In the far north of Finnish Lapland, where the boreal forest thins and open tundra begins, lie rare and fragile landforms shaped by ice: palsa mires. These wetlands are found only in areas of discontinuous permafrost, and they are among the most sensitive ecosystems in the world to climate change (Lindholm et al. 2005, Palmer et al. 2012, Fronzek et al. 2006).
On a field excursion in October 2023, I visited the Skalluvaara palsa mire, located about 6 km northwest of Stuorra Skállovárri, at around 280 meters above sea level. Here, the aapa mire where open fens, sedge-dominated lawns, and low ridges form a mosaic across the subarctic landscape ends and the Palsa zone starts. Palsas are the northernmost complex mire type — unusual, elevated peat mounds that owe their existence to ice (Sollid et al. 1998, Lindholm et al. 2005)
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| View into the palsa mire from the top of a pasla hill, palsa hill vegetation can be seen in the foreground |
What is a palsa?
A palsa is a peat-covered hill, often a few meters high, that contains a core of permafrost. The ice lens inside lifts the palsa above the surrounding wetland, creating microhabitats that are colder and drier (Hofgaard 2003, Sollid & Sörbel 1998, Kirpotin et al. 2003). Palsas can reach up to 7 meters in height and several meters across (Lindholm & Heikkilä, 2005). Their formation requires just the right balance of low temperatures, shallow snow cover, and moisture—a narrow ecological window that is increasingly threatened.
The Skalluvaara mire contains several active palsas, some still dome-shaped with intact frozen cores, others visibly collapsing (Lindholm & Heikkilä, 2005). Around them, the vegetation shifts dramatically. Sphagnum mosses dominate the wetter hollows, while the palsas themselves support more frost-tolerant species, including, Betula nana, and dry hummock mosses.
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| Sphagnum lawns around the Palsa hill, often Sphagnum riparium |
Zones of vegetation
One of the most striking features at Skalluvaara is the sharp transition in plant communities across the mire’s varied microtopography. The vegetation shifts from the ombrotrophic bog at the mire’s edge, across the dry, cold palsa hills, to the more nutrient-rich river siltation zone that cuts through the landscape.
This small-scale variation causes a high diversity of both bryophytes. Several mosses that require cold, stable conditions are restricted to the palsa hills. In contrast, water-dependent species such as Sphagnum cuspidatum thrive in the thawing pools surrounding the palsas. Nutrient-demanding species occur near the riverine transition zone—for example, Sphagnum teres—while species typical of nutrient-poor conditions, like Sphagnum fuscum, dominate the hummocks of the ombrotrophic bog.
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| Mylia anomala |
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| Neoorthocaulis floerkei |
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| Sphagnum capillifolium |
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| Sphagnum fuscum |
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| Sphagnum riparium |
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| Sphagnum russowii, Sporophyte |
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| Sphagnum teres at the river edge |
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| Splachnum sphaericum |
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| Sphagnum balticum |
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| Sphagnum cuspidatum |
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| Sphagnum lindbergii, Sporophyte |
A fragile system under threat
Palsa mires are acutely vulnerable to climate change. Their structure depends on permafrost close to the surface. As Arctic temperatures rise, the frozen cores begin to melt, causing the mounds to collapse. In their place, wet depressions and thaw ponds appear. This thawing of palsas has been observed across Fennoscandia and Western Siberia in recent decades (Bosiö et al., 2012; Shurduk et al., 2022). In Western Siberia, researchers have documented not only permafrost degradation but also increased biological activity in the peat and shifts in carbon cycling as previously frozen organic matter becomes available for microbial decomposition (Shurduk et al., 2022).
At Skalluvaara, you can see this change in action: some palsas are visibly sinking, forming wet margins colonized by Sphagnum cuspidatum and Sphagnum balticum.
This is not just a local concern. Palsa mires are carbon sinks, storing vast amounts of frozen peat. When they thaw, they release greenhouse gases—especially CO₂ and methane—into the atmosphere, feeding back into the warming cycle (Shurduk et al. 2022). Their loss also spells trouble for cold-adapted plants and bryophytes that depend on the unique conditions of frozen peat
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| Permafrost peatbog border. Storflaket, Abisko, Sweden. Photo by Dentren at English Wikipedia, licensed under CC BY-SA 3.0. |
Conservation and monitoring
Some palsa mires in Finland are protected within Natura 2000 sites, including Skalluvaara. But legal protection cannot halt permafrost thaw. What’s needed is long-term monitoring and climate action.
Researchers use a combination of remote sensing, ground-based temperature loggers, and vegetation surveys to track changes in palsa extent and degradation (Palmer et al., 2012). Spatial models suggest that even slight changes in mean annual temperature and snow cover can tip the balance—especially in low-altitude palsa fields like Skalluvaara, which are already near the southern climatic limit for palsa formation (Fronzek et al., 2006).
Without colder winters, there’s little hope of keeping the permafrost intact. Palsa degradation is likely to continue, potentially at an increased rate (Olvmo et al. 2020).
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| Transition zone between Palsa mire and river siltation zone with Eriophorum |
References
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Bosiö, J., Johansson, M., Callaghan, T. V., et al. (2012). Local variability of permafrost and vegetation conditions across palsa mires in sub-Arctic Sweden. Environmental Research Letters, 7(4), 045506. https://doi.org/10.1088/1748-9326/7/4/045506
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Fronzek, S., Johansson, M., Christensen, T. R., & Carter, T. R. (2006). Spatial modeling of palsa mires in relation to climate in Northern Europe. Climate Research, 32(1), 1–15. https://www.researchgate.net/publication/229944159
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Lindholm, T., & Heikkilä, R. (2005). Palsa mires in Finland. The Finnish Environment, 751.
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Palmer, S. C. F., Bragg, O. M., & Hanslin, H. M. (2012). Palsa degradation and hydrological change in northern mires. Mires and Peat, 10(2), 1–15. https://www.mires-and-peat.net/pages/volumes/map10/map102.html
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Shurduk, R. D., Pastukhov, A. V., & Turtseva, N. E. (2022). Permafrost thawing and changes of peat biological activity of palsa mire in Western Siberia. Environmental Research, 214, 114058. https://www.researchgate.net/publication/364265930
Sollid, J. L. & Sörbel, L. Palsa bogs as a climate indicator - examples from Dovrefjell, Southern Norway. Ambio 27, 287–291 (1998).
Kirpotin, S. et al. West Siberian palsa peatlands: distribution, typology, cyclic development, present day climate-driven shanges, seasonal hydrology and impact on CO2 cycle. International Journal of Environmental Studies 68, 603–623 (2003).
Hofgaard, A. Effects of climate change on the distribution and development of palsa peatlands. NINA Project Report 21, 32 (2003).Return to ref 2 in article
Olvmo, M., Holmer, B., Thorsson, S., Reese, H., & Lindberg, F. (2020). Sub-arctic palsa degradation and the role of climatic drivers in the largest coherent palsa mire complex in Sweden (Vissátvuopmi), 1955–2016. Scientific Reports, 10, 8937. https://doi.org/10.1038/s41598-020-65719-1Nature