The morpho-ecological state of palsa mires in sub-arctic Fennoscandia: insights from high-resolution spatial modelling

Palsas are unique permafrost landforms that contribute to periglacial bio- and geodiversity and store significant amounts of organic carbon. However, these landforms are highly sensitive to climate change and are degrading rapidly across the Northern Hemisphere. This study assesses the morpho-ecological state of all remaining palsa mires in Finnish Lapland under different climatic and topographical conditions, providing valuable insights into their future persistence. Using spatial multivariate modelling and high-resolution (10 m) geospatial data, we predicted the probability of a good morpho-ecological state of palsa mires. The predictions were evaluated against landform observations derived from historical orthoimagery. Our results show that 53 % of Finnish palsa mires have a low probability (<0.25) of being in a good state, while only 28 % have a high probability (>0.75). Plateau-shaped palsas were predicted to be in a better morpho-ecological state than smaller, dome-shaped palsas. Historical orthoimagery from the Paistunturi Wilderness Area¹ indicates a significant reduction in palsa area (−76 %) since the 1960s, and our model suggests a more moderate decline (−63 %) across Finnish Lapland. The results demonstrate a significant reduction in palsa areas over the past 50 years, emphasizing the critical influence of winter temperatures and precipitation on these changes. The research highlights the need for further monitoring of palsa degradation to better understand the impacts of climate change on periglacial landscapes and systems.