Peatlands in the UK were formed about 6000–8000 years ago following the end of the last ice age. Due to the cold and wet conditions, organic matter input from vegetation does not decompose completely and so peat is formed. This peat has accumulated to a depth of about 2-3 metres, covering much of the UK uplands in a “peat blanket”.
Globally, peatlands occupy only 3% of the global land area, but contain about a quarter of the carbon that is stored in soils – twice the amount of carbon stored in all the world’s forests. However, peat carbon stores are vulnerable to climate change and insensitive management, which disrupts the peat hydrology and increases the rate of decomposition, ultimately degrades the peatland. Instead of absorbing carbon from the atmosphere and effectively mitigating against climate change, degraded peatlands often release carbon and thus exacerbate climate warming. In addition, wet peatlands can also release large amounts of methane, a potent greenhouse gas and large contributor to climate change.
Restoring and improving the carbon storage potential of peatlands helps to mitigate climate change. However, current global models do not yet fully account for the peatland carbon cycle and its potential feedbacks on global climate via altering atmospheric carbon dioxide and methane concentrations.
For example, in the UK, there are knowledge gaps on how the carbon cycle of heather-dominated upland blanket bogs responds to climate change and how management techniques, such as prescribed vegetation burning or alternative cutting could help support peatland resilience to climate change impacts.
We particularly need to understand more about the impacts of management on soil organisms affecting peat carbon storage, decomposition rates and methane emissions to maximize peatlands’ climate benefits from management. We also need to understand more about how to restore historically degraded peatlands, such as those that have been drained for farmland or recreate those lost due peat cutting for fuel.
Over the last 20 years, SEI has measured peatland carbon cycling in the UK to understand how much carbon is taken up by vegetation and stored long-term in the soil and how much is lost to the atmosphere via decomposition of organic matter. Having a better understanding of these processes is of key importance for global models in order to understand terrestrial ecosystem carbon dynamics and future atmospheric carbon concentrations, and thus climate change.
This research is led by Andreas Heinemeyer, Senior Research Associate at SEI York based at the University of York. Over the past 10 years, the Peatland-ES-UK project has focused on blanket bog peatlands in northern England, specifically how different land management practices can lead to different impacts on biodiversity, carbon storage and greenhouse gas emissions, especially methane.
The overall aim of the project is to deliver robust and long-term experimental evidence to assess the impact of restoration management techniques on heather-dominated blanket bog, such as prescribed vegetation burning and mowing. This is to ensure the peatland ecosystem can function sustainably, including in its role in carbon storage.
The UK Department for Environment, Farming and Rural Affairs-funded project “Restoration of blanket bog vegetation for biodiversity, carbon sequestration and water regulation” ran from 2012–2016 and was initiated to address many of the current knowledge gaps, particularly around comparing the impacts of management techniques including burning, mowing or leaving vegetation uncut. The project took a holistic research approach by considering a wide range of interconnected aspects around carbon, water and biodiversity, including impacts far beyond the peatlands. Over five years, a range of field experiments were conducted to investigate these impacts at the plot and catchment scale.
One research outcome showed that for burning, carbon losses were initially higher due to vegetation combustion, but soil decomposition rates subsequently decreased and vegetation carbon uptake increased, reducing the impact of the initial loss of carbon over time. Accordingly, burning could have an overall positive impact on the carbon storage of the peatland.
It was also found that after mowing, annual carbon losses from brash (leftover material) decomposition were lower. However, ongoing brash decomposition continues to release carbon over the long-term. Mowing may therefore have a less positive impact on the carbon storage of peatlands than prescribed vegetation burning. This means that whilst both management regimes (burning and mowing) caused an initial switch from a net carbon sink to a source, the overall net impact is uncertain and requires further measurement.
Moreover, the study found that methane emissions decreased after burning due to slightly reduced water tables, whilst methane emissions were higher after mowing, having higher water tables (i.e. wetter peat).
Peat core samples revealed the potential positive impact of charcoal from vegetation burning on long-term carbon storage and the need to include this aspect in measurements and models when assessing net peatland carbon balance management impacts.
Other management issues were investigated, such as physical impact from heavy machinery used for large-scale heather cutting and reducing peat surface topography that is crucial for habitat diversity.
As important as these findings are, they are only initial results. In order to fully understand implications across whole catchments, especially on the cumulative carbon balance over time, longer-term studies are required. The project has received a further five years of funding from a consortium of funders representing major stakeholders.
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