One of the most striking things about the glacial cycles of the last 2.5 million years is how species survived the various dramatic shifts in climate. Among the ways plants and animals survived unfavorable climatic phases was retreating to relatively small regions where conditions remained tolerable, and then using those areas as bases from which to expand their ranges during more favorable phases. These are aptly named refugia(singular=refugium).
Different species retreat to refugia at different times depending on their particular ecology, and the refugial locations of different species are also not the same. During glacial periods when large parts of the Earth become fairly cold, plant and animal species better adapted to warmer conditions retreat to “glacial refugia” where conditions are relatively warmer. Animals that really heavily on forests will choose areas where forests can still be supported.
In general, these glacial refugia tend to be located further south, at lower elevations, and nearer to the coast than the ranges of these animals during warmer interglacials. This is how temperate plants and animals of Europe survived brutal ice ages. However, a study came out earlier this year by Hošek et al.1 that goes into detail about a different category of glacial refugia that existed in Central Europe during the height of the ice age: hot springs.
The scientists located a geothermal site in the southern Czech Republic in the Vienna basin where temperate trees such as hazel, oak, and alder grew during the height of the ice, also known as the Last Glacial Maximum. They believe that the hydrothermal discharge created a relatively warm wetland that served as a refugium for temperate plants that would then rapidly colonize Europe north of the Alps as the glacial period was terminating.
The traditional view was that temperate plants only recolonized north and central Europe after the LGM from southern Europe, but some scientists have long suspected that there were small pockets in central and possibly even northern Europe where temperate adapted species were able to survive the harsh conditions of the LGM2. This remained controversial despite genetic and fossil evidence, but the hot spring study lends further weight to it.
References
1. Hošek, J., Pokorný, P., Storch, D., Kvaček, J., Havig, J., Novák, J., Hájková, P., Jamrichová, E., Brengman, L., Radoměřský, T., Křížek, M., Magna, T., Rapprich, V., Laufek, F., Hamilton, T., Pack, A., Di Rocco, T., & Horáček, I. (2024). Hot spring oases in the periglacial desert as the Last Glacial Maximum refugia for temperate trees in Central Europe. Science Advances, 10(22). https://doi.org/10.1126/sciadv.ado6611
2. Stewart, J. R., & Lister, A. M. (2001). Cryptic northern refugia and the origins of the modern biota. Trends in Ecology & Evolution, 16(11), 608–613. https://doi.org/10.1016/s0169-5347(01)02338-2