Vegetation Composition
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Improve vegetation composition in mires under restoration
Improving
Koitajoki Watershed
Finland
Problem: Approximately 72% of peatlands in the Koitajoki watershed are degraded, primarily because ditches have been dug to drain them in order to make the land suitable for growing timber. Peatlands are typically carbon sinks because the vegetation present facilitates carbon sequestration, but when they dry out they lose those species and become large sources of greenhouse gas emissions.
Action: Snowchange is refilling the ditches, which allows new water flowing into the area to remain on site, eventually saturating it with water and promoting the presence of the plant species that are typical of a healthy, wet peatland.
Indicator: A recovering peatland will gradually show a shift in species composition, similar to the composition found in natural, undegraded sites that have never been drained. This in turn will improve habitat for other species including wading birds.
Methods
Snowchange is monitoring the vegetation across two mire areas, Rahesuo and Valkeasuo. Because the topography in a single mire can produce substantially different vegetation compositions, sampling plots were stratified by topography and mire type. In Rahesuo, sites are spread across three condition categories: pristine or near natural, restored, and ditched. The natural condition includes plots in raised bog ridge, lawn and Fuscum bog hummocks, each with 15 sampling plots (Fig. 1). The restored condition includes plots in degraded raised bog ridge, lawn and cotton grass pine bog. The ditched condition includes plots in degraded cotton grass pine bog and raised bog.
In Valkeasuo, there are five different condition categories, each with between 15 and 20 sampling plots. Three of these condition categories are degraded: degraded meso-eutrophic pine fen, oligotrophic tall-sedge pine fen, and Fuscum pine bog. The other two condition categories are natural or moderately disturbed: oligotrophic tall-sedge pine fen and raised bog.In both Rahesuo and Valkeasuo, comparing vegetation in plots from non-degraded sites to vegetation at degraded sites that are undergoing restoration through ditch refilling will enable better understanding of the baseline status of degraded sites as well as the process of recovery as vegetation composition changes. The middle part of the Rahesuo ditches was refilled first in 2022, and in the ditched site, they will be refilled in 2025. In Valkeasuo, restoration started in November 2024.
Figure 1: Map of monitoring sites in Rahesuo (left) and Valkeasuo (right).
In Rahesuo, sampling plots are 50 x 50 cm. In each plot, percentage cover is recorded for all species in the plot, following Pitkänen et al., 2013. Percentage cover of different species is then analysed statistically to identify indicator species for the natural and degraded sites. These indicator species can then be used to assess recovery of the degraded sites. As restoration progresses, an increase in coverage of natural condition indicator species and a decrease in coverage of degraded condition indicators would be expected.
Results
At Rahesuo, water table monitoring shows that the level of the water table rose at all sites from 2023 to 2024 (Fig. 2).
Figure 2: Water table levels of Rahesuo sites in 2023 and 2024. Sites 8 and 9 were added in 2024 and are not included here.
Using indicator species analysis, the indicator species selected for natural and degraded conditions across both Rahesuo and Valkeasuo were:
Natural condition: % cover of Sphagnum species
Degraded condition: % cover of Pleurozium schreberi, Polytrichum species, Dicranum species, Cladonia species, and bare peat.
Between 2023 and 2024, the average % cover of natural condition indicators at degraded sites showed a statistically significant increase, suggesting early signs of vegetation recovery (Fig. 3). While the average % cover of degraded condition indicators also decreased at degraded sites, this was not statistically significant. There was no statistically significant change of either indicator in natural sites.
Figure 3: Change in % cover of indicators species for natural condition (top) and degraded condition (bottom) at Rahesuo. There was a statistically significant increase in coverage of natural indicators at degraded sites, indicating early signs of recovery.
In Valkeasuo, baseline data collected in 2024 showed that degraded sites had a median of 40% cover of degraded condition indicators (range 0-100%) and 50% cover of natural condition indicators (range 0-100%). In contrast, natural sites had a median of 0% cover of degraded condition indicators (range 0-90%) and 100% cover of natural condition indicators (range 10-100%). Changes in these indicators following restoration will be monitored over the coming years.
Vegetation composition of plot 10A at Rahesuo in 2023. Photo: Tiina Oinonen.
The same plot in 2024, showing recovery of the orange-coloured moss Sphagnum balticum, an indicator of natural condition. Photo: Tiina Oinonen.
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