HOLOCENE RECORDS OF THE SIGNIFICANCE OF ENSO on VEGETATION AND FIRE REGIMES IN DESERTS AND SEMI-ARID GRASSLANDS OF THE UNITED STATES AND MEXICO

Desert wetlands (ciénegas) are dynamic systems that respond quickly to changes in climate conditions. Sediments from the San Bernardino Ciénega (near Douglas, AZ and Agua Prieta, MX) and the Cloverdale Ciénega (southwestern New Mexico) were examined to reconstruct the paleoenvironment and climate of this region, including changes in sedimentation, water availability, vegetation assemblages, and fire regimes to inform restoration efforts. Holocene vegetation and fire history records were reconstructed using fossil pollen and charcoal from both sites. Results from the fire reconstruction show a profound increase in fire activity with the onset of ENSO ca. 4500 cal yr BP at San Bernardino and a distinct increase in fire frequency associated with the Medieval Climate Anomaly. At approximately the same time standing water begins to occur on the Cloverdale site, suggesting that both sites are affected by increased ENSO variability. These fire data shed light on the long-term history of fire in desert environments and the relationship to precipitation regimes (ENSO) that may be helpful in understanding what fire regimes may be expected with global warming and how to best incorporate fire into management plans.