The environment of ancient cloud forests in the Mexican Pacific

Abstract

Two ancient cloud forests in the Mexican Pacific were reconstructed to reveal signals of past ecosystem responses to climate anomalies during the Late Holocene, Little Ice Age (~AD 1350-1850) and Medieval Climate Anomaly (~AD 800-1350). Applying palaeoecological techniques, two organic sediment cores were extracted from forest hollows: one from the cloud forest of the Acer Forest State Park (AFSP) and one from the Sierra de Manantlan Biosphere Reserve (SMBR), both in the state of Jalisco, Mexico. Fossil pollen was used as proxy for tree, herb and fern abundances, whilst carbonate and organic matter content, magnetic susceptibility and geochemical elemental composition were used as proxies for soil environment. Generalized additive models (GAMs) and tree regression models were used to discern the best soil-environmental variable that could explain tree, herb and fern abundances. Results showed a great diversity in taxa composition (110 taxa) with important spatial and temporal heterogeneity between the two forests. Carbonates and Mg were the most important variables explaining these plant assemblages. The driest period for the Little Ice Age was detected from ~AD 1650 to 1730 in AFSP and from AD 1528 to 1831 in SMBR; trees experienced a remarkable decreased, whilst herbs increased. For the warmest period of the MCA (AD 800-1200), herbs and ferns expanded, whilst trees contracted. The late MCA (AD 1200-1350) was acknowledged as a wet event with the highest expansion in trees.