Out of the Woods:The Study of Archaeological Wood Charcoal

By Katie Alexander
University of Kentucky

In all places and times, humans have used fires for warmth, light, cooking, ritual, and more. And long after the flames have died and the embers have cooled, remnants of these fires remain.  These remnants include small black chunks of charcoal.  Under most conditions plant material will eventually decay in the soil, but once wood has been transformed to charcoal through exposure to fire, it can survive for millennia. Archaeologists can study this charcoal to learn about what kinds of wood people used for fuel, which in turn can provide evidence of what the environment was like at the time people were living there.

Archaeological charcoal fragments.

By examining charcoal under a microscope, even a piece as small as 2 mm in width can sometimes be identified.  This is because the patterning of the wood cells varies from one kind of tree to another. Some traits often used to identify wood such as color, density, and odor are obviously lost in burning. But wood retains many of its cellular traits even after its conversion to charcoal. These traits are observed on the archaeological specimens, and then compared to specimens of known wood types, published descriptions, and online photographic databases to try to identify them.

Examples of wood endgrains (top left-right: elm, hickory; bottom left-right: oak, maple). Image credits: www.wood-databse.com
 The cross-sections of archaeological charcoal magnified 40x under a microscope. Compare them to the wood examples above – which one do you think each most closely resembles?

Many things affect what kind of wood may be selected to build a fire. For instance, certain woods may be preferred for special purposes, some trees “self-prune” more than others meaning they produce more deadwood available for collection, and woods vary in how much smoke they produce or how hot they burn. Due to these factors, archaeological wood charcoal can never provide a complete representation of the entire environment. However, in day-to-day life, people will often choose fuelwood that is not only acceptable quality but also easily available, meaning it is likely to have been collected in the nearby area. By looking at the typical habitats and successional stages of wood types found in an archaeological charcoal assemblage, an archaeologist can learn about the surrounding environment of the site during the time people were living there.

For example, wood charcoal from some archaeological sites in the Midwest shed insight on how indigenous people shaped the landscape when maize was adopted as a crop.  Archaeological charcoal from this period includes multiple species that are known to be fast-growing and the first to grow in an area after it is cleared through some disturbance, which can include natural causes as well as human activities. The increased use of these species as fuelwood suggests a farming system in which land was cleared for cultivation, then left fallow for a long enough period for these species to grow before the fields were once again cleared.

Next time you are enjoying a campfire or bonfire, think about the evidence you are leaving behind for future archaeologists and what it might tell them!

References

Simon, Mary L. 2000. “Regional Variations in Plant Use Strategies in the Midwest during the Late Woodland.” In Late Woodland Societies: Tradition and Transformation Across the Midcontinent, edited by T. E. Emerson, D. L. McElrath, and A. C. Fortier, pp. 37–73. University of Nebraska Press, Lincoln, Nebraska.

Smart, Tristine and Ellen Hoffman. 1988. “Environmental Interpretation of Archaeological Charcoal.” In Current Paleoethnobotany: Analytical Methods and Cultural Interpretations of Archaeological Plant Remains, edited by C. Hastorf and V. Popper, pp. 167-205. The University of Chicago Press, Chicago, Illinois.

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