Climate-change-induced degradation of mires in Eastern Alps: A comprehensive resampling study of 200 mires after 35 years

Mires are among the most valuable and endangered ecosystems in the world. In the Alps, they are an integral component of the region’s natural, geographical, climatic, and cultural-historical diversity. Mires have been used by humans in many ways. Recent climatic changes and other human influences on mires are suspected of altering species composition. However, this assumption has never been comprehensively tested across a large number of mire sites in the Eastern Alps.

This study aimed to expand knowledge regarding the response and resilience of mire habitats and biodiversity after 35 years of environmental and anthropogenic influences and to determine the current state of native mire diversity in the Eastern Alps. In summer 2023, the vegetation of about 200 Austrian mires was resampled through more than 1000 vegetation surveys and compared with the plant diversity of the same mires recorded in the Austrian Mire Conservation Catalogue (Steiner, 1992) about 35 years ago (1984–1988).

Each vegetation survey was assigned EUNIS habitat types (Chytrý et al., 2020), regions, protection status, and altitude. We used indicator values of light, temperature, nutrients, reaction (pH), aeration, and moisture (Landolt et al., 2010) to examine the conservation status of these alpine mires and changes in climatic and edaphic site factors. Additionally, we analyzed long-term changes in plant diversity based on species richness, plant types, and red lists. The collected data supported selecting mires for restoration during the project period.

We compared the vegetation of mires from 1988 to 2023 and found that all six mire habitat types had degraded on average after 35 years due to less moisture, more nutrients, less light, and more aeration. The exceptions were Non-calcareous quaking mire, which showed no significant change in nutrients, and Tall-sedge bed, which showed only an average increase in aeration. An increase in the mean temperature indicator value, independent of altitude, was observed only for Poor fen in Northern and Central Alps.

On average, we observed a significant increase in plant species richness in all mire habitat types except Tall-sedge bed. The increase is attributable to species on the red list with the status “least concern”, as well as to woody plants and other herbaceous plants. This trend may not be positive for mires, as it suggests an increase in generalists rather than mire specialists.

We observed a reduction in typical mire plant types, such as a significant decline in mean peat moss (Spaghnum sp.) cover in Raised bog and a significant decline in mean sedge cover, except for Poor fen and Tall-sedge bed.

About one-third of all studied mire habitats showed negative trends regarding moisture, nutrients, and light. However, half were resilient in some way (only slight changes), and about 5 % even showed improvements (positive trends).