in their path. In our region, prescribed burns generally consume the leaf litter and some of the duff layer. However, they generally only kill, not consume, saplings and shrubs, leaving a constant or even increased amount of woody fuels (Fire Learning Network 2016; Waldrop et al. 2016). Since duff layer thickness exerts little control over fire behavior, prescribed fire affects future wildfire primarily through the litter and longer-term changes in the vegetation community.

Wildfires need a nearly continuous litter layer to spread.  The fall season following a prescribed fire largely replenishes the litter layer, and recovery is essentially complete after two falls. Hence, prescribed fires seem likely to primarily produce a short-term reduction in the risk of wildfire. Longer term effects involving vegetation changes likely will include both increased and decreased risk, depending on forest type. Extreme weather conditions, such as we had this year, generally will overwhelm other influences on fire behavior.  The Gatlinburg fire jumped from ridge to ridge driven by extreme winds in an extraordinary drought. Prescribed fire would not have prevented it.

The scientific literature shows that prescribed fires in arid and Mediterranean climates do indeed reduce wildfire spread and intensity (Fernandes and Botelho 2003). I have not been able to locate any similar studies in the Southern Appalachians. The closest I could find was a study in northern Mississippi that found prescribed fires did not reduce wildfire activity (Brewer and Rogers 2006). This past year in Georgia, the Rock Mountain Fire burned across the Chestnut Mountain burn unit that had been treated previously with prescribed fire four times, most recently 19 months ago. The Rough Ridge Fire had low intensities despite excellent conditions for fire spread: decades of fuel build up, historic drought, and days of extremely low humidity and high winds. These events call into question the relationship between site fire history and wildfire behavior in this region. More research is needed before we can be reasonably certain of the effects prescribed fire will have on wildfire.

The risk of wildfire damage depends on more than local forest conditions. Homes built in fire-prone locations like dry ridge tops or south-facing slopes are at elevated risk. Homeowners in those locations can reduce their risks by following steps recommended in Firewise community programs (www.firewise.org). The simplest way to reduce risk is by not starting fires.  Lightning started the Rough Ridge Fire, but the Rock Mountain and almost all other fires in Georgia this fall were human-caused. Finally, this drought was historic, but climate change projections consistently predict more extreme events for the southeast. By pulling together to limit carbon emissions, we can limit the number of times we have to go through another year like the past one.

For maps and more detailed information on the fall wildfires, see the Incident Information System (http://inciweb.nwcg.gov/state/11/#).

References:

Brewer, S. and C. Rogers. 2006. Relationships between prescribed burning and wildfire occurrence and intensity in pine-hardwood forests in north Mississippi, USA. International Journal of Wildland Fire 15:203-211.

Fernandes, P.M. and H.S. Botelho. 2003. A review of prescribed burning effectiveness in fire hazard reduction. International Journal of Wildland Fire 12(2):117-128.

Fire Learning Network. 2016. Fire Learning Network Southern Blue Ridge Workshop 11. May 17, 2016. Johnson City, TN.

Waldrop, T.A., D.L. Hagan and D.M. Simon. 2016. Repeated application of fuel reduction treatments in the Southern Appalachian Mountains, USA: Implications for achieving management goals. Fire Ecology 12(2):28-47.