One of the coolest things about the ice age cycles of the last 2.5 million years is how species survived the various dramatic shifts in climate. One of the ways plants and animals survived unfavorable climatic phases was by retreating to relatively small areas 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).
The two main types of refugia are glacial and interglacial. The earth cycles between cold glacial and warm interglacial(literally meaning between glacial) periods. Some species are well-adapted to both periods, but many others strongly prefer one or the other. Species that prefer warm and/or more forested conditions will retreat to refugia during glacial periods(glacial refugia), and species that prefer cold and/or more open conditions will hide out in refugia during interglacials(interglacial refugia).
In general, interglacial refugia tend to be located at high elevations or high latitudes while glacial refugia tend to be at lower latitudes or lowland areas, especially along the coasts of warm bodies of water. However, a study by Hošek et al. that came out earlier this year goes into detail about a different kind 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 LGM(Stewart & Lister, 2001). This remained controversial despite genetic and fossil evidence, but the hot spring study lends further weight to it.
References
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
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
