- Peatlands are the UK’s largest carbon store, and include many agricultural areas, near-natural peatlands and upland moorland.
- In general, pristine peatlands are around carbon neutral, whereas those modified by humans tend to release carbon and account for 4% of the UK’s greenhouse gas emissions.
- Over 90% of these emissions come from lowland peatland.
- Grouse moors store around 11-35% of England’s total peatland carbon but emit only around 1-5% of total peatland carbon emissions.
- Managed heather burning releases a small amount of carbon, but carbon is then taken up with regrowth, and the reduction in fuel available means that it may reduce the risk of more damaging wildfires.
- The science on carbon flow in the uplands is complex and ongoing, for example with the role of biochar recently being investigated for the first time.
Carbon storage and release in peatlands: sink or source?
In this second briefing sheet, we focus on the critical issue of carbon storage, and its release to the atmosphere. This is highly relevant as peatlands are the UK’s largest carbon store, covering 11% of England’s land area and estimated to store around 584 million tonnes of carbon. Peatlands are found across a wide variety of environments, including upland moors, bogs, grasslands and fens. Lowland peat habitats are often used for farming.
Carbon cycles in and out of these natural carbon stores in various ways. For example, carbon dioxide gas (CO2) is taken up by growing plants, and dissolved carbon dioxide may be brought in within rainfall. Both CO2 and methane gases are released from the peat if dead or damaged plants decompose, as well as carbon itself and other carbon compounds escaping peatlands either dissolved in water or as particles. Carbon loss can be accelerated by certain events, such as dry periods or fire leading to drying of peat, and carbon capture can be encouraged by restoration, when peat starts forming again.
Greenhouse gas emissions from our peatlands as a whole make up 4% or the UK’s total. Of these, those that are pristine, or near-natural, are thought of as fairly carbon-neutral – they hold on to their store of carbon and do not release it. However, those that are modified by or managed by humans usually release carbon, but the amount of carbon being released into the atmosphere from different kinds of peatlands varies widely.
In general, those that are modified by drainage, cutting, burning or erosion are relatively low carbon sources, emitting between around two and five tonnes of CO2 equivalent (CO2e) per hectare per year. Peatlands managed for cropland, grassland, forestry (for example afforestation of moorland) or fuel harvesting emit many time more at around eight to 39 tonnes CO2e per hectare per year.
Grouse moors and carbon
Carbon in the uplands
It is estimated that England’s total upland peat area emits around 603,000 tonnes of CO2e per year, which is 5.6% of the total peatland greenhouse gas emissions in England. The remaining 94% of England’s peatland emissions come from lowland peat.
Carbon on grouse moors
Peatland under grouse moor management represents only a portion of this upland peat. Using data from the Moorland Association, recent GWCT estimates put the amount of carbon stored in peat on grouse moors at between 66 and 205 million tonnes, which is 11-35% of the total carbon stored all English peatlands. We went on to estimate carbon emissions from grouse moors and found that English grouse moors emit around 1-5% of the net carbon emissions from England’s peatlands per year. English grouse moor carbon emissions are therefore proportionally well below the proportion of carbon that they store, compared to other peatland uses.
These figures are helpful in contextualising various peatland emissions, but the important point is that the UK’s peatlands are a large and precious store of carbon. There is enormous potential for carbon savings by prioritising the areas with most potential and we need to understand how best to manage them.
What is it?
On grouse moors and some other peatland environments, vegetation can be managed by prescribed burning, in accordance with the heather burning code. This is a rapid, cool burn of small strips of heather that removes the old, woody vegetation but does not penetrate down into the peat itself. Managed heather burning is often misrepresented in the media as “peat burning”, but the aim of moorland managers is to remove only the old vegetation and allow the plants to regenerate, often not even affecting the litter layer beneath the heather, and certainly avoiding peat ignition.
Heather burning and carbon
When heather is burnt as part of a managed burning programme, some carbon is released during the burn. However, carbon is then captured by the regrowing vegetation afterwards. How you assess carbon capture/release on areas that are managed by burning depends on when you measure it in relation to time of burning. Studies looking at long-term carbon cycles on upland peatlands are very limited, and the science that is available has tended to focus on a few sites that have been intensively studied. This is a well-known limitation of the scientific evidence in this area.
When comparing peatland managed with burning to unburned areas, many studies find that there are short-term losses of above ground carbon from the burnt vegetation, but that this is stored again in vigorous regrowth in subsequent years. The science does not yet confirm whether the losses in smoke are cancelled out by vegetation re-growth. Many studies that have been conducted are short-term, carried out in the year of the burn or the few years thereafter, whereas for a full understanding of the carbon balance studies are needed that span much longer periods – for example perhaps 15 years of a burning cycle.
How much do we know?
Science in this area is progressing all the time. For example, one recent York University study began to investigate for the first time the role of pyrogenic charcoal – also known as char, black carbon or biochar – this is produced when vegetation is burnt, and can store large amounts of carbon for a very long time. The study found a positive relationship between managed burning frequency and the amount of carbon stored, meaning that where heather was managed with cool burns, more carbon was stored. Previous studies have not included charcoal in their calculations, but it may play an important and previously unknown role.
Every carbon stock study so far has found positive carbon and peat accumulation within flat and wet areas of blanket bog, whether managed by burning or not. In general, areas managed with a ten year burning cycle seem to accumulate less carbon than those that were not burnt recently, but a recent study found similar carbon storage rates between areas burnt on a 20 year rotation compared to plots unburnt since 1954 or 1923. Two further studies have found that recently burnt areas emitted less carbon than older burn or no burn plots. Clearly more work is needed to understand this complex subject, and it is an area of active research. Although carbon is released with heather burning, the authors of a recent study concluded that careful burning management at that site did not have a major detrimental effect on the overall carbon budget for the moor. The simple narrative that is sometimes heard that managed heather burning causes huge carbon losses is not supported by the science.
Although there are known limited losses of carbon associated with prescribed burning, the subsequent reduced fuel load may lower the risk of wildfire, which carries a much greater chance of huge carbon releases. In many places worldwide, managed burning is used as a tool to remove the build-up of fuel so that wildfire is less likely to occur or take hold. Although there is very little evidence on this from the UK, lessons can be learnt from wildfire management in areas such as Australia and the USA, especially in the light of climate change potentially leading to increased temperatures, drier peat and higher wildfire risk.
Managed heather burning is carried out in winter, when the ground is wet. Most of the damaging wildfires that have been seen on moorland in recent years have occurred in summer, when managed heather burning is not taking place, and in some cases (for example Saddleworth Moor) on areas that are run with a no-burn policy towards heather management, resulting in greater fuel load. These wildfires can lead to devastating losses of carbon, with many centimetres of peat burning and releasing their stored carbon that will take many years or even centuries to reform.
The concept of blanket bog restoration burning has been created recently, where burning is used to reduce heather dominance and create conditions more favourable for good peat-forming plants. The recognition that well-managed heather burning can play this role is helpful. Burning should be for wider ecological purposes, rather than carried out solely on a strict time frame as is sometimes dictated in agency management instructions. The concept of restoration burning has allowed a common middle ground where practitioners assess and manage the land to benefit blanket bog condition and associated vegetation. Some commentators promote the idea that all burning is the same and make no distinction between managed/prescribed/cool burns and wildfires. This is a common mistake, but one which is easily avoided for the well-informed.
It is critical that we better understand the role of burning for heather management and how it relates to carbon storage, peatland condition and wildfire prevention/mitigation before making changes that may have damaging and long-lasting effects.
This briefing sheet draws on information from the GWCT’s 2020 Peatland Report, which is fully referenced and available here.
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