Growth, production and interspecific competition in Sphagnum: effects of temperature, nitrogen and sulphur treatments on a boreal mire.

•  Growth and production of Sphagnum balticum and interspecific competition between S. balticum and either Sphagnum lindbergii or transplanted Sphagnum papillosum, were studied in a 4-yr field experiment in a poor fen. •  Temperature and influxes of nitrogen (N) and sulphur (S) were manipulated in a factorial design. The mean daily air temperature was increased by 3.6°C with glasshouse enclosures. Nitrogen loads were increased 15-fold and S loads seven-fold compared with the natural loads up to influxes observed during the 1980s in south-western Sweden. •  Production of S. balticum decreased with increasing temperature and N-influx. The N treatment significantly reduced the incremental length of S. balticum, and this reduction was reinforced with time (24% in the first year to 51% in the final year). The area covered by S. lindbergii changed with time in all treatments and S. papillosum area increased significantly in the temperature-treated plots. •  Growth, production and competitive patterns change if the environmental conditions change. Increased N deposition and raised temperature may transform mires currently dominated by Sphagnum into vascular-plant-dominated mires.