Interspecific Competition between Sphagnum Mosses on a Raised Bog

Sphagnum fuscum decreased initially in the hollows but recovered and showed a highly variable result after a decade, with an increase in area in many cases. It was not extinguished by the hollow species in any one case. These long-term results do not support the hypothesis that it is excluded from the hollows by competition, but the treatments did not include the wettest parts of the hollows. Among the hollow species S. balticum seemed to have a competitive advantage, but the trend was reversed in one year when S. tenellum regained area. This result stresses the importance of long-term experiments. There were also other instances when the conclusions drawn from the long-term monitoring differed from those reached after 4-5 years. The results suggest that these closely related species were on average rather similar in competitive ability in the hollows, but results varied considerably between nominal replicates. Competition also varied seasonally: S. balticum often lost area to S. fuscum and won area from S. tenellum in the autumn, with a compensation for these changes earlier in the summer. Variation in water level within habitat could not be shown to affect the outcome of competition between species.