Alternative grass and shrub states emerge in paleo-climatic cellular-automaton ecohydrology model simulations for central New Mexico

During last glacial cycle that peaked ~18,000 years (B.P.), the southwestern United States was much wetter and cooler than in the Holocene (last 11,000 years) and today. Since the Last Glacial Maximum (LGM), wetter and cooler climate in most arid and semiarid regions has generally transitioned to drier and warmer conditions, establishing their characteristic (i.e., today’s native) ecosystems and fire regimes 3,000 - 5,000 years B.P. We use the Landlab earth surface modeling toolkit to explore the implications of the climate since the late Pleistocene on ecosystem patterns, driven by a reconstructed climate. Alternative grass and shrubs states emerged as the modern climate established due to randomness in fire arrivals. The role of topography is explored. Our findings offer an explanation for observed shrub and grass ecotones under similar environmental conditions in central New Mexico.