Ecosystem-Vegetation Dynamics in Sub-arctic Stordalen Mire, Sweden
Mugnani, Maria Paula
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Increased global temperatures have contributed to the thaw of permafrost and a subsequent atmospheric production and release of methane (CH4) from subarctic ecosystems. Other climate change-related developments, including seasonal abnormalities, might alter vegetation diversity and abundance. I measured vegetation composition and percent cover-based abundance in five distinct ecosystems two hundred kilometers north of the Arctic Circle in Stordalen Mire (68° 21’ N, 19° 03’ E), a subarctic peatland near Abisko, Sweden. These five ecosystems included palsa, Eriophorum-dominated fen, Sphagnum-dominated peatland, lakeshore edge and lakeside heath. The mire is an area of discontinuous permafrost populated by micro-ecosystems that vary in plant species and soil nutrients that provide beneficial services to support a range of life forms including rodents, birds, insects and reindeer. In the vegetation data analysis, lakeside heath had the highest mean species quantity, evenness and diversity based on the Shannon Diversity Index. It had a mean of nine species and a 1.80 diversity value, followed by lakeshore edge, palsa, Sphagnum peatland and Eriophorum fen. High lakeside heath diversity can be associated with its high ammonium concentrations and medium water table depth, which created a variety of niches for high growth form diversity. In both species diversity and mean species quantity, the other sites were significantly different from each other except between palsa and lakeshore edge and Eriophorum Fen and Sphagnum peatland (p<0.05). In soils results, the mean total carbon decreased along the moisture gradient, with Eriophorum fen the lowest and dry palsa the highest. The high carbon in the palsas can be attributed to the presence of permafrost, which maintains accumulated organic matter frozen with minimal decomposition. Sites did not differ in C:N ratio except for Sphagnum peatland, which had the highest ratio at 68:1. This large quantity of carbon could due to waterlogged conditions or slow rates of nitrogen mineralization due to slow decomposition. Vegetation composition varied between ecosystems, especially in the palsas that supported mostly low-lying dry-tolerant species, not found in the wetter, anaerobic ecosystems. The wet, less diverse ecosystems contained several highly dominant species observed to be moving into drier sites. The results, combined with recent studies indicating permafrost thaw, suggest changing mire dynamics to wetter and more homogenous in vegetation, likely reducing total carbon and the lakeside heath niches and anaerobic-intolerant species. Thawing permafrost would promote higher CH4 emissions owing to wetter conditions and dominance of sedges that facilitate CH4 emission through vascular plant transport. In the future, vegetation shifts and soil characteristics within subarctic peatlands like Stordalen Mire can be used as indicators of changing ecosystem dynamics in thawing permafrost and methane emissions with possible climate impacts.