Impacts of prescribed burning on Sphagnum mosses in a long-term peatland field experiment.

Understanding fire impacts on peatland vegetation can inform management to support function and prevent degradation of these important ecosystems. However, time since burn, interval between burns and number of past burns all have the potential to modify impacts. Grazing regime may also affect vegetation directly or via an interaction with burning. We used new, comprehensive survey data from a hillslope-scale field experiment initiated in 1954 to investigate the effects of burning and grazing treatments on Sphagnum. Historical data were consulted to aid interpretation of the results. The unburned reference and the most frequently burned (10-year rotation) treatments had greater Sphagnum abundance and hummock height than intermediate treatments (20-year rotation and no-burn since 1954). Abundance of the most common individual species (S. capillifolium, S. subnitens and S. papillosum) followed similar patterns. Light grazing had no impact on Sphagnum-related variables, nor did it interact with the burning treatments.These results suggest that in some cases fire has a negative impact on Sphagnum, and this can persist for several decades. However, fire return interval and other factors such as atmospheric pollution may alter effects, and in some cases Sphagnum abundance may recover. Fire severity and site specific conditions may also influence effects, so we advise consideration of these factors, and caution when using fire as a management tool on peatlands where Sphagnum is considered desirable.