Ice cave palynology: A tool for reconstructing local vegetation history in the Austrian Alps

Ice caves are predominantly found in mid-latitude mountain regions, such as the European Alps. Those located near the alpine treeline are particularly valuable for reconstructing past vegetation dynamics in response to climate variability and land use. Despite the excellent preservation conditions provided by permanent ice cover, pollen preserved in ice caves remains an underutilized paleoenvironmental proxy. This study evaluates the potential of ice caves for local paleoecological reconstruction by analyzing pollen assemblages and plant macrofossils from two Austrian sag-type ice caves: Guffert-Eisschacht (1825 m a.s.l.) and Eisgruben-Eishöhle (1695 m a.s.l.). Organic-rich dark ice layers were sampled and dated by radiocarbon, covering a time span from the La Tène period to the Middle Ages. To distinguish local from regional vegetation signals, regional fossil pollen datasets and modern moss polster samples were also examined. Although pollen concentrations in the ice samples were lower than those typically found in lakes or peat bogs, preservation quality was excellent due to cryogenic conditions that inhibit microbial activity and oxidative decay. The pollen assemblages, supported by plant macrofossil evidence and modern analogues, reflect predominantly local vegetation, with minimal long-distance input. At Guffert-Eisschacht, Roman-period pollen and macrofossil evidence suggest a subalpine coniferous forest that transitioned to more open landscapes in the Middle Ages, likely due to intensified land use. In Eisgruben-Eishöhle, the Roman and Middle Ages samples also indicate greater landscape openness and diversity than today, shaped by a combination of favorable climate conditions and anthropogenic disturbances such as mining and forest clearance. Pollen-based vegetation estimates reveal clear shifts in plant composition across the two millennia, including upslope expansion of Alnus , Corylus , and Abies during the Roman Warm Period, and more open, human-influenced vegetation in the Middle Ages. These findings demonstrate that stratified ice cave deposits offer high-resolution, well-preserved, and locally reliable paleoecological archives. Their geographic location near sensitive ecotones, combined with multi-proxy data and robust chronologies, provides new insights into the complex interactions between climate variability and human activity in shaping alpine ecosystems. Ice cave records thus represent a valuable complement to more established paleoarchives such as lakes and peat bogs, enhancing our understanding of mountain ecosystem responses to environmental change. • Ice caves preserve well-stratified, cryogenically protected pollen and macrofossils for alpine vegetation reconstruction. • Pollen assemblages reflect mostly local high-elevation vegetation. • Vegetation shifts reveal interplay between climate variability and intensified land use over the last two millennia. • Ice caves complement lakes and peat bogs as valuable mountain paleoecological archives.