A bat guano-derived perspective on Holocene anthropogenic fire impacts in the southeastern USA

Humans have influenced fire regimes throughout history. However, in eastern North America the timing of the onset of human impacts on fire regimes remains debated. A principal problem in determining this timing is the difficulty of distinguishing human-caused fires from naturally-occurring fires in paleoenvironmental records. Here, we present charcoal data from a Holocene bat guano core in the southeastern USA, an archive and proxy combination which has recently been shown to reliably record human-caused prescribed burning. By comparing novel guano charcoal and pollen records, we find periods with elevated fire activity during the early to mid Holocene (12,000–5000 cal yr BP) and the last millennium. We interpret these data in light of previous research calibrating this proxy and archive, as well as archaeological data, to present the first reconstruction of human-caused fire in this region. While calibration studies of guano charcoal spanning beyond the modern era remain necessary, we find clear Holocene coupling of guano charcoal, regional paleofire activity, and archaeological site data, signifying a strong human influence on fire activity across local and regional scales in the southeastern USA. Further, we determine that changes in vegetation combined with increased human activity are the likely causes of Holocene increases in fire activity evident in our guano charcoal data. Our findings both agree and contrast with previous research suggesting a late timing of the onset of human impacts to fire regimes in eastern North America. This study further bolsters bat guano as a reliable paleofire archive and emphasizes the human influences on fire regimes, which are predicted to increase in frequency and severity in the future.