A Burning Issue: Assessing the impact of alternative grouse moor managements on vegetation dynamics and carbon cycling on UK blanket bogs

Blanket bogs are a globally rare habitat and store vast quantities of carbon in the form of peat. In the UK, blanket bogs are subject to a variety of anthropogenic activities which threaten their ability to maintain this carbon store long term. Release of this carbon is likely to exacerbate climate change. Burning peatlands to encourage Calluna vulgaris on grouse moors is thought to be detrimental to peat-forming vegetation, water quality and the peatland carbon balance but lacks robust evidence. This study aimed to assess the effects of different methods of Calluna management on the carbon balance, vegetation dynamics and water quality of blanket bogs. A paired catchment manipulation was combined with plot-scale manipulations and replicated across three English blanket bogs managed as grouse moors to examine the effects of burning, mowing, no management and variations thereof on the carbon balance and vegetation changes. Carbon balances indicated that unmanaged areas were a carbon sink whereas both burning and mowing caused carbon release. Taking the quantities of burnt plant biomass and tractor fuel into account, burnt areas were a stronger carbon source than mown areas. Mowing increased both height and cover of Calluna compared to burning, promoted growth of Eriophorum vaginatum, a peat-forming species, and had less bare ground. The nutritional content of Calluna increased under management, being slightly higher following burning than mowing. A pot experiment was combined with radiocarbon analysis to explore whether Calluna-associated ericoid fungi break down recalcitrant matter in the peat. The radiocarbon dates strongly indicated that ericoid fungi decomposed recalcitrant ancient compounds within the peat, releasing these as gaseous and aquatic carbon. Altering Calluna management practices by replacing burning with mowing, where feasible, could potentially bring benefits for the peatland carbon balance and water quality by increasing abundance of peat-forming species without negatively impacting upon grouse.