Cambio ambiental y respuestas de la vegetacion de los últimos 17,000 años en el centro de México: El registro del lago de ZirahuZapotitlánn

Abstract

A 6.61-m-long sediment core (ZIR03-I) from the northern shore of ZirahuZapotitlánn lake (Michoacán, Mexico) represents the last 17 kyr with a hiatus between 12.1 and 7.16 kyr. Changes in plant communities and their relationship with the environment are documented with pollen analysis. Magnetic susceptibility, total organic and inorganic carbon analyses (TOC and TIC) and charcoal particles are used as proxies to infer paleohydrologic conditions in the basin and to document periods with abundant fire in the surroundings. The palynological record suggests slow change in local and regional vegetation during 17-12.1 kyr. Cool and dry conditions during 17-13.5 kyr are inferred from abundant Pinus forest and more subaquatic micro- and macrospores (Isoetes t-1). A change towards humid conditions at ca. 13.5 kyr is marked by increases in Alnus and Quercus and reduction in Isoetes t-1. Another period of higher moisture between 7.1 and 3.7 kyr is documented by an increase in mesophytic taxa. Canonical correspondence analysis demonstrated a relationship between charcoal particles and increases in magnetic susceptibility with terrestrial vegetation comprising herbaceous and disturbance elements. The increasing nutrients in the lacustrine system are recorded by the presence of Coelastrum and Staurastrum algae associated with eutrophic conditions. The trend of increasing humidity is reflected by higher TOC and increases in mesophytic vegetation. The presence of maize indicates the beginning of human activity at ca. 3.5 kyr around the basin. This is in agreement with the increasing abundance and diversity of herbaceous pollen.