Fire in the Swamp

By Jessie Griffin –

Coffee-colored water peels away from our boat, sending ripples across the glass surface of Lake Drummond. The ancient cypress trees begin to dance as our wake bends their reflections. We’re crossing this hidden, undeveloped lake at the center of a once-vast wetland stretching from southern Virginia across a million acres into North Carolina. Now the Great Dismal Swamp is reduced to (a still impressive) 110,000 acres, hemmed in by development. We have this otherworldly, placid coffee lake all to ourselves on an unseasonably warm December day.

As we approach the other side of the lake, the shoreline landscape changes abruptly from dense swamp to a vast swath of burnt toothpicks. In the past ten years, two massive wildfires have swept through the Great Dismal Swamp. The most recent fire in 2011, Lateral West, consumed 6,500 acres and burned for 111 days, despite 12.5 million dollars expended in suppression efforts¹. Not even the torrential rains of Hurricane Irene could squelch the fire.

Yet the swamp is inundated for half the year. Its organic soil, peat, is 85-95% water in its natural saturated state, and well known for its ability to retain moisture. How can a peatland burn?

Fire, it turns out, has been a natural process in the Great Dismal Swamp for hundreds, maybe even thousands, of years. Peat, composed mostly of decaying plants, contains a lot of carbon—read: fuel for fire—compared to other soils. It’s so rich in carbon that high moisture content does not necessarily prevent combustion. Dry it out, and the whole swamp basically becomes a tinderbox. The water table in the Great Dismal Swamp fluctuates seasonally, normally falling below the soil from July through November. Lightning can ignite surface fires that smolder for months in the soil. Many of the plant assemblages in the Great Dismal Swamp actually depend on fires to persist. Lake Drummond likely formed from a massive peat fire¹. But that’s not the whole story…

In May 1763, George Washington visited the Great Dismal Swamp for the first time and saw opportunity where its first colonial discoverer, William Byrd, famously saw a “horrible desert…toward the center of it no beast or bird approaches, nor so much as an insect or reptile exists.” Washington invested in the swamp and began a long history of ditching and draining it for agriculture and logging.

Today, 158 miles of logging roads and ditches traverse the swamp, severely altering its natural hydrologic cycle. Parts of the refuge that were once seasonally saturated have been drained, and when peat is left dry for too long, it transforms to a granular, oxidized state that will not re-saturate, even under flooded conditions. Centuries of logging have left a legacy of fuel for fire in the form of slash. Add hotter, drier weather patterns to the mix, a few strikes of lightning, and the resulting blaze will be visible from space.

As climate patterns increasingly shift, what role will peatlands play in the global carbon cycle? In many peatlands, inundation slows the rate of decomposition, and carbon-rich organic soils slowly build up. The organic soils in the Great Dismal Swamp, for example, are over 51 inches deep in places. Many scientists view peatlands as an important carbon sink because they store carbon below ground for long periods of time. When peatlands burn, they release the stored soil carbon into the atmosphere as greenhouse gases, and peat fires often smolder for months, reaching deep into the thick peat—the Great Dismal Swamp lost over a 39 inches of organic soil in some areas in the 2011 fire².

Peat fires are different from forest fires as we’re used to thinking about them. They are exceedingly difficult to extinguish, and the carbon emitted by burning soil can dwarf emissions from aboveground forest. The impact can be massive—Lateral West emitted much higher amounts of carbon per unit area compared to five other fires that burned mostly aboveground plants and trees². In 1997, massive peat fires in Indonesia released an equivalent amount of carbon to 13-40% of the average annual global carbon emissions from fossil fuels³. And most of that carbon came from the soil.

The U.S. Fish and Wildlife Service, in partnership with The Nature Conservancy, has been working for years to restore the hydrology of the Great Dismal Swamp, and balance the benefits and risks of wildfire—an already complex task that is likely to be exacerbated by climate change. Who knew that draining a swamp could have such dismal consequences?

References:

1. Great Dismal Swamp National Wildlife Refuge and Nansemond National Wildlife Refuge Final Comprehensive Conservation Plan. (2006).
2. Reddy, A. D. et al. Quantifying soil carbon loss and uncertainty from a peatland wildfire using multi-temporal LiDAR. Remote Sens. Environ. 170, 306–316 (2015).
3. Page, S. E. et al. The amount of carbon released from peat and forest fires in Indonesia during 1997. Nature 420, 61–66 (2002).

Additional information gathered from The Nature Conservancy, the Washington Post report on Lateral West, and the U.S. Fish and Wildlife Service.

Jessie Griffen is a second year graduate student in the Ecological Planning Program. She is grateful to Dr. William Old and Levi Old for an amazing voyage into the Great Dismal Swamp.