1580 years of human impact and climate change on the dynamics of a Pinus-Quercus-Abies forest in west-central Mexico

The present research involved vegetation and environmental reconstruction of a Pinus-Quercus-Abies dominated forest in west-central Mexico over the last 1,580 years. Paleoecological techniques such as the analysis of pollen, micro-fossil charcoal particles, and geochemical elements were used to document changes in the taxonomic composition of vegetation and its relationship with anthropogenic activities and climate change. Chronology was determined using C-14 dating and the age-depth model was constructed by linear interpolation. A redundancy analysis (RDA) was performed to identify patterns in composition of taxa and environmental variables and a cross-correlation analysis between taxa and micro fossil charcoal particles to determine synchrony. Results of the palynological record indicate that Pinus has been the dominant taxon throughout the sequence, together with codominant taxa such as Quercus, Abies and Alnus. Cross-correlation analysis indicated a positive correlation with Pinus and Ternstroemia, both in synchrony with micro-fossil charcoal. RDA showed that Pinus, Asteraceae, Poaceae, Phaseolus and Zea are associated with forest fires. Two events of climate change were identified: the Medieval Climatic Anomaly (MCA) (similar to 950-1400 AD) and the Little Ice Age (LIA) (similar to 1350-1850 AD). Main vegetation responses were the expansion of pine forest in the beginning of the ACM and a decrease at the end of this period; throughout the PEH, vegetation fluctuated in the composition of taxa. Pollen of cultural taxa such as Amaranthaceae, Asteraceae, Phaseolus, and Zea suggests the existence of human impact from similar to 1,580 AD to the present. The evidence points to complex patterns in response of the vegetation during periods of environmental change, which may offer new scenarios for assessing the impacts of local climate change.