Multi-proxy paleoecological analysis of a high-altitude site in central Mexico: Holocene vegetation dynamics,pond development and climate variability

High-mountain lakes constitute key archives of past environmental dynamics and climate change. This study aims to reconstruct Holocene vegetation dynamics, fire regimes and hydroclimatic history of a high-altitude pond in central Mexico using a multiproxy approach. The Nahualac pond is located on the NW flank of the Iztaccíhuatl volcano at 3900 m asl. This multiproxy investigation integrates the analysis of pollen, non-pollen palynomorphs, diatoms, cladocerans, ostracods, chironomids, testate amebae, charcoal, and sediment geochemistry. Three stages of environmental change were identified. The first stage (8.4–6.6 ka) was characterized by a wetland environment with alpine grasslands, and low fire activity. In the second stage (6.6–4.7 ka) planktonic diatoms increased, and there was an upward displacement of the montane forests dominated by Pinus, Quercus, and Alnus and enhanced fire activity. A transitional period (4.7–4.2 ka) showed dry-cold environments, similar to those of the first stage. The third stage (last 4.2 ka) was characterized by wetter conditions and fluctuating water levels. A first interval (4.2–3.5 ka) recorded a shallow pond with planktonic diatoms, cladocerans, and ostracods indicating cold winters, the establishment of Pinus forest, and increased fire activity. From 3.5 ka to the present, a pond ecosystem with complex trophic interactions developed. Three drought events were identified at ~3.2–2.7, ~2.0–1.9, and ~1.2–1.1 ka. Overall, Nahualac provides a robust high-altitude reference showing how interactions among temperature, seasonality, and moisture balance governed ecosystem dynamics and fire regimes in the central Mexican highlands over the last 8.4 ka.