Abstract
Peatlands are globally important carbon stores, yet both natural and human impacts can influence peatland carbon accumulation. While changes in climate can alter peatland water tables leading to changes in peat decomposition, managed burning of vegetation has also been claimed to reduce peat accumulation. Particularly in the UK, blanket bog peatlands are rotationally burned to encourage heather re‐growth on grouse shooting estates. However, the evidence of burning impacts on peat carbon stocks is very limited and contradictory. We assessed peat carbon accumulation over the last few hundred years in peat cores from three UK blanket bog sites under rotational grouse moor burn management. High resolution (0.5 cm) peat core analysis included dating based on spheroidal carbonaceous particles, determining fire frequency based on macro‐charcoal counts and assessing peat properties such as carbon content and bulk density. All sites showed considerable net carbon accumulation during active grouse moor management periods. Averaged over the three sites, burns were more frequent, and carbon accumulation rates were also higher, over the period since 1950 than in the period 1700–1950. Carbon accumulation rates during the periods 1950–2015 and 1700–1850 were greater on the most frequently burnt site, which was linked to bulk density and carbon accumulation rates showing a positive relationship with charcoal abundance. Charcoal input from burning was identified as a potentially crucial component in explaining reported differences in burning impacts on peat carbon accumulation, as assessed by carbon fluxes or stocks. Both direct and indirect charcoal impacts on decomposition processes are discussed to be important factors, namely charcoal production converting otherwise decomposable carbon into an inert carbon pool, increasing peat bulk density, altering peat moisture and possibly negative impacts on soil microbial activity. This study highlights the value of peat core records in understanding management impacts on peat accumulation and carbon storage in peatlands.
Highlights
HEINEMEYER ET AL.Globally, peatlands contain around 30% of all soil organic carbon (SOC), despite covering only 3% of the land surface (Parish et al, 2008)
The cohorts provide an archive of peatland development alongside pollution traces used for dating such as spheroidal carbonaceous particles (SCPs) that can be used to reconstruct past vegetation, climate conditions and peatland events such as fires over time, providing key information on how peatlands respond to changes in climate and management
There was a peak in bulk density (BD) of around 0.15– 0.2 g/cm3 at a depth of about 5 cm, which coincided with the highest peak in SCPs at all sites
Summary
HEINEMEYER ET AL.Globally, peatlands contain around 30% of all soil organic carbon (SOC), despite covering only 3% of the land surface (Parish et al, 2008). In the northern hemisphere circumpolar region it is the generally low temperatures, high water‐table depth, high peat moisture, and the resulting slow decay rates of net primary production (NPP) which allow peat to form This slow decay with very limited soil mixing (no meaningful bioturbation or cryoturbation, apart from in permafrost soils) results in annual peat cohorts. A better process‐level understanding of climate (e.g., Davidson & Janssens, 2006) and management (e.g., Evans et al, 2014) impacts on peatland SOC cycling is clearly needed since the mineralisation of peatland soil organic matter (SOM) has the potential to release vast amounts of previously locked‐up C into the atmosphere (as outlined in Heinemeyer et al, 2010; e.g., Yu et al, 2001)
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