Classifying Microscopic Charcoal Morphology to Improve Understanding of Fire History in Sediment Records from Neotropical Lakes

Keywords: charcoal morphology, fire history, lake sediments, prehistoric agriculture
Session Type: Virtual Paper Abstract
Day: Tuesday
Session Start / End Time: 3/1/2022 03:40 PM (Eastern Time (US & Canada)) - 3/1/2022 05:00 PM (Eastern Time (US & Canada))
Room: Virtual 17

Abstract

Charcoal fragments in lake sediment cores are proxies for past fire activity. Charcoal presence indicates fire occurrence, while charcoal morphology—particle shape, size, and features—can reveal the types of vegetation that burned. Many studies of pollen have included quantification of microscopic charcoal on pollen slides to explore temporal relationships between vegetation and fire. Classification of microscopic charcoal morphology can provide information on fuel types and hint at whether fires were intentionally set by people. We have developed a classification system for charred microscopic particles using a reference collection developed from laboratory charcoalification of modern plant samples and the limited literature on charcoal morphology. The classification system includes three primary morphological types: graminoid leafy, dicot leafy, and woody. Graminoid leafy and woody types are further subdivided into multiple morphological categories. Here we present results of morphological classification of microscopic charcoal on pollen slides spanning the last two millennia from two sites in southern Pacific Costa Rica with histories of prehistoric agriculture, forest recovery, and historic agriculture. These sites are Laguna Zoncho, from which we examined multiple cores, and nearby Laguna Santa Elena, from which we examined one core. Previous proxy analyses reveal differences in fire history and the timing of prehistoric agricultural decline or abandonment at these sites. Our goal is to compare charcoal morphologies in multiple cores from Laguna Zoncho, and between Lagunas Zoncho and Santa Elena, to test whether the new classification system can improve understanding of prehistoric fire activity as influenced by humans and climate.