Palsa mires of the Northern Hemisphere: environmental characteristics, degradation, and morpho-ecological state

Abstract

Palsas are unique permafrost landforms that are found in the peatlands of discontinuous and sporadic permafrost regions across the Northern Hemisphere. Palsa mounds create diverse microhabitats for both plant and animal species, making them important features that support the biodiversity of periglacial environments. In addition to their ecological importance, palsa mires also are linked to the global carbon cycle and greenhouse gas emissions through permafrost degradation. Future thawing of permafrost is projected to release large amounts of greenhouse gases from northern peatlands, which can further accelerate global climate warming. Therefore, the changing permafrost dynamics make palsa mires an interesting and critical research topic, one
that can help us to better recognize and understand the ongoing and future changes in periglacial environments.

The main objective of this thesis is to provide a comprehensive understanding of the environmental factors influencing the occurrence and morpho-ecological
state of palsa mires, and to predict future changes in palsa distribution. To achieve this, the thesis employs a multi-scale approach, integrating remote sensing data and statistical modelling across spatial scales ranging from circumpolar to local. First, the environmental characteristics of palsa mires in different parts of the Northern Hemisphere are examined by regional comparisons. Second, circumpolar changes in the suitable environments for palsas are predicted under three different future trajectories of greenhouse gas concentrations. Finally, the morpho-ecological state and degradation of palsa mires at the local scale are investigated in northern Finland.

The results show that palsa mires occur in narrow but regionally varying environmental settings, with climatic factors and soil moisture conditions playing a key role in defining suitable environments for the landforms. Without effective climate change mitigation, environments suitable for palsas are projected to almost completely disappear in the northern permafrost region by the end of the century. This projection is consistent with observations showing the overall poor morpho-ecological state of Finnish palsa mires and their significant degradation over the past 50 years. The results also highlight
the scale-dependent influence of environmental factors for the occurrence and state of palsa mires. While climatic factors were consistently important across spatial scales, the influence of seasonal freeze-thaw dynamics and soil moisture varied between larger-scale and smaller-scale studies.

This thesis highlights the urgent need to understand the impacts of climate change  on permafrost landscapes. The predicted dramatic loss of suitable environments for palsa mires underscores their vulnerability and the potential ecological consequences of their degradation. By integrating spatial modelling across different spatial scales, this thesis provides novel insights into the complex interplay between climatic and  environmental factors governing the distribution and state of palsas. The results improve our understanding of the ongoing changes in the northern permafrost regions and provide valuable information to support policymakers in planning conservation efforts and in making sustainable decisions regarding permafrost regions and peatlands.