Does Prescribed Fire Damage Artifacts? Experiments in Midwest Parks

The research team collecting data during burn experiments. NPS.

National park managers have to balance restoring natural resources, which in many parks means wildland and prescribed fire, with preserving archeological and other cultural resources. The two goals can conflict, but studies show they need not, if managers have sound scientific information.

Most earlier research on fire and archeology came from the western and southwestern states, where big wildfires happen every year. Midwestern parks had no data on their own fire behavior or its effects on their resources. So the Midwest Archeological Center and the Midwest Region Fire Program designed experiments to measure how fire affects the kinds of archeological materials found at Midwestern sites.

The questions

• What fire conditions are typical of each Midwestern environmental zone?
• What conditions do head, backing and flanking fires create?
• What impacts, if any, do different firing techniques have on artifacts?
• Which environmental and fire conditions change surface archeological materials?
• Can minor impacts such as glazing, charring and sooting be cleaned off in the lab?
• Which kinds of artifacts are affected most and least?

Where

The NPS Midwest Region spans 13 states and several distinct ecosystems, with archeological sites from 12,000-year-old prehistoric camps to presidents' homes, so no single approach fits. The study chose two parks in each of three environmental zones:

In each park, sets of three plots were laid out at two locations chosen to reflect typical fuels, burn conditions and the archeological materials most at risk, and to fit burns the park had already planned.

How

Artificial sites. For each park the team assembled 192 objects, replicas, deaccessioned artifacts and artifacts with no known provenience, matching that park's archeology: replica stone tools and flaking debris, prehistoric pottery, bone and shell, and historic ceramics, bottle glass, kaolin pipes, metal cans, lead bullets and building materials. Each plot held 32. Every object was examined for existing wear and damage, measured, weighed and photographed before burning.

The burns. Weather, soil and fuel load were recorded before ignition. A data logger in the center of each plot read eight thermocouples every five seconds, with artifacts placed around the wire ends. Plots were lit as head, flanking or backing fires so that flame length, flame depth and rate of spread could be calculated.

Experimental artifacts in place after a prescribed burn at Effigy Mounds National Monument. NPS.

After the fire. Each artifact was checked for cracking, charring, sooting, combustive residue, fracture, scorching and melting, and its weight, size and color were measured again. Linking those changes to each fire's temperature and duration showed what the fire did.

What they found

• Most artifacts were not significantly affected.
• Combustive residue was the most common impact, on 48 to 75 percent of each assemblage in low to high amounts. With effort it came off durable materials such as glass and stone.
• Most impacts were temporary and could be removed by light to moderate cleaning, as cleaning and weathering tests showed.
• Serious damage, scorching, fracturing or melting, affected only 5 to 10 percent of the assemblages.
• Material and fuel mattered. Serious damage depended on the combination of fuel type and load with the artifact's material: bone, shell, leather, wood and lead were seriously affected more often than ceramic, stone, metal and glass.
• Fire was uneven, especially in woodland, because fuel types and loads varied from spot to spot.

Why it matters

The results give Midwestern park managers data and predictive models for their own ecosystems and materials, rather than relying on findings from other regions. They can better identify archeological resources threatened by fire, reduce or mitigate the impacts, and coordinate natural resource management with archeological preservation. The work is a first baseline that future studies can build on.

Sources

• National Park Service, "Exploring the Fire and Archeology Interface": https://www.nps.gov/articles/fire-and-archeology.htm
• The full project report is Experimental Study of Local Fire Conditions and Effects on Surface or Near-Surface Archeological Resources at National Park Service Units – Midwest Region, Joint Fire Science Program Project 06-2-1-05, funded through a cooperative agreement between the National Interagency Fire Center's Joint Fire Science Program and the National Park Service. Methods built on Buenger (2003).
• The NPS article names the Kansas park "Tall Grass Prairie National Reserve"; this page uses its name, Tallgrass Prairie National Preserve.