Morphometric characteristics of charcoal produced from plants native to the southeastern United States of America (USA)

Charcoal shape variations provide insight into past fuel types burned, with charcoal length:width (L:W) being the most popular means of distinguishing fuel types. This paper presents morphometric data (L:W) of charcoal produced from plant taxa (n = 21) native to the southeastern United States of America (USA). These taxa included monocots (n = 3), dicots (n = 12), and gymnosperms (n = 6), which represented a range of growth habits including graminoids, trees, shrubs, and subshrubs. We further divided these taxa into tissues (n = 36 total samples) which included leaves, wood, bark, needles, stems, and a seed pod. Our results show that charcoal produced from plants native to southeastern USA exhibits more variable L:W values than those tested in previous research, but that when aggregated, they broadly agree with published L:W value ranges. Within the dicot group, leaves produced charcoal lower L:W values (median = 1.92, interquartile range (IQR) = 1.33) than wood (median = 2.43, IQR = 3.00), whereas the opposite was true for gymnosperms whose needles produced greater L:W values (median = 2.60, IQR = 3.22) than wood (median = 1.93, IQR = 1.44). The monocot graminoid we tested produced greater L:W values (median = 3.47, IQR = 6.02) than dicot or gymnosperm fuels. Further, our results provide conflicting perspectives on the likelihood of evolutionary relationships as the cause of variations in charcoal L:W values. Last, our results underscore the importance of site-specific experimental charcoal approaches to enable robust paleofire applications of charcoal morphometry.