Late Holocene anthropogenic and climatic influences on the regional vegetation of Mexico's Cuenca Oriental

• The settlement history of many regions of Mesoamerica remains poorly understood.
• We present a new multi-proxy paleoecological reconstruction from lake Aljojuca.
• The lake is in a semi-arid region in highland Mexico known as the Cuenca Oriental.
• The Aljojuca record documents Formative period settlement in the Cuenca Oriental.
• The record reveals dramatic landscape transformation following Spanish Conquest.

Scholars continue to debate the relative magnitude of pre- and post-Conquest anthropogenic landscape transformation in many regions of Mesoamerica. These debates have important implications for our understanding of the role of anthropogenic practices in the development, or at times degradation, of regional environments. Paleoecological records that provide long-term perspectives on climate change and human land-use patterns are critical to addressing these uncertainties. However, many regions of Mexico including the Cuenca Oriental, a semi-arid basin in the rain shadow of the Sierra Madre Oriental, remain poorly studied. We present a new paleoecological record from sediment cores recovered from Lake Aljojuca, located in the southern part of the basin. Stable isotope analyses of authigenic carbonates provide an independent record of past climate, while pollen and microscopic charcoal provide insights into past vegetation and fire history. The Aljojuca record is one of the only well-dated multi-proxy paleolimnological records from the Cuenca Oriental, and is one of few charcoal studies from highland Mexico. Zea mays pollen and increased fire activity at 2700 calendar years before present (cal yr. BP) suggest Formative period human settlement around the lake. Between 1700 and 800 cal yr BP, a drying climate combined with human uses of fire likely resulted in increases in the extent of xeric scrub vegetation. The Aljojuca record also documents important landscape changes during the historic period (~ 430 cal yr. BP–present) likely related to the introduction of invasive species and agricultural intensification. The Aljojuca record provides a unique perspective on human–environment relationships and highlights differences between landscape transformations in the pre- and post-Conquest periods.