HOLOCENE CLIMATE CONTROLS ON FIRE AND VEGETATION IN NEOTROPICAL CERRADO SAVANNA ECOSYSTEMS

The Bolivian cerrãdo savanna lies within a climatically sensitive ecotone influencing fire activity and vegetation composition on centennial to millennial timescales. During the 21^st century, temperatures are predicted to increase by ~3ºC coupled with a precipitation decrease of ~20%. These conditions will reduce plant water availability and intensify drought stress, potentially altering vegetation composition and fire regimes. To provide a context to study the affects of future climate change on Neotropical savannas, a 24,000-year high-resolution sedimentary record was analyzed for charcoal and phytolith data from Huanchaca Mesetta, a cerrãdo savanna in northeastern Bolivia. Preliminary charcoal data from Huanchaca Mesetta suggest fire activity responds to fuel limitation resulting in decreasing fire activity during dry periods and increasing fire activity during wet periods. During the Last Glacial Maximum (LGM), fire activity was low, but increased during the late-glacial and Early Holocene as savanna vegetation established at the site. Phytolith analysis suggests that during the LGM, there was an abundance of arboreal phytoliths indicating the presence of forest cover, coupled with low fire frequency. Fires increased as a savanna developed during the Pleistocene-Holocene transition in response to the expansion of the South American Summer Monsoon (SASM). This suggests that during the LGM, a weakened monsoon characterized by reduced precipitation and convection, limited fire activity despite the forest cover that would have provided sufficient fuel for burning. High-resolution charcoal and vegetation records provide useful ecosystem analogs for conservationists, land-managers, and policy makers on cerrãdo savanna fires regimes during periods of increased warmth and drought stress as expected for the 21^st century.