Peat Moss
(Sphagnum SP.)
Sphagnum papillosum plant structure and water being squeezed from a clump of Sphagnum (below) (Photos: North Pennines AONB Partnership)
Description
Sphagnum is a genus of specialist mosses found in waterlogged, acidic and nutrient-poor conditions such as those in bog ecosystems. There are around 30 different species of Sphagnum moss in the UK varying in colour and size, but all have the same long, branched structure featuring stem leaves and a round capitula, or head, at the top. Most of the structure of a Sphagnum plant is below the ground surface, with only the capitula and top few centimetres visible.
Peat moss is not quickly broken down due to certain components (phenols) in the cell walls. After centuries, the slowly humified old Sphagnum forms the well-known Sphagnum peat. This peat used to be excavated on a large scale for fuel but is now mainly used by the growing substrate industry (including potting soil).
Different Sphagnum moss species grow in different environments, some forming carpets, tussocks or covering the surface of pools. Species vary from common to extremely rare, and all have different characteristics. The species of Sphagnum you are most likely to see in the north of England are Sphagnum fallax, S. papillosum, S. capillifolium and S. palustre.
Sphagnum is a crucial feature of bog ecosystems as it is the primary peat-forming plant, without which the peat forming process and the ecosystem services that result from it, such as carbon sequestration, cannot occur. Sphagnum mosses alter the conditions of their environment, lowering the pH and making it more suitable for other characteristic bog plants to colonise. Sphagnum also has an extremely high water-holding capacity, holding up two twenty times its own weight in water. This contributes significantly to peatlands’ ability to store water, acting as sponges in the landscape during periods of high rainfall by absorbing excess water and releasing it more slowly into watercourses, reducing the risk of downstream flooding.
Sphagnum capillifolium
(Photo: North Pennines AONB Partnership)
Sphagnum cuspidatum
(Photo: North Pennines AONB Partnership)
Sphagnum fallax and palustre
(Photo: North Pennines AONB Partnership)
establishment & maintenance
Sphagnum mosses can be added to the wetter areas of sites to help retain water and prevent bare peat from drying out. Sphagnum moss establishment in bog grasslands can be achieved in different forms. It can be introduced as clumps, plugs, pellets, beads, fragments, gel or slime, whereas clumps, plugs and pellets are the most commonly used techniques. After removing the nutrient rich topsoil, a density of 75 – 100 m3 of moss per hectare is already enough to establish a full moss cover (Quinty & Rochefort, 2003). To keep the water table stable at a few centimetres below the surface, surface should be levelled and ditches should be dug at 10-meter intervals. An electric pump and overflow facilities can be used to maintain the water level. In the case of flooded bogs, floating mats of moss can be used to establish sufficient coverage (Gaudig et al., 2017).
Reintroducing Sphagnum to degraded peatlands from which it is absent or scarce is a relatively new area of peatland restoration with limited existing research. Sphagnum inoculation is usually carried out as the final step in restoration to increase the speed at which Sphagnum mosses and other moorland plants revegetate bare areas. There are a variety of techniques used for doing so, all with varying advantages and disadvantages, as shown by the table below.
Table 1: Inoculation technique comparison
Using clumps from donor sites must be done carefully to ensure the impact is minimal. Clumps are harvested by hand; a handful of moss is removed, and the remaining moss is roughly knitted back together. Generally, clumps are harvested at a maximum rate of one per four square metres, no more than 10 % of an area of Sphagnum is taken and clumps are always taken from the edge of hummocks rather than the centre.
Before ...
(Photo: North Pennines AONB Partnership)
... and after clump harvesting
(Photo: North Pennines AONB Partnership)
As yet, comparison between the efficacy of these techniques is largely anecdotal, as is their impact on restoration and donor sites. As part of the Pennine PeatLIFE project, trials are underway on restoration sites across the North Pennines Area of Outstanding Natural Beauty (AONB), Yorkshire Dales and Forest of Bowland AONB. In trial plots, each Sphagnum inoculation technique is applied and monitored annually to find out which is the most effective. Donor areas from which clumps have been harvested are also closely monitored to assess the impact that harvesting has on healthy peatlands. The results of these trials will be shared with other peatland restoration organisations and used to inform future restoration decisions to maximise the efficacy of our work.
Trial plots on a bare peat pan (Photo: North Pennines AONB Partnership)
harvesting & yields
After 3-4 years the peatmoss can be harvested for the first time, and after that every 3-5 years. On cut over bogs and former bog grasslands the yield reaches 3-6 t DM ha-1 per year. For floating mats, the yield reaches 2-4 t DM ha-1 per year (Gaudig et al., 2014).
The lack of highly specialized harvesting machinery forces harvesting to take place using an excavator when the soil is either relatively dry (Summer) or frozen (winter). Different harvest times may influence biomass quality and add impurities in the biomass due to inclusion of other moss species (Gaudig et al., 2017). Further investigation needs to be conducted to determine the ideal moment for harvesting and minimize impurities.
ecosystem services
Apart from the income generated by the biomass production, carbon credits can provide an additional source of income for Sphagnum farming. Net GHG emissions from Sphagnum faming are close to zero and 27-37 t CO2e less per ha than former drained bogs (Bianchi et al., 2021). If a comparison is made to conventional drained agriculture with livestock that includes farmyard emissions (51 t CO2e per ha), the GHG emission decrease can be even larger (Liu et al., 2023).
Sphagnum farming conserves existing peat and can rebuild the lost peat on formerly drained soils, while simultaneously functioning as a water retention basin, increasing flood resistance. On op of that, peatmoss systems harbour multiple rare species including, plants, spiders, and rare slime moulds (Wichmann et al., 2012). With harvesting in long rotational cycles, different succession stages of the peatmoss system are maintained, supporting a wide variety of species (Muster et al., 2015). If a credit scheme for these ecosystem services is further developed, this can add extra income to Sphagnum farming making it more economically viable (More info on credit schemes here).
Applications
Growing Substrate
As a paludiculture crop, Sphagnum can be used as an ingredient for high quality growing substrate. The physical and chemical properties of peatmoss biomass are very similar to that of slightly decomposed fossil peat that is now mainly used for growing substrate and potting soil. Since the market for this product already exists, all the necessary infrastructure is present. For a more detailed market outlook and an economic analysis, click here
Ornamental Material
Sphagnum moss is used as decoration material in flower arrangements. Demand for this material peaks around Christmas and Easter, when flower arrangements are in full demand. Criteria for this application are the water retention capacity and colour. A fresh green color is preferred to a grey colour.
Nature Restoration
With Sphagnum being an important species in the restoration of wetlands and native biodiversity, live peat moss is used to restore excavated and degraded peat areas. With increased awareness of the importance of wetland restoration as well as an increase in regenerative farming, the demand for live peatmoss will only increase. Click here for an example of wetland restoration using peat moss in the UK.