The effects of fire on peatland carbon stocks and dynamics

Between 15 and 17 April 2007, a human-induced fire disturbed around 55 km2 of the Galloway Forest Park in southwest Scotland. The burn area included the Silver Flowe National Nature Reserve, a large blanket bog which has a great diversity of vegetation and hummock-hollow patterning. This event provides an unprecedented opportunity to investigate the immediate impacts of fire on peatland carbon stocks, as well as the longer-term changes in peat physical structure, vegetation and below-ground (decomposer) communities that occur after fire. Globally peatlands store a huge amount of carbon as soil organic matter (peat). Over the next decades, fire frequency in peatland-dominated regions is likely to increase as a result of human-induced global warming. By burning the peat, fire can release carbon stocks to the atmosphere as 'greenhouse gases', possibly amplifying global warming further. Conversely, fire can also lead to thermal alteration ('charring') of peat, converting it to a form which is highly resistant to decomposition and therefore protected from release to the atmosphere. Over the longer term, post-fire changes in surface characteristics (soil physical properties, water chemistry, vegetation, decomposer communities) may either increase or decrease the ability of peatlands to store carbon. The overall aim of this study is to improve our understanding of how peatland characteristics mediate the direct impact of fire on carbon stocks, as well as longer-term recovery of carbon-storing ability. We will assess the immediate impact of fire by quantifying the amount of organic matter lost by direct combustion and the amount 'charred' or thermally altered. To do this, we will collect short (50 cm) cores from a range of vegetation types and topographic features that were burned, and then analyse burned and unburned sections of the cores using a range of chemical methods. We predict that areas with large open water pools will be protected from fire impacts, whereas areas dominated by mosses that dry out during droughts will be affected most severely. To enable long-term monitoring of post-fire recovery, we will set up permanent sampling stations across a range of vegetation types and topographic features, in both burned and unburned (control) sites. At each sampling station, we will install equipment that automatically records soil temperature and water-table level. At three times over the year, we will take samples for water chemistry and record changes in vegetation; samples will also be collected for analysis of below-ground decomposers (bacteria and fungi). Together, these data will give us a picture of how the peatland surface changes, both physically and biologically, after fire. Sampling will begin in the first growing season post-fire (i.e., summer 2007). Further funding will be sought at a later date to allow continuation of long-term monitoring and to investigate specific mechanisms of impact and recovery.