Peatland vegetation change and establishment of re-introduced Sphagnum moss after prescribed burning

Fire, including prescribed burning, is common on peatlands globally and can affect vegetation, including peat-forming Sphagnum mosses, and affect ecosystem services. We monitored vegetation in different burn-age categories at three UK peatland sites over a 19-month period. Half of the plots had Sphagnum fragments added and their survival was assessed. Changes in vegetation composition over time, and associations between vegetation composition, site and burn-age category were investigated. Plots in the most recently burned category were likely to have more bare peat, a thinner moss layer and lower vascular plant strata. Graminoid cover initially increased after burning but was low after 10 + years. Dwarf shrub cover increased after burning and remained high after 10 + years. At the most Sphagnum-rich site, a high proportion of existing Sphagnum cover was bleached one year after burning, but recovery occurred during the study period. Sphagnum re-introduction success decreased over the study period in the most recent and intermediate burn-age categories at the most Sphagnum-poor site. These results show that burning rotation length is an important factor in determining site-level vegetation composition on burned sites. More frequent burning will result in a greater proportion of land in the early post-burning stages, potentially resulting in a thinner moss layer, more bare peat and less healthy Sphagnum, with potential consequences for carbon balance. No evidence was found to support the use of burning as a tool to increase existing Sphagnum or promote Sphagnum re-establishment success.