Ecophysiological response of lowland tropical plants to Pleistocene climate

Climate changes associated with the Last Glacial Maximum (LGM, 21 kyr) are probably the most extreme that terrestrial vegetation, including tropical lowland ecosystems, have been forced to respond in over the past 100,000 years. The degree of tropical cooling can be reconstructed by paleoproxies that generally indicate a minimal cooling of 3_C and a maximum cooling of approximately 7_C (Guilderson et al., 1994; Stute et al., 1995; Mix et al., 1999; Behling and Negrelle, 2001; Mora and Pratt, 2001; Behling, 2002; Urrego et al., 2005; Punyasena et al., 2008; Blard et al., 2009; Williams et al., 2009). Some debate surrounds the degree of tropical decreases in glacial precipitation, primarily because precipitation patterns are strongly regional, and thus wide discrepancies in paleoprecipitation trends occur between different reconstructions. Despite this, a value of approximately 20% decrease in LGM rainfall is typically reconstructed from pollen-proxies in tropical catchments—such as the Amazonian Basin (Bush and Silman, 2004). Paleoclimate simulations of the South American monsoon during the LGM indicate an annual reduction in rainfall across Amazonia of between 25–35% relative to today (Cook and Vizy, 2006). Research also shows that glacial decreases in rainfall likely occurred in wet as opposed to dry seasonal months (Bush and Silman, 2004).