CLIMATE, FIRE, AND HUMAN HISTORY IN CENTRAL AMERICAN SAVANNAS: NEW PALEOENVIRONMENTAL RECORDS FROM BELIZE AND COSTA RICA

The factors that determine boundaries between savanna and forest vegetation in Central America have generated debate. In some areas, savannas are not regarded as the “natural” vegetation but instead as a type of disturbance vegetation created by the activities of European settlers or Indigenous occupants. Lake sediments are natural archives of past environmental conditions, and studying proxies in sediment cores from savannas can shed light on their history, including the influences of fire, climate, and people. Trends in vegetation and fire, inferred from pollen, bulk stable carbon isotopes, and charcoal, can be used to infer changes in climate, but vegetation and fire can be strongly affected by human activity. Records of paleohydrology from compound-specific hydrogen isotopes are used to reconstruct hydroclimate independent of human activity. In this thesis research, I analyzed charcoal and bulk stable isotopes in lake-sediment cores from the grass savannas in the El General Valley of southern Pacific Costa Rica, and developed a compound-specific hydrogen isotope record of hydroclimate and a carbon isotope record of vegetation from a Belizean pine savanna. The Belizean hydrogen isotope record documents shifts in paleohydrology indicating relatively wetter and drier periods over the last ca. 5000 years. Dry intervals at 2495, 1781, 379, and 53 cal yr BP are consistent with dry events recorded in other records from the region. Charcoal data show a continuous history of fire. However, some isotopically-inferred wetter intervals correspond to charcoal-inferred periods of enhanced fire, suggesting that humans, rather than climate, were the primary driver of fire on the landscape. From the Costa Rican lakes of Redonda and Larga, I established preliminary records of paleoenvironmental change that extend to the late Pleistocene. The two lakes show distinct characteristics including differences in amount and sources of organic matter, and in stable carbon isotopic composition. Low microscopic charcoal concentration and influx at Laguna Redonda indicate that charcoal preservation is poor at the site, or that fires were not as frequent as expected for lakes in savannas.