Mosses and other peat bog vegetation remove carbon dioxide from the air in the same way as trees – but when the vegetation dies, a proportion of it becomes waterlogged – oxygen is excluded, it cannot rot, and so no carbon dioxide is released. As long as the peat remains waterlogged – i.e. in a bog – then the carbon stored within it will remain there indefinitely. However, when a bog has been drained or vegetation overlaying peat has been eroded typically by trampling and grazing by too many livestock or deer then the peat becomes exposed to air, and carbon dioxide is released. Consequently, keeping peat bogs healthy and wet is a key aspect of sustainable land use management within the wider strategy of combating climate change
The concept of carbon capture – removing carbon dioxide from the atmosphere and locking it away long-term so it cannot heat the Earth further – is commonly associated with planting trees.
But a healthy peat bog has the capacity to store much more carbon dioxide than a similar area of woodland because the organic matter accumulates over thousands of years. Within our nationwide land holding, the National Trust for Scotland has extensive woodland and peat bog cover, and we therefore have an important role to play in conserving this key element of our Natural Capital.
Since we look after so much peat bog and woodland, the Trust has an important role to play in storing carbon. The place of woodland in annual carbon retention has been understood for some time. We know that, on balance trees absorb more CO2 from the atmosphere than they release through respiration and decomposition. The Forestry Commission has developed look-up tables to estimate carbon stocks in woodlands of different ages. Woodland captures carbon from the atmosphere at a much faster rate than peat bog vegetation – typically 10-25 times faster. However, natural or near natural peat bogs store a much greater quantity of carbon per hectare of land, as a result of the accumulation of organic matter over thousands of years.
The Trust owns 76,000 hectares of land across Scotland, the majority in the uplands which contains significant peat deposits. We are focusing on measuring the peatlands and their associated carbon store – and identifying where there is scope to restore degraded peat bogs. The Trust has also adopted a policy to phase out the use of horticultural peat within its garden properties.
In 2013 the Trust assessed the total peat coverage on most of its upland properties, using satellite imagery, GIS maps and ground surveys. The total estimated area of peat soils was 16,000 hectares. Based on an assumed average peat depth of 1m, the total volume of peat was estimated to be 160 million cubic metres (m3). Using the generally accepted figure of 172kg of CO2eq per m3 of peat, the total store of carbon on National Trust for Scotland upland properties can be estimated as 27.5 million tonnes CO2eq (carbon dioxide equivalent). This is about a third of the annual greenhouse gas emissions in Scotland. The equivalent figure for NTS woodland (which extends to around 5,045ha) is 2.4 million tonnes CO2eq11. Further unquantified stores of carbon are held in the Trust’s arable and grazing lands.
* Carbon storage can be measured as tonnes of Carbon (C) or tonnes of Carbon Dioxide equivalent (CO2 eq) where 1 t C = 3.67 t CO2 eq. Mt = million tonnes.
The map below shows the proportional estimated stores of carbon in peat and woodland at the 14 upland properties with the largest peat stores (based on an average peat depth of 1m). These are conservative estimates, as surveys on Ben Lawers, Ben Lomond and Goatfell in 2014–15 found deeper layers of peat.
Ben Lomond is estimated to have 330ha of drained peat, more than any other NTS property, and much of this is on steeply sloping ground. Experience elsewhere in the UK has shown that blocking drains on steep ground (more than 6o) is problematic, and so the primary objective of the project undertaken in 2014–15 was to trial two methods of blocking drainage ditches on different areas of the steeply sloping peatland. A detailed assessment of the functional condition of the peat bog was carried out after the restoration work.
We think that the restoration works will, in total, save around 877tCO2eq over 50 years, or 17.5tCO2eq per year. This is equivalent to the yearly emissions of 3.4 medium-size diesel cars doing an average of 18,100 miles per year. Not only are these very significant results in terms of carbon budgets, but the restoration method of blocking drainage ditches was also shown to be highly cost-effective, at around £3,000 per hectare.
The major problem identified on Ben Lawers was the presence of large areas of eroded peat, possibly caused by a combination of (a) trampling by sheep or deer and (b) wind erosion. In some areas this has resulted in flat areas of exposed peat; in others peat haggs (vertical banks of peat – see photo below) have developed. The extent of bare disturbed ground is a contributory factor to the unfavourable condition of the peatland habitat in the Special Area of Conservation.
The project aimed to protect the peatland in two areas from further erosion by (i) re-profiling the haggs and (ii) restoring vegetation, trialling different techniques such as planting, mulching and application of protective sheets of compostable material (geotextiles). The project was designed to compare the restoration of peatland in Coire Odhar – where there is grazing, although at a lower density than on the rest of the hill – with that on the southern slopes of Meall nan Tarmachan, which is protected from grazing by fencing.
While it is too early to reach detailed conclusions on the trials, the digger re-profiling was found to be very effective. The total area restored across the Ben Lawers sites was around 0.5ha, and restoration costs equate to approximately £40,000 per hectare – but the benefit is substantial. As shown in the table on pages 10-11, the net effect of restoring ‘actively eroding’ peatland to ‘drained’ or ‘modified’ condition is to cut emissions by some 20 tonnes CO2eq per hectare per year. The Ben Lawers project could cut emissions by around 10 tonnes CO2eq annually – an amount similar to the yearly emissions of two diesel cars.
Work undertaken in 2014–15 on the Trust’s Goatfell property on the Isle of Arran extended the area of previous restoration work on two drained blanket peat sites.
The first site is an area of upland blanket bog west of the summit of Maol Donn (between 320m and 350m above sea level) that had been degraded by drainage channels. Part of this site had previously been repaired using peat dams. The project (a) extended the restored area and (b) reinforced some of the existing peat dams with plastic pilings where the flow of water had caused the dams to fail.
The second site is an upland blanket bog at Coire a’Bhradhain on the east side of the burn below Cnoc Breac (between 340m and 380m above sea level), also degraded by drains. Just under 3 hectares had been restored using plastic pilings, and the project extended this area using peat dams. A team of volunteers helped to install the plastic pilings to reinforce eroded peat dams and to strengthen some of the new dams (where the ditches were very wide but with a good depth of peat). This also enabled us to explain the importance of functioning upland bogs to a wider audience.
As a conservation charity, part of the Trust’s core purpose is to promote and protect the natural environment, especially through the management of its properties.
Our Climate Change Action Plan for 2013–17 focuses on carbon accounting. Restoration and protection of peatlands lies within the action area of ‘management of land and ecosystems with consideration for climate change’, for which we have set ourselves three key tasks:
The Trust’s climate change reporting shows that we currently emit about 5,000 tonnes CO2eq per year. This compares with an annual CO2eq removal of 14,667 tonnes CO2eq by peat and 42,379 tonnes CO2eq by woodland. Our annual carbon capture outweighs our carbon emissions by a ratio of 11:1. Nevertheless, the Trust is still strongly committed to reducing its carbon emissions and contributing to the Government’s carbon-reduction targets.
It is clear that by changing our land management practices to enhance carbon storage – for example, by restoring bogs or increasing our woodland on mineral soils – we can have a major effect on our overall carbon balance, and this can be implemented very cost-effectively.
As a leading conservation body and owner of upland properties across Scotland, the National Trust for Scotland – with appropriate levels of investment and an enthusiastic volunteer resource – has the potential to positively shape the environmental heritage which will be passed to future generations.