Fire temperatures and Sphagnum damage during prescribed burning on peatlands

Prescribed burning affects plant community composition including the abundance of peat-forming Sphagnum mosses. Understanding the processes by which fire impacts occur and the variability of impacts according to fire severity is important when making fire management decisions. We monitored fire temperatures and their impact on Sphagnum capillifolium in 16 experimental fires in the field. Cell damage in response to high temperature exposure in the laboratory was also quantified for five different Sphagnum species (S. capillifolium, S. papillosum, S. magellanicum, S. austinii and S. angustifolium). Maximum temperatures recorded at the moss surface during fire ranged from 33 °C to 538 °C and were higher in plots with greater dwarf shrub cover. Higher temperatures were associated with a greater proportion of cell damage in S. capillifolium, with 93–100% cell damage observed 10 weeks after burning in the upper parts of plants exposed to temperatures over 400 °C. All five species tested in the laboratory experiment also showed more damage at higher temperatures, with damage occurring immediately after heat exposure. These results indicate that hotter fires are likely to have a greater impact on Sphagnum survival and growth, and could slow the rate at which the peatland moss layer sequesters carbon.