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Peatlands are internationally important ecosystems, and play a vital role in carbon sequestration, water provision and global biodiversity. Fire occurs on peatlands worldwide and includes prescribed burning for purposes including agriculture and wildfire control. Many UK blanket peatlands are subject to prescribed burning to encourage production of the game bird red grouse (Lagopus lagopus scotica), but such burning may not be compatible with environmental outcomes related to carbon, water and biodiversity. Vegetation plays a key role in peatland ecosystem services, so evidence of how fire affects vegetation is needed to inform decisions about the future of prescribed burning. The work in this thesis considers vegetation change in the years following prescribed burning, with a focus on peat-forming Sphagnum mosses. A range of approaches including field monitoring and laboratory experiments were used to investigate the key plant taxa affected, timescales of change, and processes responsible for fire impacts. Important findings include differences in vegetation composition between burned and unburned plots on national and regional scales. Evidence of negative impacts of burning on Sphagnum mosses was found, with lower cover on recently burned plots on a national scale, reduced growth in response to fire-induced changes to peat properties, and increased cell damage after high temperature exposure, although ash addition increased growth. Data from a long-running field experiment revealed that fire impacts on Sphagnum can persist for several decades. Timescales of vegetation change were observed to vary between sites, but in general bare peat and acrocarpous mosses were likely to increase temporarily following burning, and a high abundance of graminoids a few years after fire was followed by dwarf shrub dominance in the longer term. These changes are likely to have consequences for peatland ecosystem services.