What bog-builder can hold 15-20 times its dry weight in water?
Sphagnum moss!
by David McNicholas
As an ecologist working on Ireland’s peatland restoration, I’ve seen firsthand the profound transformation of re-wetting former industrial peatlands, and its capacity to enhance biodiversity and carbon storage. Working as a member of the Bord na Móna Ecology Team with funding provided by the EU’s Recovery and Resilience Facility as part of Ireland’s National Recovery and Resilience Plan, I’ve have seen more than 60 peatland sites undergo this incredible transformation. Following extensive ecological, hydrological and engineering studies to create the optimal conditions for Sphagnum moss establishment, it is exciting to now move towards the active planting of Sphagnum moss back onto these peatlands. This will accelerate the establishment of Sphagnum-rich bog vegetation that will have greater biodiversity and climate benefits at scale.
Raised bog formation
Sphagnum moss species are key plants in the development and existence of bog habitats. Some species can hold 15 to 20 times their dry weight in absorbed water and tolerate very harsh conditions such as nutrient deficiency, high acidity and waterlogged environments. This ability of Sphagnum to hold water creates the quaky surface conditions that are characteristic of raised bogs in good condition. Bogs simply would not exist as we know them without Sphagnum.
Raised bogs begin to develop in wet shallow depressions, often shallow lakes. Over time, wetland vegetation such as reeds, rushes and other plants leave dead matter behind in the substrate. As the amount of dead vegetation accumulates, the layer of growing vegetation on top is eventually lifted above the influence of the local groundwater. At this point, this layer has become ombrotrophic (exclusively rain fed). The result, in wetter climates, is the development of a wet, nutrient poor and acidic environment in which Sphagnum species thrive. Sphagnum is known as an “ecosystem engineer”. This moss can change its environment, making it wetter and more acidic, suiting these mosses and creating perfect peat-forming raised bog. As the living plants grow upward, the Sphagnum tissue beneath the living surface of the bog is submerged beneath the weight of the growing layer above. This dead material does not completely decay in the anoxic, waterlogged conditions. Instead, it will become peat over time, while the living material will continue to grow, driving the formation of a raised bog dome.
Sphagnum’s role in carbon sequestration
The growth habit of Sphagnum is directly responsible for the development of one of nature’s most efficient carbon traps. A metre squared of intact, good quality raised bog sequesters a small amount of carbon annually, but over time these peatlands can accumulate and store much more carbon than the same area of other ecosystems like tropical rainforest. As such, Sphagnum moss is very important to help tackle climate change by taking in carbon and by creating peat-forming conditions to secure this carbon in the ground within healthy peatlands.
The ability of Sphagnum to store water also plays an important role in regulating heavy rainfall events within a catchment. Healthy peatlands can store water in Sphagnum moss, then slowly release this water over time, thereby helping to mitigate potential downstream impacts associated with sudden heavy rainfall.
Sphagnum as an indicator species
Different Sphagnum species can be used as valuable indicators of peatland type and their overall condition. However, Sphagnum mosses are widely believed to be tricky to identify and so many ecologists simply aggregate them, classifying them as “Sphagnum species”. In doing so, ecologists are forfeiting valuable information on nutrient availability, hydrology and habitat condition that these species provide. Like any other plant group, there are generalist and specialist Sphagnum species. For example, Sphagnum rubellum can be found on nearly any bog habitat in Ireland. Small red cushions and hummocks can be found from relatively dry cutover bog to the wettest parts of an active raised bog.
Sphagnum beothuk has a very characteristic chocolate brown colouring and is one of the prettiest raised bog species. While S. austinii has a range of colours, the large size of the individual capitulums (the top of the plant) and the relative compactness of the hummocks as a whole can be used to reliably identify the species. Both species generally inhabit the wetter parts of a bog and if abundant and healthy, can be used as an indicator of raised bogs in good condition. Sphagnum cuspidatum is one of the most aquatic species and is generally found in the acidic bog pools in the wettest parts of the bog. Interestingly, it can be found within the drainage ditches of industrially harvested bogs where no other Sphagnum species may be present. There are some Sphagnum mosses that are found in less acidic and more nutrient rich, fen conditions. To get to know Sphagnum species is to open a large encyclopaedia on the various natural history processes and conditions of our peatlands. However, don’t be put off getting to know the more readily identifiable species and build on this. Knowing just a few species can really add to the satisfaction of exploring our unique peatlands.
Use of Sphagnum moss in peatland restoration
Planting Sphagnum moss across re-wetted cutaway bog as a rehabilitation technique is a key objective of the Peatlands and People LIFE Integrated Project (IP). We’re on track to plant one million Sphagnum plugs across over 270 hectares of rehabilitated peatland by November 2024, with ambitious plans for further planting in 2025 and beyond.
Revegetating these areas provides new and more resilient habitat over the longer term. Sphagnum moss will recolonise these sites naturally in time; however, the work we’re doing aims to speed up this trajectory, and we’re establishing a network of peatland sites to develop best practices in restoration and rehabilitation. This involves the design of robust methodologies to monitor and analyse Sphagnum and carbon storage.
While monitoring is ongoing and we have a lot of research ahead of us, initial evaluations of the planted Sphagnum material is already showing positive survival and growth rates.
As I continue my work with Bord na Móna, we’re grateful for the support provided by the European Union’s Recovery and Resilience Facility as part of Ireland’s National Recovery and Resilience Plan, a key instrument at the heart of NextGenerationEU. The primary aim of this scheme is to optimize climate action benefits of rewetting the former industrial peat production areas by creating soggy peatland conditions that will allow compatible peatland habitats to redevelop.
David McNicholas is an Ecologist at Bord na Móna where he works with a multidisciplinary team to deliver an ambitious peatland restoration programme, post-industrial peat production. As a member of the Bord na Móna Ecology Team, David is involved in rehabilitation planning and implementation, while also planning and undertaking monitoring and protected species surveys.
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