Interpreting Paleo Proxies from California's Sierra Nevada: Charcoal as Climate, Pollen as People

Keywords: paleoecology, Sierra Nevada, California, pollen, charcoal, fire
Session Type: Virtual Paper Abstract
Day: Monday
Session Start / End Time: 2/28/2022 02:00 PM (Eastern Time (US & Canada)) - 2/28/2022 03:20 PM (Eastern Time (US & Canada))
Room: Virtual 8

Abstract

In the western United States, paleoecological proxies such as pollen and sedimentary charcoal are often used to reconstruct past environments, with some researchers assuming trends in these proxies solely reflect climate. Humans worldwide have used fire to alter landscapes for hundreds of thousands of years (Roebroeks and Vill 2011; Walker et al. 2016), and hunter-gatherer populations are more likely to use fire as a tool when vegetation is fire-adapted (Coughlan, Magi, and Derr 2018). Given that indigenous populations have lived in fire-prone present-day California since at least the terminal Pleistocene, it is reasonable to expect these proxy records may contains signals of human influence. In this paper I present results comparing the relationship between sub-centennial pollen and sedimentary charcoal reconstructions from five sites (three pre-existing, two new paleoecological sites) along the central and southern Sierra Nevada range of California against independent, tree-ring-derived climate reconstructions to examine whether reconstructions derived from these proxies are indeed climatically driven, or whether the reconstructions may elucidate human influence. I use pollen reconstructions to derive a vegetation response index (VRI) to compare shifts in taxa against climatic expectations. At these sites, charcoal reconstructions typically align with climate, but VRI shows periods where forest response is counter to climatic expectations. The above deviations align with the timing of archaeological site use (where available). These results suggest that sedimentary charcoal generally agrees with climate, but pollen may be an indicator of people influencing their environment, even in non-agricultural and non-pastoral environments.